* Re: [PATCH v1 1/2] spi: qcom-geni: trace: Add trace events for Qualcomm GENI SPI
From: Mark Brown @ 2026-05-10 12:37 UTC (permalink / raw)
To: Praveen Talari
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers, linux-kernel,
linux-trace-kernel, linux-arm-msm, linux-spi,
MukeshKumarSavaliyamukesh.savaliya, AniketRandiveaniket.randive,
chandana.chiluveru, jyothi.seerapu
In-Reply-To: <4d90b061-95ab-40d4-83d2-13425e992d4d@oss.qualcomm.com>
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On Sat, May 09, 2026 at 07:37:26AM +0530, Praveen Talari wrote:
> Could you also please review the changes made in spi.c ?
> I would appreciate any feedback or suggestions you may have.
Please just sumbmit normal patches instead of sending partial patches in
reply to another thread unless something is really unclear.
> @@ -1658,6 +1658,11 @@ static int spi_transfer_one_message(struct
> spi_controller *ctlr,
>
> trace_spi_transfer_stop(msg, xfer);
>
> + if (spi_valid_txbuf(msg, xfer))
> + trace_spi_tx_data(msg->spi, xfer->tx_buf,
> xfer->len);
> + if (spi_valid_rxbuf(msg, xfer))
> + trace_spi_rx_data(msg->spi, xfer->rx_buf,
> xfer->len);
It feels like it'd be more helpful to log the transmit data before we do
the send.
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^ permalink raw reply
* Re: [PATCH RFC v5 10/53] KVM: guest_memfd: Add basic support for KVM_SET_MEMORY_ATTRIBUTES2
From: Liam R. Howlett @ 2026-05-10 13:43 UTC (permalink / raw)
To: Ackerley Tng
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
ira.weiny, jmattson, jthoughton, michael.roth, oupton,
pankaj.gupta, qperret, rick.p.edgecombe, rientjes, shivankg,
steven.price, tabba, willy, wyihan, yan.y.zhao, forkloop,
pratyush, suzuki.poulose, aneesh.kumar, Paolo Bonzini,
Sean Christopherson, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He, Barry Song,
Axel Rasmussen, Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng,
Shakeel Butt, Kiryl Shutsemau, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <CAEvNRgF9+Gr7UVEq-E2SQEb_XOQQMOXy9F_A2tA=DbNV_fJ0EQ@mail.gmail.com>
On 7 May 2026 12:56:11 GMT-04:00, Ackerley Tng <ackerleytng@google.com> wrote:
>"Liam R. Howlett" <liam@infradead.org> writes:
>
>> On 26/04/28 04:25PM, Ackerley Tng via B4 Relay wrote:
>>>
>>> [...snip...]
>>>
>>> +/*
>>> + * Preallocate memory for attributes to be stored on a maple tree, pointed to
>>> + * by mas. Adjacent ranges with attributes identical to the new attributes
>>> + * will be merged. Also sets mas's bounds up for storing attributes.
>>> + *
>>> + * This maintains the invariant that ranges with the same attributes will
>>> + * always be merged.
>>> + */
>>> +static int kvm_gmem_mas_preallocate(struct ma_state *mas, u64 attributes,
>>> + pgoff_t start, size_t nr_pages)
>>> +{
>>> + pgoff_t end = start + nr_pages;
>>> + pgoff_t last = end - 1;
>>> + void *entry;
>>> +
>>> + /* Try extending range. entry is NULL on overflow/wrap-around. */
>>> + mas_set_range(mas, end, end);
>>> + entry = mas_find(mas, end);
>
>Thank you for your reviews!
>
>>
>> Please read the documentation as I believe you have a bug here. What
>> happens if there is another range stored higher than end + 1?
>>
>
>The invariant in this maple tree is that contiguous ranges with the same
>attribute are stored as a single range.
>
>The goal of this first part is to get the entry at the index just after
>the requested range, and see what the attribute there is. If that
>attribute is what we're about to set, extend the requested range for
>storing to the end of that range.
>
>If there is another range higher than end + 1, with the invariant
>maintained, that attribute has to be different than the attribute stored
>at end. Hence, we only want to extend this requested range up till end.
>
mas_find() will look for an entry at the given address for the first search, and if it is not found it will continue to search upwards. Since you limit the search to end, it will work as you want and there isn't a bug as I was thinking in my sleep deprived state.
Since you are searching for exactly one address (end), it might serve you better to walk there. Maybe walking is a better API for what you are doing here?
>> Do you have testing of these functions somewhere?
>>
>
>GMEM_CONVERSION_MULTIPAGE_TEST_INIT_SHARED(indexing, 4) tests setting
>attributes in ranges. If test_page is 2,
>
>1. [0, 4) starts off shared (4 is the number of pages in the guest_memfd)
>2. [2, 3) is converted to private
> => so the ranges should now be [0, 2), [2, 3), [3, 4)
>3. [2, 3) is converted back to shared
> => so the ranges should now be [0, 4)
>
>I verified this by inserting some trace_printk()s and inspecting manually.
>
Thanks. I find the exclusive ranges a bit odd to think about in the maple tree context, but this test case makes sense. This is especially odd to look at a single index entry, at least for me.
I generally have a set of test cases and append any bug reproduces to that list so they are unlikely to reoccur. My testing is certainly different from what you'll be doing, but this method has done well with the quality of code improving over time, and limited (if any) regressions.
I actually insist that any fix has a test before I accept them. There are two reasons for this: 1. Avoiding the regression. 2. People really understand the bug if they can create a reproducer.
I hope this helps.
>>> + if (entry && xa_to_value(entry) == attributes)
>>> + last = mas->last;
>>> +
>>> + if (start > 0) {
>>> + mas_set_range(mas, start - 1, start - 1);
>>> + entry = mas_find(mas, start - 1);
>>> + if (entry && xa_to_value(entry) == attributes)
>>> + start = mas->index;
>>> + }
>>> +
>>> + mas_set_range(mas, start, last);
>>> + return mas_preallocate(mas, xa_mk_value(attributes), GFP_KERNEL);
>>> +}
>>> +
>>>
>>> [...snip...]
>>>
^ permalink raw reply
* Re: [PATCH 01/13] verification/rvgen: Switch LTL parser to Lark
From: Nam Cao @ 2026-05-10 18:18 UTC (permalink / raw)
To: Gabriele Monaco
Cc: Steven Rostedt, Wander Lairson Costa, linux-trace-kernel,
linux-kernel
In-Reply-To: <41f74dec0fab9d49a9b77ec994b102ba73fe060d.camel@redhat.com>
Gabriele Monaco <gmonaco@redhat.com> writes:
> It looks very neat! I didn't go through it fully just yet, though.
> This one works fine but there's a nit: the ASTNode's id starts from 1, but
> apparently the new grammar consider RULE as a node too, this results in
> variables in the generated header file starting from val2 (rather than val1).
>
> Unless I missed something here, we should probably start from 0:
Yep, thanks!
> Also it doesn't gracefully handle an invalid syntax, but that's probably still a
> work in progress.
We could catch Lark's exception. I will look into it.
Nam
^ permalink raw reply
* Re: [PATCH 03/13] verification/rvgen: Implement state and transition parser based on Lark
From: Nam Cao @ 2026-05-10 18:21 UTC (permalink / raw)
To: Gabriele Monaco
Cc: Steven Rostedt, Wander Lairson Costa, linux-trace-kernel,
linux-kernel
In-Reply-To: <dba16e4fe794c5aa237f3360fef5fc22ae32c60b.camel@redhat.com>
Gabriele Monaco <gmonaco@redhat.com> writes:
> Looks good, although I need to put more effort to understand the grammar.
> There's an issue parsing events though:
>
>> +class EventLabelParser:
>> + grammar = r'''
>> + events: event ("\\n" event)*
>> +
>> + event: name (";" guard)*
>> +
>> + guard: reset
>> + | rule
>> + | rule reset
>> + | reset rule
>
> I'm not sure if it could be solved better changing the grammar, but this doesn't
> work in case we have both a reset and a rule, e.g.:
>
> "event2;env1 == 0;reset(clk)"
>
> It apparently saves only one of them, the other would end up in args[2].
Thanks for pointing that out. The grammar is broken, it allows any
number of guards and does not require a ";" between reset and rule.
This grammar change fixes it:
diff --git a/tools/verification/rvgen/rvgen/automata.py b/tools/verification/rvgen/rvgen/automata.py
index cc42b8127fc0..d8c5e9028364 100644
--- a/tools/verification/rvgen/rvgen/automata.py
+++ b/tools/verification/rvgen/rvgen/automata.py
@@ -275,12 +275,12 @@ class EventLabelParser:
grammar = r'''
events: event ("\\n" event)*
- event: name (";" guard)*
+ event: name (";" guard)?
guard: reset
| rule
- | rule reset
- | reset rule
+ | rule ";" reset
+ | reset ";" rule
name: CNAME
@@ -312,6 +312,7 @@ class EventLabelParser:
return ConstraintCondition(*args)
def event(self, args):
+ assert(len(args) <= 2)
name = args[0]
rule, reset = None, None
if len(args) == 2:
^ permalink raw reply related
* Re: [PATCH bpf 1/2] uprobes/x86: Fix red zone clobbering in nop5 optimization
From: Jiri Olsa @ 2026-05-10 21:25 UTC (permalink / raw)
To: Andrii Nakryiko; +Cc: bpf, linux-trace-kernel, oleg, peterz, mingo, mhiramat
In-Reply-To: <20260509003146.976844-1-andrii@kernel.org>
On Fri, May 08, 2026 at 05:30:56PM -0700, Andrii Nakryiko wrote:
> The x86 uprobe nop5 optimization currently replaces a 5-byte NOP at the
> probe site with a CALL into a uprobe trampoline. CALL pushes a return
> address to [rsp-8]. On x86-64 this is inside the 128-byte red zone, where
> user code may keep temporary data without adjusting rsp.
>
> Use a 5-byte JMP instead. JMP does not write to the user stack, but it
> also does not provide a return address. Replace the single trampoline
> entry with a page of 16-byte slots. Each optimized probe jumps to its
> assigned slot, the slot moves rsp below the red zone, saves the registers
> clobbered by syscall, and invokes the uprobe syscall:
>
> Probe site: jmp slot_N (5B, replaces nop5)
>
> Slot N: lea -128(%rsp), %rsp (5B) skip red zone
> push %rcx (1B) save (syscall clobbers)
> push %r11 (2B) save (syscall clobbers)
> push %rax (1B) save (syscall uses for nr)
> mov $336, %eax (5B) uprobe syscall number
> syscall (2B)
>
> All slots contain identical code at different offsets, so the trampoline
> page is generated once at boot and mapped read-execute into each process.
> The syscall handler identifies the slot from regs->ip, which points just
> after the syscall instruction, and uses a per-mm slot table to recover the
> original probe address.
>
> The uprobe syscall does not return to the trampoline slot. The handler
> restores the probe-site register state, runs the uprobe consumers, sets
> pt_regs to continue at probe_addr + 5 unless a consumer redirected
> execution, and returns directly through the IRET path. This preserves
> general purpose registers, including rcx and r11, without requiring any
> post-syscall cleanup code in the trampoline and avoids call/ret, RSB, and
> shadow stack concerns.
>
> Protect the per-mm trampoline list with RCU and free trampoline metadata
> with kfree_rcu(). This lets the syscall path resolve trampoline slots
> without taking mmap_lock. The optimized-instruction detection path also
> walks the trampoline list under an RCU read-side lock. Since that path
> starts from the JMP target, it translates the slot start to the post-syscall
> IP expected by the shared resolver before checking the trampoline mapping.
>
> Each trampoline page provides 256 slots. Slots stay permanently assigned
> to their first probe address and are reused only when the same address is
> probed again. Reassigning detached slots is deliberately avoided because a
> thread can remain in a trampoline for an unbounded time due to ptrace,
> interrupts, or scheduling delays. If a reachable trampoline page runs out
> of slots, probes that cannot allocate a slot fall back to the slower INT3
> path.
>
> Require the entire trampoline page to be reachable by a rel32 JMP before
> reusing it for a probe. This keeps every slot in the page within the range
> that can be encoded at the probe site.
>
> Change the error code returned when the uprobe syscall is invoked outside
> a kernel-generated trampoline from -ENXIO to -EPROTO. This lets libbpf and
> similar libraries distinguish fixed kernels from kernels with the
> red-zone-clobbering implementation and enable nop5 optimization only on
> fixed kernels.
>
> Performance (usdt single-thread, M/s):
>
> usdt-nop usdt-nop5-base usdt-nop5-fix nop5-change iret%
> Skylake 3.149 6.422 4.865 -24.3% 39.1%
> Milan 2.910 3.443 3.820 +11.0% 24.3%
> Sapphire Rapids 1.896 4.023 3.693 -8.2% 24.9%
> Bergamo 3.393 3.895 3.849 -1.2% 24.5%
>
> The fixed nop5 path remains faster than the non-optimized INT3 path on all
> measured systems. The regression relative to the old CALL-based trampoline
> comes from IRET being more expensive than SYSRET, most noticeably on older
> Intel Skylake. Newer Intel CPUs and tested AMD CPUs have lower IRET cost,
> and AMD Milan improves because removing mmap_lock from the hot path more
> than offsets the IRET cost.
>
> Multi-threaded throughput scales nearly linearly with the number of CPUs, like
> it used to, thanks to lockless RCU-protected uprobe trampoline lookup.
hi,
thanks a lot for the fix
FWIW we discussed also an option to have 10-bytes nop and do:
[rsp+0x80, call trampoline]
we would not need the slots re-use logic, but not sure what other
surprises there are with 10-bytes nop
I tried that change [1], it seems to work, but it has other
difficulties, like I think the unoptimized path needs to do:
[rsp+0x80, call trampoline] -> [jmp end of 10-bytes nop]
instead of patching back the 10-byte nop, because some thread
could be inside the nop area already.
jirka
[1] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?h=redzone_fix&id=74b09240289dba8368c2783b771e678b2cc31574
>
> Fixes: ba2bfc97b462 ("uprobes/x86: Add support to optimize uprobes")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
> arch/x86/include/asm/uprobes.h | 18 ++
> arch/x86/kernel/uprobes.c | 262 ++++++++++--------
> tools/lib/bpf/features.c | 8 +-
> .../selftests/bpf/prog_tests/uprobe_syscall.c | 5 +-
> tools/testing/selftests/bpf/prog_tests/usdt.c | 2 +-
> 5 files changed, 181 insertions(+), 114 deletions(-)
>
> diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
> index 362210c79998..a7cf5c92d95a 100644
> --- a/arch/x86/include/asm/uprobes.h
> +++ b/arch/x86/include/asm/uprobes.h
> @@ -25,6 +25,24 @@ enum {
> ARCH_UPROBE_FLAG_OPTIMIZE_FAIL = 1,
> };
>
> +/*
> + * Trampoline page layout: identical 16-byte slots, each containing:
> + * lea -128(%rsp), %rsp (5B) skip red zone
> + * push %rcx (1B) save (syscall clobbers)
> + * push %r11 (2B) save (syscall clobbers)
> + * push %rax (1B) save (syscall uses for nr)
> + * mov $336, %eax (5B) uprobe syscall number
> + * syscall (2B)
> + * = 16B, no padding needed
> + *
> + * The handler identifies which probe fired from regs->ip (each
> + * slot is at a unique offset), looks up the probe address from a
> + * per-process table, and returns directly to probe_addr+5 via iret
> + * with all registers restored.
> + */
> +#define UPROBE_TRAMP_SLOT_SIZE 16
> +#define UPROBE_TRAMP_MAX_SLOTS (PAGE_SIZE / UPROBE_TRAMP_SLOT_SIZE)
> +
> struct uprobe_xol_ops;
>
> struct arch_uprobe {
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index ebb1baf1eb1d..7e1f14200bbb 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -633,16 +633,25 @@ static struct vm_special_mapping tramp_mapping = {
>
> struct uprobe_trampoline {
> struct hlist_node node;
> + struct rcu_head rcu;
> unsigned long vaddr;
> + unsigned long probe_addrs[UPROBE_TRAMP_MAX_SLOTS];
> };
>
> -static bool is_reachable_by_call(unsigned long vtramp, unsigned long vaddr)
> +
> +static bool is_reachable_by_jmp(unsigned long dst, unsigned long src)
> {
> - long delta = (long)(vaddr + 5 - vtramp);
> + long delta = (long)(dst - (src + JMP32_INSN_SIZE));
>
> return delta >= INT_MIN && delta <= INT_MAX;
> }
>
> +static bool is_reachable_by_trampoline(unsigned long vtramp, unsigned long vaddr)
> +{
> + return is_reachable_by_jmp(vtramp, vaddr) &&
> + is_reachable_by_jmp(vtramp + PAGE_SIZE - 1, vaddr);
> +}
> +
> static unsigned long find_nearest_trampoline(unsigned long vaddr)
> {
> struct vm_unmapped_area_info info = {
> @@ -711,6 +720,21 @@ static struct uprobe_trampoline *create_uprobe_trampoline(unsigned long vaddr)
> return tramp;
> }
>
> +static int tramp_alloc_slot(struct uprobe_trampoline *tramp, unsigned long probe_addr)
> +{
> + int i;
> +
> + for (i = 0; i < UPROBE_TRAMP_MAX_SLOTS; i++) {
> + if (tramp->probe_addrs[i] == probe_addr)
> + return i;
> + if (tramp->probe_addrs[i] == 0) {
> + tramp->probe_addrs[i] = probe_addr;
> + return i;
> + }
> + }
> + return -ENOSPC;
> +}
> +
> static struct uprobe_trampoline *get_uprobe_trampoline(unsigned long vaddr, bool *new)
> {
> struct uprobes_state *state = ¤t->mm->uprobes_state;
> @@ -720,7 +744,7 @@ static struct uprobe_trampoline *get_uprobe_trampoline(unsigned long vaddr, bool
> return NULL;
>
> hlist_for_each_entry(tramp, &state->head_tramps, node) {
> - if (is_reachable_by_call(tramp->vaddr, vaddr)) {
> + if (is_reachable_by_trampoline(tramp->vaddr, vaddr)) {
> *new = false;
> return tramp;
> }
> @@ -731,7 +755,7 @@ static struct uprobe_trampoline *get_uprobe_trampoline(unsigned long vaddr, bool
> return NULL;
>
> *new = true;
> - hlist_add_head(&tramp->node, &state->head_tramps);
> + hlist_add_head_rcu(&tramp->node, &state->head_tramps);
> return tramp;
> }
>
> @@ -742,8 +766,8 @@ static void destroy_uprobe_trampoline(struct uprobe_trampoline *tramp)
> * because there's no easy way to make sure none of the threads
> * is still inside the trampoline.
> */
> - hlist_del(&tramp->node);
> - kfree(tramp);
> + hlist_del_rcu(&tramp->node);
> + kfree_rcu(tramp, rcu);
> }
>
> void arch_uprobe_init_state(struct mm_struct *mm)
> @@ -761,147 +785,153 @@ void arch_uprobe_clear_state(struct mm_struct *mm)
> destroy_uprobe_trampoline(tramp);
> }
>
> -static bool __in_uprobe_trampoline(unsigned long ip)
> +/*
> + * Find the trampoline containing @ip. If @probe_addr is non-NULL, also
> + * resolve the slot index from @ip and return the probe address.
> + *
> + * @ip is expected to point right after the syscall instruction, i.e.,
> + * at the end of the slot (slot_start + UPROBE_TRAMP_SLOT_SIZE).
> + */
> +static bool resolve_uprobe_addr(unsigned long ip, unsigned long *probe_addr)
> {
> - struct vm_area_struct *vma = vma_lookup(current->mm, ip);
> + struct uprobes_state *state = ¤t->mm->uprobes_state;
> + struct uprobe_trampoline *tramp;
>
> - return vma && vma_is_special_mapping(vma, &tramp_mapping);
> -}
> + hlist_for_each_entry_rcu(tramp, &state->head_tramps, node) {
> + /*
> + * ip points to after syscall, so it's on 16 byte boundary,
> + * which means that valid ip can point right after the page
> + * and should never be at zero offset within the page
> + */
> + if (ip <= tramp->vaddr || ip > tramp->vaddr + PAGE_SIZE)
> + continue;
>
> -static bool in_uprobe_trampoline(unsigned long ip)
> -{
> - struct mm_struct *mm = current->mm;
> - bool found, retry = true;
> - unsigned int seq;
> + if (probe_addr) {
> + /* we already validated ip is within expected range */
> + unsigned int slot = (ip - tramp->vaddr - 1) / UPROBE_TRAMP_SLOT_SIZE;
> + unsigned long addr = tramp->probe_addrs[slot];
>
> - rcu_read_lock();
> - if (mmap_lock_speculate_try_begin(mm, &seq)) {
> - found = __in_uprobe_trampoline(ip);
> - retry = mmap_lock_speculate_retry(mm, seq);
> - }
> - rcu_read_unlock();
> + *probe_addr = addr;
> + if (addr == 0)
> + return false;
> + }
>
> - if (retry) {
> - mmap_read_lock(mm);
> - found = __in_uprobe_trampoline(ip);
> - mmap_read_unlock(mm);
> + return true;
> }
> - return found;
> + return false;
> +}
> +
> +static bool in_uprobe_trampoline(unsigned long ip, unsigned long *probe_addr)
> +{
> + guard(rcu)();
> + return resolve_uprobe_addr(ip, probe_addr);
> }
>
> /*
> - * See uprobe syscall trampoline; the call to the trampoline will push
> - * the return address on the stack, the trampoline itself then pushes
> - * cx, r11 and ax.
> + * The trampoline slot pushes cx, r11, ax (the registers syscall clobbers)
> + * before doing the uprobe syscall. No return address is pushed — the
> + * probe site uses jmp, not call.
> */
> struct uprobe_syscall_args {
> unsigned long ax;
> unsigned long r11;
> unsigned long cx;
> - unsigned long retaddr;
> };
>
> +#define UPROBE_TRAMP_REDZONE 128
> +
> SYSCALL_DEFINE0(uprobe)
> {
> struct pt_regs *regs = task_pt_regs(current);
> struct uprobe_syscall_args args;
> - unsigned long ip, sp, sret;
> + unsigned long probe_addr;
> int err;
>
> /* Allow execution only from uprobe trampolines. */
> - if (!in_uprobe_trampoline(regs->ip))
> - return -ENXIO;
> + if (!in_uprobe_trampoline(regs->ip, &probe_addr))
> + return -EPROTO;
>
> err = copy_from_user(&args, (void __user *)regs->sp, sizeof(args));
> if (err)
> goto sigill;
>
> - ip = regs->ip;
> -
> /*
> - * expose the "right" values of ax/r11/cx/ip/sp to uprobe_consumer/s, plus:
> - * - adjust ip to the probe address, call saved next instruction address
> - * - adjust sp to the probe's stack frame (check trampoline code)
> + * Restore the register state as it was at the probe site:
> + * - ax/r11/cx from the trampoline-saved copies on user stack
> + * - adjust ip to the probe address based on matching slot
> + * - adjust sp to skip red zone and pushed args
> */
> regs->ax = args.ax;
> regs->r11 = args.r11;
> regs->cx = args.cx;
> - regs->ip = args.retaddr - 5;
> - regs->sp += sizeof(args);
> + regs->ip = probe_addr;
> + regs->sp += sizeof(args) + UPROBE_TRAMP_REDZONE;
> regs->orig_ax = -1;
>
> - sp = regs->sp;
> -
> - err = shstk_pop((u64 *)&sret);
> - if (err == -EFAULT || (!err && sret != args.retaddr))
> - goto sigill;
> -
> - handle_syscall_uprobe(regs, regs->ip);
> + handle_syscall_uprobe(regs, probe_addr);
>
> /*
> - * Some of the uprobe consumers has changed sp, we can do nothing,
> - * just return via iret.
> + * Skip the jmp instruction at the probe site (5 bytes) unless
> + * a consumer redirected execution elsewhere.
> */
> - if (regs->sp != sp) {
> - /* skip the trampoline call */
> - if (args.retaddr - 5 == regs->ip)
> - regs->ip += 5;
> - return regs->ax;
> - }
> + if (regs->ip == probe_addr)
> + regs->ip = probe_addr + 5;
>
> - regs->sp -= sizeof(args);
> -
> - /* for the case uprobe_consumer has changed ax/r11/cx */
> - args.ax = regs->ax;
> - args.r11 = regs->r11;
> - args.cx = regs->cx;
> -
> - /* keep return address unless we are instructed otherwise */
> - if (args.retaddr - 5 != regs->ip)
> - args.retaddr = regs->ip;
> -
> - if (shstk_push(args.retaddr) == -EFAULT)
> - goto sigill;
> -
> - regs->ip = ip;
> -
> - err = copy_to_user((void __user *)regs->sp, &args, sizeof(args));
> - if (err)
> - goto sigill;
> -
> - /* ensure sysret, see do_syscall_64() */
> - regs->r11 = regs->flags;
> - regs->cx = regs->ip;
> - return 0;
> + /*
> + * Return via iret by returning regs->ax. This preserves all
> + * GP registers (including cx and r11) without needing any
> + * user-space cleanup code. The iret path is used because we
> + * don't set up cx/r11 for sysret.
> + */
> + return regs->ax;
>
> sigill:
> force_sig(SIGILL);
> return -1;
> }
>
> +/*
> + * All uprobe trampoline slots are identical: skip the red zone,
> + * save the three registers that syscall clobbers, then invoke
> + * the uprobe syscall. The handler returns directly to the probe
> + * caller via iret. Execution never returns to the trampoline.
> + */
> asm (
> ".pushsection .rodata\n"
> - ".balign " __stringify(PAGE_SIZE) "\n"
> - "uprobe_trampoline_entry:\n"
> + ".balign " __stringify(UPROBE_TRAMP_SLOT_SIZE) "\n"
> + "uprobe_trampoline_slot:\n"
> + "lea -128(%rsp), %rsp\n"
> "push %rcx\n"
> "push %r11\n"
> "push %rax\n"
> - "mov $" __stringify(__NR_uprobe) ", %rax\n"
> + "mov $" __stringify(__NR_uprobe) ", %eax\n"
> "syscall\n"
> - "pop %rax\n"
> - "pop %r11\n"
> - "pop %rcx\n"
> - "ret\n"
> - "int3\n"
> - ".balign " __stringify(PAGE_SIZE) "\n"
> + "uprobe_trampoline_slot_end:\n"
> ".popsection\n"
> );
>
> -extern u8 uprobe_trampoline_entry[];
> +extern u8 uprobe_trampoline_slot[];
> +extern u8 uprobe_trampoline_slot_end[];
>
> static int __init arch_uprobes_init(void)
> {
> - tramp_mapping_pages[0] = virt_to_page(uprobe_trampoline_entry);
> + unsigned int slot_size = uprobe_trampoline_slot_end - uprobe_trampoline_slot;
> + struct page *page;
> + u8 *page_addr;
> + int i;
> +
> + BUILD_BUG_ON(UPROBE_TRAMP_SLOT_SIZE != 16);
> + WARN_ON_ONCE(slot_size != UPROBE_TRAMP_SLOT_SIZE);
> +
> + page = alloc_page(GFP_KERNEL);
> + if (!page)
> + return -ENOMEM;
> +
> + page_addr = page_address(page);
> + for (i = 0; i < UPROBE_TRAMP_MAX_SLOTS; i++)
> + memcpy(page_addr + i * UPROBE_TRAMP_SLOT_SIZE, uprobe_trampoline_slot, slot_size);
> +
> + tramp_mapping_pages[0] = page;
> return 0;
> }
>
> @@ -909,7 +939,7 @@ late_initcall(arch_uprobes_init);
>
> enum {
> EXPECT_SWBP,
> - EXPECT_CALL,
> + EXPECT_JMP,
> };
>
> struct write_opcode_ctx {
> @@ -917,14 +947,14 @@ struct write_opcode_ctx {
> int expect;
> };
>
> -static int is_call_insn(uprobe_opcode_t *insn)
> +static int is_jmp_insn(uprobe_opcode_t *insn)
> {
> - return *insn == CALL_INSN_OPCODE;
> + return *insn == JMP32_INSN_OPCODE;
> }
>
> /*
> * Verification callback used by int3_update uprobe_write calls to make sure
> - * the underlying instruction is as expected - either int3 or call.
> + * the underlying instruction is as expected - either int3 or jmp.
> */
> static int verify_insn(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode,
> int nbytes, void *data)
> @@ -939,8 +969,8 @@ static int verify_insn(struct page *page, unsigned long vaddr, uprobe_opcode_t *
> if (is_swbp_insn(&old_opcode[0]))
> return 1;
> break;
> - case EXPECT_CALL:
> - if (is_call_insn(&old_opcode[0]))
> + case EXPECT_JMP:
> + if (is_jmp_insn(&old_opcode[0]))
> return 1;
> break;
> }
> @@ -978,7 +1008,7 @@ static int int3_update(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> * so we can skip this step for optimize == true.
> */
> if (!optimize) {
> - ctx.expect = EXPECT_CALL;
> + ctx.expect = EXPECT_JMP;
> err = uprobe_write(auprobe, vma, vaddr, &int3, 1, verify_insn,
> true /* is_register */, false /* do_update_ref_ctr */,
> &ctx);
> @@ -1015,13 +1045,13 @@ static int int3_update(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> }
>
> static int swbp_optimize(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> - unsigned long vaddr, unsigned long tramp)
> + unsigned long vaddr, unsigned long slot_vaddr)
> {
> - u8 call[5];
> + u8 jmp[5];
>
> - __text_gen_insn(call, CALL_INSN_OPCODE, (const void *) vaddr,
> - (const void *) tramp, CALL_INSN_SIZE);
> - return int3_update(auprobe, vma, vaddr, call, true /* optimize */);
> + __text_gen_insn(jmp, JMP32_INSN_OPCODE, (const void *) vaddr,
> + (const void *) slot_vaddr, JMP32_INSN_SIZE);
> + return int3_update(auprobe, vma, vaddr, jmp, true /* optimize */);
> }
>
> static int swbp_unoptimize(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> @@ -1049,11 +1079,17 @@ static bool __is_optimized(uprobe_opcode_t *insn, unsigned long vaddr)
> struct __packed __arch_relative_insn {
> u8 op;
> s32 raddr;
> - } *call = (struct __arch_relative_insn *) insn;
> + } *jmp = (struct __arch_relative_insn *) insn;
>
> - if (!is_call_insn(insn))
> + if (!is_jmp_insn(&jmp->op))
> return false;
> - return __in_uprobe_trampoline(vaddr + 5 + call->raddr);
> +
> + guard(rcu)();
> + /*
> + * resolve_uprobe_addr() expects IP pointing after syscall instruction
> + * (after the slot, basically), so adjust jump target address accordingly
> + */
> + return resolve_uprobe_addr(vaddr + 5 + jmp->raddr + UPROBE_TRAMP_SLOT_SIZE, NULL);
> }
>
> static int is_optimized(struct mm_struct *mm, unsigned long vaddr)
> @@ -1113,8 +1149,9 @@ static int __arch_uprobe_optimize(struct arch_uprobe *auprobe, struct mm_struct
> {
> struct uprobe_trampoline *tramp;
> struct vm_area_struct *vma;
> + unsigned long slot_vaddr;
> bool new = false;
> - int err = 0;
> + int slot, err;
>
> vma = find_vma(mm, vaddr);
> if (!vma)
> @@ -1122,8 +1159,17 @@ static int __arch_uprobe_optimize(struct arch_uprobe *auprobe, struct mm_struct
> tramp = get_uprobe_trampoline(vaddr, &new);
> if (!tramp)
> return -EINVAL;
> - err = swbp_optimize(auprobe, vma, vaddr, tramp->vaddr);
> - if (WARN_ON_ONCE(err) && new)
> +
> + slot = tramp_alloc_slot(tramp, vaddr);
> + if (slot < 0) {
> + if (new)
> + destroy_uprobe_trampoline(tramp);
> + return slot;
> + }
> +
> + slot_vaddr = tramp->vaddr + slot * UPROBE_TRAMP_SLOT_SIZE;
> + err = swbp_optimize(auprobe, vma, vaddr, slot_vaddr);
> + if (err && new)
> destroy_uprobe_trampoline(tramp);
> return err;
> }
> diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
> index 4f19a0d79b0c..1b6c113357b2 100644
> --- a/tools/lib/bpf/features.c
> +++ b/tools/lib/bpf/features.c
> @@ -577,10 +577,12 @@ static int probe_ldimm64_full_range_off(int token_fd)
> static int probe_uprobe_syscall(int token_fd)
> {
> /*
> - * If kernel supports uprobe() syscall, it will return -ENXIO when called
> - * from the outside of a kernel-generated uprobe trampoline.
> + * If kernel supports uprobe() syscall, it will return -EPROTO when
> + * called from outside a kernel-generated uprobe trampoline.
> + * Older kernels with the red-zone-clobbering bug return -ENXIO;
> + * we only enable the nop5 optimization on fixed kernels.
> */
> - return syscall(__NR_uprobe) < 0 && errno == ENXIO;
> + return syscall(__NR_uprobe) < 0 && errno == EPROTO;
> }
> #else
> static int probe_uprobe_syscall(int token_fd)
> diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> index 955a37751b52..0d5eb4cd1ddf 100644
> --- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> @@ -422,7 +422,8 @@ static void *check_attach(struct uprobe_syscall_executed *skel, trigger_t trigge
> /* .. and check the trampoline is as expected. */
> call = (struct __arch_relative_insn *) addr;
> tramp = (void *) (call + 1) + call->raddr;
> - ASSERT_EQ(call->op, 0xe8, "call");
> + tramp = (void *)((unsigned long)tramp & ~(getpagesize() - 1UL));
> + ASSERT_EQ(call->op, 0xe9, "jmp");
> ASSERT_OK(find_uprobes_trampoline(tramp), "uprobes_trampoline");
>
> return tramp;
> @@ -762,7 +763,7 @@ static void test_uprobe_error(void)
> long err = syscall(__NR_uprobe);
>
> ASSERT_EQ(err, -1, "error");
> - ASSERT_EQ(errno, ENXIO, "errno");
> + ASSERT_EQ(errno, EPROTO, "errno");
> }
>
> static void __test_uprobe_syscall(void)
> diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
> index 69759b27794d..9d3744d4e936 100644
> --- a/tools/testing/selftests/bpf/prog_tests/usdt.c
> +++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
> @@ -329,7 +329,7 @@ static void subtest_optimized_attach(void)
> ASSERT_EQ(*addr_2, 0x90, "nop");
>
> /* call is on addr_2 + 1 address */
> - ASSERT_EQ(*(addr_2 + 1), 0xe8, "call");
> + ASSERT_EQ(*(addr_2 + 1), 0xe9, "jmp");
> ASSERT_EQ(skel->bss->executed, 4, "executed");
>
> cleanup:
> --
> 2.53.0-Meta
>
^ permalink raw reply
* [PATCH] uprobes: Use flexible array for xol_area bitmap
From: Rosen Penev @ 2026-05-10 21:41 UTC (permalink / raw)
To: linux-trace-kernel
Cc: Masami Hiramatsu, Oleg Nesterov, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Mark Rutland,
Alexander Shishkin, Jiri Olsa, Ian Rogers, Adrian Hunter,
James Clark, open list:UPROBES,
open list:PERFORMANCE EVENTS SUBSYSTEM
The XOL slot bitmap has the same lifetime as struct xol_area, but it
is currently allocated separately. That adds another allocation
failure path and a matching cleanup branch without buying any extra
flexibility.
Store the bitmap as a flexible array member and allocate it together
with the xol_area using kzalloc_flex(). The bitmap remains
zero-initialized, while the allocation and error handling become
simpler.
Assisted-by: Codex:GPT-5.5
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
kernel/events/uprobes.c | 13 +++----------
1 file changed, 3 insertions(+), 10 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 4084e926e284..9ef74c2ad390 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -108,7 +108,6 @@ static LIST_HEAD(delayed_uprobe_list);
*/
struct xol_area {
wait_queue_head_t wq; /* if all slots are busy */
- unsigned long *bitmap; /* 0 = free slot */
struct page *page;
/*
@@ -117,6 +116,7 @@ struct xol_area {
* the vma go away, and we must handle that reasonably gracefully.
*/
unsigned long vaddr; /* Page(s) of instruction slots */
+ unsigned long bitmap[]; /* 0 = free slot */
};
static void uprobe_warn(struct task_struct *t, const char *msg)
@@ -1755,18 +1755,13 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
struct xol_area *area;
void *insns;
- area = kzalloc_obj(*area);
+ area = kzalloc_flex(*area, bitmap, BITS_TO_LONGS(UINSNS_PER_PAGE));
if (unlikely(!area))
goto out;
- area->bitmap = kcalloc(BITS_TO_LONGS(UINSNS_PER_PAGE), sizeof(long),
- GFP_KERNEL);
- if (!area->bitmap)
- goto free_area;
-
area->page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
if (!area->page)
- goto free_bitmap;
+ goto free_area;
area->vaddr = vaddr;
init_waitqueue_head(&area->wq);
@@ -1779,8 +1774,6 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
return area;
__free_page(area->page);
- free_bitmap:
- kfree(area->bitmap);
free_area:
kfree(area);
out:
--
2.54.0
^ permalink raw reply related
* Re: [PATCH v1 1/2] spi: qcom-geni: trace: Add trace events for Qualcomm GENI SPI
From: Praveen Talari @ 2026-05-11 2:50 UTC (permalink / raw)
To: Mark Brown
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers, linux-kernel,
linux-trace-kernel, linux-arm-msm, linux-spi,
MukeshKumarSavaliyamukesh.savaliya, AniketRandiveaniket.randive,
chandana.chiluveru, jyothi.seerapu
In-Reply-To: <agB8AgF3qVqDw60Z@sirena.co.uk>
HI Mark,
On 10-05-2026 18:07, Mark Brown wrote:
> On Sat, May 09, 2026 at 07:37:26AM +0530, Praveen Talari wrote:
>
>> Could you also please review the changes made in spi.c ?
>> I would appreciate any feedback or suggestions you may have.
> Please just sumbmit normal patches instead of sending partial patches in
> reply to another thread unless something is really unclear.
Sure, I will send the patches next. I just wanted to confirm a few points
>
>> @@ -1658,6 +1658,11 @@ static int spi_transfer_one_message(struct
>> spi_controller *ctlr,
>>
>> trace_spi_transfer_stop(msg, xfer);
>>
>> + if (spi_valid_txbuf(msg, xfer))
>> + trace_spi_tx_data(msg->spi, xfer->tx_buf,
>> xfer->len);
>> + if (spi_valid_rxbuf(msg, xfer))
>> + trace_spi_rx_data(msg->spi, xfer->rx_buf,
>> xfer->len);
> It feels like it'd be more helpful to log the transmit data before we do
> the send.
Sure. will take care in next patch-set.
Thanks,
Praveen Talari
^ permalink raw reply
* Re: [PATCH] uprobes: Use flexible array for xol_area bitmap
From: Masami Hiramatsu @ 2026-05-11 4:33 UTC (permalink / raw)
To: Rosen Penev
Cc: linux-trace-kernel, Masami Hiramatsu, Oleg Nesterov,
Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Namhyung Kim, Mark Rutland, Alexander Shishkin, Jiri Olsa,
Ian Rogers, Adrian Hunter, James Clark, open list:UPROBES,
open list:PERFORMANCE EVENTS SUBSYSTEM
In-Reply-To: <20260510214118.41926-1-rosenp@gmail.com>
On Sun, 10 May 2026 14:41:18 -0700
Rosen Penev <rosenp@gmail.com> wrote:
> The XOL slot bitmap has the same lifetime as struct xol_area, but it
> is currently allocated separately. That adds another allocation
> failure path and a matching cleanup branch without buying any extra
> flexibility.
>
> Store the bitmap as a flexible array member and allocate it together
> with the xol_area using kzalloc_flex(). The bitmap remains
> zero-initialized, while the allocation and error handling become
> simpler.
>
You also have to update uprobe_clear_state(), because area->bitmap
is no longer allocated separately.
Thank you,
> Assisted-by: Codex:GPT-5.5
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
> kernel/events/uprobes.c | 13 +++----------
> 1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 4084e926e284..9ef74c2ad390 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -108,7 +108,6 @@ static LIST_HEAD(delayed_uprobe_list);
> */
> struct xol_area {
> wait_queue_head_t wq; /* if all slots are busy */
> - unsigned long *bitmap; /* 0 = free slot */
>
> struct page *page;
> /*
> @@ -117,6 +116,7 @@ struct xol_area {
> * the vma go away, and we must handle that reasonably gracefully.
> */
> unsigned long vaddr; /* Page(s) of instruction slots */
> + unsigned long bitmap[]; /* 0 = free slot */
> };
>
> static void uprobe_warn(struct task_struct *t, const char *msg)
> @@ -1755,18 +1755,13 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
> struct xol_area *area;
> void *insns;
>
> - area = kzalloc_obj(*area);
> + area = kzalloc_flex(*area, bitmap, BITS_TO_LONGS(UINSNS_PER_PAGE));
> if (unlikely(!area))
> goto out;
>
> - area->bitmap = kcalloc(BITS_TO_LONGS(UINSNS_PER_PAGE), sizeof(long),
> - GFP_KERNEL);
> - if (!area->bitmap)
> - goto free_area;
> -
> area->page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
> if (!area->page)
> - goto free_bitmap;
> + goto free_area;
>
> area->vaddr = vaddr;
> init_waitqueue_head(&area->wq);
> @@ -1779,8 +1774,6 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
> return area;
>
> __free_page(area->page);
> - free_bitmap:
> - kfree(area->bitmap);
> free_area:
> kfree(area);
> out:
> --
> 2.54.0
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply
* [RFC v7 0/7] ext4: fast commit: snapshot inode state for FC log
From: Li Chen @ 2026-05-11 8:42 UTC (permalink / raw)
To: Zhang Yi, Theodore Ts'o, Andreas Dilger
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers, linux-ext4,
linux-trace-kernel, linux-kernel
Hi,
(This RFC v7 series is rebased onto linux-next master as of 2026-05-09,
commit e98d21c170b0 ("Add linux-next specific files for 20260508").)
Zhang Yi in RFC v3 review pointed out that postponing lockdep assertions only
masks the issue, and that sleeping in ext4_fc_track_inode() while holding
i_data_sem can form a real ABBA deadlock if the fast commit writer also needs
i_data_sem while the inode is in FC_COMMITTING.
Zhang Yi suggested two possible directions to address the root cause:
1. "Ha, the solution seems to have already been listed in the TODOs in
fast_commit.c.
Change ext4_fc_commit() to lookup logical to physical mapping using extent
status tree. This would get rid of the need to call ext4_fc_track_inode()
before acquiring i_data_sem. To do that we would need to ensure that
modified extents from the extent status tree are not evicted from memory."
2. "Alternatively, recording the mapped range of tracking might also be
feasible."
This series implements a hybrid way: it implements approach 2 by snapshotting inode image
and mapped ranges at commit time, and consuming only snapshots during log
writing.
Approach 2 still needs a mapping source while building the snapshot
(logical-to-physical and unwritten/hole semantics). Calling ext4_map_blocks()
there would take i_data_sem and can block inside the
jbd2_journal_lock_updates() window, which risks deadlocks or unbounded stalls.
So the snapshot path uses approach 1's extent status lookups as a best-effort
mapping source to avoid ext4_map_blocks().
I did not fully implement approach 1 (making extent status lookups
authoritative by preventing reclaim of needed entries) because that would need
additional pinning/integration under memory pressure and a larger correctness
surface. Instead, the extent status tree is treated as a cache and the
snapshot path falls back to full commit on cache misses or unstable mappings
(e.g. delayed allocation).
Lock inversion / deadlock model (before):
CPU0 (metadata update) CPU1 (fast commit)
-------------------- -----------------
... hold i_data_sem (A) mutex_lock(s_fc_lock) (B)
ext4_fc_track_inode() ext4_fc_write_inode_data()
mutex_lock(s_fc_lock) (B) ext4_map_blocks()
wait FC_COMMITTING (sleep) down_read(i_data_sem) (A)
This creates i_data_sem (A) -> s_fc_lock (B) on update paths, and
s_fc_lock (B) -> i_data_sem (A) on commit paths. Once CPU0 sleeps while
holding (A), CPU1 can block on (A) while holding (B), completing the ABBA
cycle.
New model (this series):
CPU0 (metadata update) CPU1 (fast commit)
-------------------- -----------------
... maybe hold i_data_sem (A) jbd2_journal_lock_updates()
ext4_fc_track_*() snapshot inode + ranges (no map_blocks)
mutex_lock(s_fc_lock) (B) jbd2_journal_unlock_updates()
if FC_COMMITTING: set FC_REQUEUE s_fc_lock (B)
no sleep write FC log from snapshots only
cleanup: clear COMMITTING, requeue if set
The commit path no longer takes i_data_sem while holding s_fc_lock, and
tracking no longer sleeps waiting for FC_COMMITTING. If an inode is updated
during a fast commit, EXT4_STATE_FC_REQUEUE records that fact and the inode
is moved to FC_Q_STAGING for the next commit.
The only remaining FC_COMMITTING waiter is ext4_fc_del(), which drops
s_fc_lock before sleeping.
This series snapshots the on-disk inode and tracked data ranges while journal
updates are locked and existing handles are drained. The log writing phase then
serializes only snapshots, so it no longer needs to call ext4_map_blocks() and
take i_data_sem under s_fc_lock. This is done in two steps: patch 1 drops
ext4_map_blocks() from log writing by introducing commit-time snapshots, and
patch 5 drops ext4_map_blocks() from the snapshot path by using the extent
status cache. The snapshot also records whether a mapped extent is unwritten,
so the ADD_RANGE records (and replay) preserve unwritten semantics.
Snapshotting runs under jbd2_journal_lock_updates(). Since a cache miss in
ext4_get_inode_loc() can start synchronous inode table I/O and stall handle
starts for milliseconds, patch 1 uses ext4_get_inode_loc_noio() and falls back
to full commit if the inode table block is not present or not uptodate.
ext4_fc_track_inode() also stops waiting for FC_COMMITTING. Updates during an
ongoing fast commit are marked with EXT4_STATE_FC_REQUEUE and are replayed in
the next fast commit, while ext4_fc_del() waits for FC_COMMITTING so an inode
cannot be removed while the commit thread is still using it.
The extent status tree is a cache, not an authoritative source, so the snapshot
path falls back to full commit on cache misses or unstable mappings (e.g.
delayed allocation). This includes cases where extent status entries are not
present (or have been reclaimed) under memory pressure. The snapshot path does
not try to rebuild mappings by calling ext4_map_blocks(); instead it simply
marks the transaction fast commit ineligible.
To keep the updates-locked window bounded, the snapshot path caps the number of
snapshotted inodes and ranges per fast commit (currently 1024 inodes and 2048
ranges) and falls back to full commit when the cap is exceeded. The series also
handles the journal inode i_data_sem lockdep false positive via subclassing;
journal inode mapping may still take i_data_sem even when data inode mapping is
avoided.
Patch 6 adds the ext4_fc_lock_updates tracepoint to quantify the updates-locked
window and snapshot fallback reasons. Patch 7 extends
/proc/fs/ext4/<sb_id>/fc_info with best-effort snapshot counters. If the /proc
interface is undesirable, I can drop patch 7 and keep the tracepoint only, or
drop even both.
Testing and measurement were done on a QEMU/KVM guest with virtio-pmem + dax
(ext4 -O fast_commit, mounted dax,noatime). The workload does python3 500x
{4K write + fsync}, fallocate 256M, and python3 500x {creat + fsync(dir)}.
Over 3 cold boots, ext4_fc_lock_updates reported locked_ns p50 2.88-2.92 us,
p99 <= 6.71 us, and max <= 102.71 us, with snap_err always 0. Under stress-ng
memory pressure (stress-ng --vm 4 --vm-bytes 75% --timeout 60s), locked_ns p50
2.94 us, p99 <= 4.97 us, and max <= 20.07 us. The fc_info snapshot failure
counters stayed at 0.
These hold times are in the low microseconds range, and the caps keep the
worst case bounded.
Comments and guidance are very welcome. Please let me know if there are any
concerns about correctness, corner cases, or better approaches.
RFC v6 -> RFC v7:
- Rebase onto linux-next master as of 2026-05-09, commit e98d21c170b0
("Add linux-next specific files for 20260508").
- Address Sashiko review feedback for RFC v6. [2]
- Fix the reported snapshot range arithmetic issue near EXT_MAX_BLOCKS to
avoid cur_lblk / range wraparound in the snapshot walk.
- Report successfully snapshotted inode counts in ext4_fc_lock_updates when
snapshotting stops early, as reported by Sashiko.
- Use READ_ONCE() + div64_u64() for the fc_info lock_updates average, as
reported by Sashiko.
RFC v5 -> RFC v6:
- Rebase onto linux-next master as of 2026-04-08.
- Address tracepoint review feedback by relying on enum auto-increment for
snap_err values and by switching the guarded ext4_fc_lock_updates call site
to trace_call__ext4_fc_lock_updates() to avoid the double static_branch. [1]
- Keep lock window accounting unconditional for fc_info while using the guarded
direct tracepoint call.
- Fix the inode debug print format exposed by the rebase.
RFC v4 -> RFC v5:
- Patch 6: Make ext4_fc_lock_updates snap_err human readable via
TRACE_DEFINE_ENUM() + __print_symbolic(), using a single TRACE_SNAP_ERR
mapping while keeping the enum values stable for tooling.
RFC v3 -> RFC v4:
- Replace lockdep_assert movement with removing the wait in
ext4_fc_track_inode() and using EXT4_STATE_FC_REQUEUE to capture updates
during an ongoing fast commit.
- Replace dropping s_fc_lock around log writing with commit-time snapshots of
inode image and mapped ranges (recording the mapped range of tracking as
suggested by Zhang Yi) so log writing consumes only snapshots.
- Avoid inode table I/O under jbd2_journal_lock_updates() via
ext4_get_inode_loc_noio() and fallback to full commit on cache misses.
- Use the extent status cache for snapshot mappings and fall back to full
commit on cache misses or unstable mappings (e.g. delayed allocation).
- Add tracepoint and /proc snapshot stats to quantify the updates-locked window
and snapshot fallback reasons.
RFC v2 -> RFC v3:
- rebase on top of
https://lore.kernel.org/linux-ext4/20251223131342.287864-1-me@linux.beauty/T/#u
RFC v1 -> RFC v2:
- patch 1: move comments to correct place
- patch 2: add it to patchset.
- add missing RFC prefix
RFC v1: https://lore.kernel.org/linux-ext4/20251222032655.87056-1-me@linux.beauty/T/#u
RFC v2: https://lore.kernel.org/linux-ext4/20251222151906.24607-1-me@linux.beauty/T/#t
RFC v3: https://lore.kernel.org/linux-ext4/20251224032943.134063-1-me@linux.beauty/
RFC v4: https://lore.kernel.org/all/20260120112538.132774-1-me@linux.beauty/
RFC v5: https://lore.kernel.org/all/20260317084624.457185-1-me@linux.beauty/t/#u
RFC v6: https://lore.kernel.org/all/20260408112020.716706-1-me@linux.beauty/
[1]: https://lore.kernel.org/all/acZJl8QUYEq8voqQ@BLRRASHENOY1.amd.com/T/#u
[2]: https://sashiko.dev/#/patchset/20260408112020.716706-1-me%40linux.beauty
Thanks,
Li Chen (7):
ext4: fast commit: snapshot inode state before writing log
ext4: lockdep: handle i_data_sem subclassing for special inodes
ext4: fast commit: avoid waiting for FC_COMMITTING
ext4: fast commit: avoid self-deadlock in inode snapshotting
ext4: fast commit: avoid i_data_sem by dropping ext4_map_blocks() in
snapshots
ext4: fast commit: add lock_updates tracepoint
ext4: fast commit: export snapshot stats in fc_info
fs/ext4/ext4.h | 73 +++-
fs/ext4/fast_commit.c | 716 +++++++++++++++++++++++++++++-------
fs/ext4/inode.c | 51 +++
fs/ext4/super.c | 9 +
include/trace/events/ext4.h | 61 +++
5 files changed, 776 insertions(+), 134 deletions(-)
--
2.53.0
^ permalink raw reply
* [RFC v7 1/7] ext4: fast commit: snapshot inode state before writing log
From: Li Chen @ 2026-05-11 8:42 UTC (permalink / raw)
To: Zhang Yi, Theodore Ts'o, Andreas Dilger, Baokun Li, Jan Kara,
Ojaswin Mujoo, Ritesh Harjani (IBM), Zhang Yi, linux-ext4,
linux-kernel
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel
In-Reply-To: <20260511084304.1559557-1-me@linux.beauty>
Fast commit writes inode metadata and data range updates after unlocking
journal updates. New handles can start at that point, so the log writing
path must not look at live inode state.
Add a commit-time per-inode snapshot and populate it while journal updates
are locked and existing handles are drained. Store the snapshot behind
ext4_inode_info->i_fc_snap so ext4_inode_info only grows by one pointer.
The snapshot contains a copy of the on-disk inode plus the data range
records needed for fast commit TLVs.
Snapshotting runs under jbd2_journal_lock_updates(). Avoid triggering I/O
there by using ext4_get_inode_loc_noio() and falling back to full commit
if the inode table block is not present or not uptodate.
Log writing then only serializes the snapshot, so it no longer needs to
call ext4_map_blocks() and take i_data_sem under s_fc_lock. The snapshot
is installed and freed under s_fc_lock and is released from fast commit
cleanup and inode eviction.
Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
Changes in v7:
- Drop the stale i_fc_wait initialization after rebasing onto the new
linux-next base.
Changes in v6:
- Rebase onto linux-next master as of 2026-04-08.
- Fix the inode debug print format after rebasing.
fs/ext4/ext4.h | 22 ++-
fs/ext4/fast_commit.c | 331 +++++++++++++++++++++++++++++++++++-------
fs/ext4/inode.c | 51 +++++++
3 files changed, 352 insertions(+), 52 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 94283a991e5c..e01d00dbc077 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1023,6 +1023,7 @@ enum {
I_DATA_SEM_EA
};
+struct ext4_fc_inode_snap;
/*
* fourth extended file system inode data in memory
@@ -1079,6 +1080,22 @@ struct ext4_inode_info {
/* End of lblk range that needs to be committed in this fast commit */
ext4_lblk_t i_fc_lblk_len;
+ /*
+ * Commit-time fast commit snapshots.
+ *
+ * i_fc_snap is installed and freed under sbi->s_fc_lock. The fast
+ * commit log writing path reads the snapshot under sbi->s_fc_lock while
+ * serializing fast commit TLVs.
+ *
+ * The snapshot lifetime is bounded by EXT4_STATE_FC_COMMITTING and the
+ * corresponding cleanup / eviction paths.
+ *
+ * i_fc_snap points to per-inode snapshot data for fast commit:
+ * - a raw inode snapshot for EXT4_FC_TAG_INODE
+ * - data range records for EXT4_FC_TAG_{ADD,DEL}_RANGE
+ */
+ struct ext4_fc_inode_snap *i_fc_snap;
+
spinlock_t i_raw_lock; /* protects updates to the raw inode */
/*
@@ -3080,8 +3097,9 @@ extern int ext4_file_getattr(struct mnt_idmap *, const struct path *,
struct kstat *, u32, unsigned int);
extern void ext4_dirty_inode(struct inode *, int);
extern int ext4_change_inode_journal_flag(struct inode *, int);
-extern int ext4_get_inode_loc(struct inode *, struct ext4_iloc *);
-extern int ext4_get_fc_inode_loc(struct super_block *sb, unsigned long ino,
+int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc);
+int ext4_get_inode_loc_noio(struct inode *inode, struct ext4_iloc *iloc);
+int ext4_get_fc_inode_loc(struct super_block *sb, unsigned long ino,
struct ext4_iloc *iloc);
extern int ext4_inode_attach_jinode(struct inode *inode);
extern int ext4_can_truncate(struct inode *inode);
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index b3c22636251d..cd4eac4e7dcb 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -56,21 +56,23 @@
* deleted while it is being flushed.
* [2] Flush data buffers to disk and clear "EXT4_STATE_FC_FLUSHING_DATA"
* state.
- * [3] Lock the journal by calling jbd2_journal_lock_updates. This ensures that
- * all the exsiting handles finish and no new handles can start.
- * [4] Mark all the fast commit eligible inodes as undergoing fast commit
- * by setting "EXT4_STATE_FC_COMMITTING" state.
- * [5] Unlock the journal by calling jbd2_journal_unlock_updates. This allows
+ * [3] Lock the journal by calling jbd2_journal_lock_updates(). This ensures
+ * that all the existing handles finish and no new handles can start.
+ * [4] Mark all the fast commit eligible inodes as undergoing fast commit by
+ * setting "EXT4_STATE_FC_COMMITTING" state, and snapshot the inode state
+ * needed for log writing.
+ * [5] Unlock the journal by calling jbd2_journal_unlock_updates(). This allows
* starting of new handles. If new handles try to start an update on
* any of the inodes that are being committed, ext4_fc_track_inode()
* will block until those inodes have finished the fast commit.
* [6] Commit all the directory entry updates in the fast commit space.
- * [7] Commit all the changed inodes in the fast commit space and clear
- * "EXT4_STATE_FC_COMMITTING" for these inodes.
+ * [7] Commit all the changed inodes in the fast commit space.
* [8] Write tail tag (this tag ensures the atomicity, please read the following
* section for more details).
+ * [9] Clear "EXT4_STATE_FC_COMMITTING" and wake up waiters in
+ * ext4_fc_cleanup().
*
- * All the inode updates must be enclosed within jbd2_jounrnal_start()
+ * All the inode updates must be enclosed within jbd2_journal_start()
* and jbd2_journal_stop() similar to JBD2 journaling.
*
* Fast Commit Ineligibility
@@ -200,6 +202,8 @@ static void ext4_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
unlock_buffer(bh);
}
+static void ext4_fc_free_inode_snap(struct inode *inode);
+
static inline void ext4_fc_reset_inode(struct inode *inode)
{
struct ext4_inode_info *ei = EXT4_I(inode);
@@ -216,6 +220,7 @@ void ext4_fc_init_inode(struct inode *inode)
ext4_clear_inode_state(inode, EXT4_STATE_FC_COMMITTING);
INIT_LIST_HEAD(&ei->i_fc_list);
INIT_LIST_HEAD(&ei->i_fc_dilist);
+ ei->i_fc_snap = NULL;
}
static bool ext4_fc_disabled(struct super_block *sb)
@@ -246,6 +251,7 @@ void ext4_fc_del(struct inode *inode)
alloc_ctx = ext4_fc_lock(inode->i_sb);
if (list_empty(&ei->i_fc_list) && list_empty(&ei->i_fc_dilist)) {
+ ext4_fc_free_inode_snap(inode);
ext4_fc_unlock(inode->i_sb, alloc_ctx);
return;
}
@@ -287,6 +293,7 @@ void ext4_fc_del(struct inode *inode)
}
finish_wait(wq, &wait.wq_entry);
}
+ ext4_fc_free_inode_snap(inode);
list_del_init(&ei->i_fc_list);
/*
@@ -829,6 +836,21 @@ static bool ext4_fc_add_dentry_tlv(struct super_block *sb, u32 *crc,
return true;
}
+struct ext4_fc_range {
+ struct list_head list;
+ u16 tag;
+ ext4_lblk_t lblk;
+ ext4_lblk_t len;
+ ext4_fsblk_t pblk;
+ bool unwritten;
+};
+
+struct ext4_fc_inode_snap {
+ struct list_head data_list;
+ unsigned int inode_len;
+ u8 inode_buf[];
+};
+
/*
* Writes inode in the fast commit space under TLV with tag @tag.
* Returns 0 on success, error on failure.
@@ -836,21 +858,21 @@ static bool ext4_fc_add_dentry_tlv(struct super_block *sb, u32 *crc,
static int ext4_fc_write_inode(struct inode *inode, u32 *crc)
{
struct ext4_inode_info *ei = EXT4_I(inode);
- int inode_len = EXT4_GOOD_OLD_INODE_SIZE;
- int ret;
- struct ext4_iloc iloc;
+ struct ext4_fc_inode_snap *snap = ei->i_fc_snap;
struct ext4_fc_inode fc_inode;
struct ext4_fc_tl tl;
u8 *dst;
+ u8 *src;
+ int inode_len;
+ int ret;
- ret = ext4_get_inode_loc(inode, &iloc);
- if (ret)
- return ret;
+ if (!snap)
+ return -ECANCELED;
- if (ext4_test_inode_flag(inode, EXT4_INODE_INLINE_DATA))
- inode_len = EXT4_INODE_SIZE(inode->i_sb);
- else if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE)
- inode_len += ei->i_extra_isize;
+ src = snap->inode_buf;
+ inode_len = snap->inode_len;
+ if (!src || inode_len == 0)
+ return -ECANCELED;
fc_inode.fc_ino = cpu_to_le32(inode->i_ino);
tl.fc_tag = cpu_to_le16(EXT4_FC_TAG_INODE);
@@ -866,10 +888,9 @@ static int ext4_fc_write_inode(struct inode *inode, u32 *crc)
dst += EXT4_FC_TAG_BASE_LEN;
memcpy(dst, &fc_inode, sizeof(fc_inode));
dst += sizeof(fc_inode);
- memcpy(dst, (u8 *)ext4_raw_inode(&iloc), inode_len);
+ memcpy(dst, src, inode_len);
ret = 0;
err:
- brelse(iloc.bh);
return ret;
}
@@ -879,12 +900,74 @@ static int ext4_fc_write_inode(struct inode *inode, u32 *crc)
*/
static int ext4_fc_write_inode_data(struct inode *inode, u32 *crc)
{
- ext4_lblk_t old_blk_size, cur_lblk_off, new_blk_size;
struct ext4_inode_info *ei = EXT4_I(inode);
- struct ext4_map_blocks map;
+ struct ext4_fc_inode_snap *snap = ei->i_fc_snap;
struct ext4_fc_add_range fc_ext;
struct ext4_fc_del_range lrange;
struct ext4_extent *ex;
+ struct ext4_fc_range *range;
+
+ if (!snap)
+ return -ECANCELED;
+
+ list_for_each_entry(range, &snap->data_list, list) {
+ if (range->tag == EXT4_FC_TAG_DEL_RANGE) {
+ lrange.fc_ino = cpu_to_le32(inode->i_ino);
+ lrange.fc_lblk = cpu_to_le32(range->lblk);
+ lrange.fc_len = cpu_to_le32(range->len);
+ if (!ext4_fc_add_tlv(inode->i_sb, EXT4_FC_TAG_DEL_RANGE,
+ sizeof(lrange), (u8 *)&lrange, crc))
+ return -ENOSPC;
+ continue;
+ }
+
+ fc_ext.fc_ino = cpu_to_le32(inode->i_ino);
+ ex = (struct ext4_extent *)&fc_ext.fc_ex;
+ ex->ee_block = cpu_to_le32(range->lblk);
+ ex->ee_len = cpu_to_le16(range->len);
+ ext4_ext_store_pblock(ex, range->pblk);
+ if (range->unwritten)
+ ext4_ext_mark_unwritten(ex);
+ else
+ ext4_ext_mark_initialized(ex);
+
+ if (!ext4_fc_add_tlv(inode->i_sb, EXT4_FC_TAG_ADD_RANGE,
+ sizeof(fc_ext), (u8 *)&fc_ext, crc))
+ return -ENOSPC;
+ }
+
+ return 0;
+}
+
+static void ext4_fc_free_ranges(struct list_head *head)
+{
+ struct ext4_fc_range *range, *range_n;
+
+ list_for_each_entry_safe(range, range_n, head, list) {
+ list_del(&range->list);
+ kfree(range);
+ }
+}
+
+static void ext4_fc_free_inode_snap(struct inode *inode)
+{
+ struct ext4_inode_info *ei = EXT4_I(inode);
+ struct ext4_fc_inode_snap *snap = ei->i_fc_snap;
+
+ if (!snap)
+ return;
+
+ ext4_fc_free_ranges(&snap->data_list);
+ kfree(snap);
+ ei->i_fc_snap = NULL;
+}
+
+static int ext4_fc_snapshot_inode_data(struct inode *inode,
+ struct list_head *ranges)
+{
+ struct ext4_inode_info *ei = EXT4_I(inode);
+ ext4_lblk_t start_lblk, end_lblk, cur_lblk;
+ struct ext4_map_blocks map;
int ret;
spin_lock(&ei->i_fc_lock);
@@ -892,18 +975,21 @@ static int ext4_fc_write_inode_data(struct inode *inode, u32 *crc)
spin_unlock(&ei->i_fc_lock);
return 0;
}
- old_blk_size = ei->i_fc_lblk_start;
- new_blk_size = ei->i_fc_lblk_start + ei->i_fc_lblk_len - 1;
+ start_lblk = ei->i_fc_lblk_start;
+ end_lblk = ei->i_fc_lblk_start + ei->i_fc_lblk_len - 1;
ei->i_fc_lblk_len = 0;
spin_unlock(&ei->i_fc_lock);
- cur_lblk_off = old_blk_size;
- ext4_debug("will try writing %d to %d for inode %llu\n",
- cur_lblk_off, new_blk_size, inode->i_ino);
+ cur_lblk = start_lblk;
+ ext4_debug("snapshot data ranges %u-%u for inode %llu\n",
+ start_lblk, end_lblk,
+ (unsigned long long)inode->i_ino);
+
+ while (cur_lblk <= end_lblk) {
+ struct ext4_fc_range *range;
- while (cur_lblk_off <= new_blk_size) {
- map.m_lblk = cur_lblk_off;
- map.m_len = new_blk_size - cur_lblk_off + 1;
+ map.m_lblk = cur_lblk;
+ map.m_len = end_lblk - cur_lblk + 1;
ret = ext4_map_blocks(NULL, inode, &map,
EXT4_GET_BLOCKS_IO_SUBMIT |
EXT4_EX_NOCACHE);
@@ -911,17 +997,21 @@ static int ext4_fc_write_inode_data(struct inode *inode, u32 *crc)
return -ECANCELED;
if (map.m_len == 0) {
- cur_lblk_off++;
+ cur_lblk++;
continue;
}
+ range = kmalloc(sizeof(*range), GFP_NOFS);
+ if (!range)
+ return -ENOMEM;
+
+ range->lblk = map.m_lblk;
+ range->len = map.m_len;
+ range->pblk = 0;
+ range->unwritten = false;
+
if (ret == 0) {
- lrange.fc_ino = cpu_to_le32(inode->i_ino);
- lrange.fc_lblk = cpu_to_le32(map.m_lblk);
- lrange.fc_len = cpu_to_le32(map.m_len);
- if (!ext4_fc_add_tlv(inode->i_sb, EXT4_FC_TAG_DEL_RANGE,
- sizeof(lrange), (u8 *)&lrange, crc))
- return -ENOSPC;
+ range->tag = EXT4_FC_TAG_DEL_RANGE;
} else {
unsigned int max = (map.m_flags & EXT4_MAP_UNWRITTEN) ?
EXT_UNWRITTEN_MAX_LEN : EXT_INIT_MAX_LEN;
@@ -929,26 +1019,67 @@ static int ext4_fc_write_inode_data(struct inode *inode, u32 *crc)
/* Limit the number of blocks in one extent */
map.m_len = min(max, map.m_len);
- fc_ext.fc_ino = cpu_to_le32(inode->i_ino);
- ex = (struct ext4_extent *)&fc_ext.fc_ex;
- ex->ee_block = cpu_to_le32(map.m_lblk);
- ex->ee_len = cpu_to_le16(map.m_len);
- ext4_ext_store_pblock(ex, map.m_pblk);
- if (map.m_flags & EXT4_MAP_UNWRITTEN)
- ext4_ext_mark_unwritten(ex);
- else
- ext4_ext_mark_initialized(ex);
- if (!ext4_fc_add_tlv(inode->i_sb, EXT4_FC_TAG_ADD_RANGE,
- sizeof(fc_ext), (u8 *)&fc_ext, crc))
- return -ENOSPC;
+ range->tag = EXT4_FC_TAG_ADD_RANGE;
+ range->len = map.m_len;
+ range->pblk = map.m_pblk;
+ range->unwritten = !!(map.m_flags & EXT4_MAP_UNWRITTEN);
}
- cur_lblk_off += map.m_len;
+ INIT_LIST_HEAD(&range->list);
+ list_add_tail(&range->list, ranges);
+
+ cur_lblk += map.m_len;
}
return 0;
}
+static int ext4_fc_snapshot_inode(struct inode *inode)
+{
+ struct ext4_inode_info *ei = EXT4_I(inode);
+ struct ext4_fc_inode_snap *snap;
+ int inode_len = EXT4_GOOD_OLD_INODE_SIZE;
+ struct ext4_iloc iloc;
+ LIST_HEAD(ranges);
+ int ret;
+ int alloc_ctx;
+
+ ret = ext4_get_inode_loc_noio(inode, &iloc);
+ if (ret)
+ return ret;
+
+ if (ext4_test_inode_flag(inode, EXT4_INODE_INLINE_DATA))
+ inode_len = EXT4_INODE_SIZE(inode->i_sb);
+ else if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE)
+ inode_len += ei->i_extra_isize;
+
+ snap = kmalloc(struct_size(snap, inode_buf, inode_len), GFP_NOFS);
+ if (!snap) {
+ brelse(iloc.bh);
+ return -ENOMEM;
+ }
+ INIT_LIST_HEAD(&snap->data_list);
+ snap->inode_len = inode_len;
+
+ memcpy(snap->inode_buf, (u8 *)ext4_raw_inode(&iloc), inode_len);
+ brelse(iloc.bh);
+
+ ret = ext4_fc_snapshot_inode_data(inode, &ranges);
+ if (ret) {
+ kfree(snap);
+ ext4_fc_free_ranges(&ranges);
+ return ret;
+ }
+
+ alloc_ctx = ext4_fc_lock(inode->i_sb);
+ ext4_fc_free_inode_snap(inode);
+ ei->i_fc_snap = snap;
+ list_splice_tail_init(&ranges, &snap->data_list);
+ ext4_fc_unlock(inode->i_sb, alloc_ctx);
+
+ return 0;
+}
+
/* Flushes data of all the inodes in the commit queue. */
static int ext4_fc_flush_data(journal_t *journal)
@@ -999,6 +1130,11 @@ static int ext4_fc_commit_dentry_updates(journal_t *journal, u32 *crc)
*/
if (list_empty(&fc_dentry->fcd_dilist))
continue;
+ /*
+ * For EXT4_FC_TAG_CREAT, fcd_dilist is linked on the created
+ * inode's i_fc_dilist list (kept singular), so we can recover the
+ * inode through it.
+ */
ei = list_first_entry(&fc_dentry->fcd_dilist,
struct ext4_inode_info, i_fc_dilist);
inode = &ei->vfs_inode;
@@ -1023,6 +1159,88 @@ static int ext4_fc_commit_dentry_updates(journal_t *journal, u32 *crc)
return 0;
}
+static int ext4_fc_snapshot_inodes(journal_t *journal)
+{
+ struct super_block *sb = journal->j_private;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+ struct ext4_inode_info *iter;
+ struct ext4_fc_dentry_update *fc_dentry;
+ struct inode **inodes;
+ unsigned int nr_inodes = 0;
+ unsigned int i = 0;
+ int ret = 0;
+ int alloc_ctx;
+
+ alloc_ctx = ext4_fc_lock(sb);
+ list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list)
+ nr_inodes++;
+
+ list_for_each_entry(fc_dentry, &sbi->s_fc_dentry_q[FC_Q_MAIN], fcd_list) {
+ struct ext4_inode_info *ei;
+
+ if (fc_dentry->fcd_op != EXT4_FC_TAG_CREAT)
+ continue;
+ if (list_empty(&fc_dentry->fcd_dilist))
+ continue;
+
+ /* See the comment in ext4_fc_commit_dentry_updates(). */
+ ei = list_first_entry(&fc_dentry->fcd_dilist,
+ struct ext4_inode_info, i_fc_dilist);
+ if (!list_empty(&ei->i_fc_list))
+ continue;
+
+ nr_inodes++;
+ }
+ ext4_fc_unlock(sb, alloc_ctx);
+
+ if (!nr_inodes)
+ return 0;
+
+ inodes = kvcalloc(nr_inodes, sizeof(*inodes), GFP_NOFS);
+ if (!inodes)
+ return -ENOMEM;
+
+ alloc_ctx = ext4_fc_lock(sb);
+ list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
+ inodes[i] = igrab(&iter->vfs_inode);
+ if (inodes[i])
+ i++;
+ }
+
+ list_for_each_entry(fc_dentry, &sbi->s_fc_dentry_q[FC_Q_MAIN], fcd_list) {
+ struct ext4_inode_info *ei;
+
+ if (fc_dentry->fcd_op != EXT4_FC_TAG_CREAT)
+ continue;
+ if (list_empty(&fc_dentry->fcd_dilist))
+ continue;
+
+ /* See the comment in ext4_fc_commit_dentry_updates(). */
+ ei = list_first_entry(&fc_dentry->fcd_dilist,
+ struct ext4_inode_info, i_fc_dilist);
+ if (!list_empty(&ei->i_fc_list))
+ continue;
+
+ inodes[i] = igrab(&ei->vfs_inode);
+ if (inodes[i])
+ i++;
+ }
+ ext4_fc_unlock(sb, alloc_ctx);
+
+ for (nr_inodes = 0; nr_inodes < i; nr_inodes++) {
+ ret = ext4_fc_snapshot_inode(inodes[nr_inodes]);
+ if (ret)
+ break;
+ }
+
+ for (nr_inodes = 0; nr_inodes < i; nr_inodes++) {
+ if (inodes[nr_inodes])
+ iput(inodes[nr_inodes]);
+ }
+ kvfree(inodes);
+ return ret;
+}
+
static int ext4_fc_perform_commit(journal_t *journal)
{
struct super_block *sb = journal->j_private;
@@ -1095,7 +1313,11 @@ static int ext4_fc_perform_commit(journal_t *journal)
EXT4_STATE_FC_COMMITTING);
}
ext4_fc_unlock(sb, alloc_ctx);
+
+ ret = ext4_fc_snapshot_inodes(journal);
jbd2_journal_unlock_updates(journal);
+ if (ret)
+ return ret;
/*
* Step 5: If file system device is different from journal device,
@@ -1292,6 +1514,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
struct ext4_inode_info,
i_fc_list);
list_del_init(&ei->i_fc_list);
+ ext4_fc_free_inode_snap(&ei->vfs_inode);
ext4_clear_inode_state(&ei->vfs_inode,
EXT4_STATE_FC_COMMITTING);
if (tid_geq(tid, ei->i_sync_tid)) {
@@ -1327,6 +1550,14 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
struct ext4_fc_dentry_update,
fcd_list);
list_del_init(&fc_dentry->fcd_list);
+ if (fc_dentry->fcd_op == EXT4_FC_TAG_CREAT &&
+ !list_empty(&fc_dentry->fcd_dilist)) {
+ /* See the comment in ext4_fc_commit_dentry_updates(). */
+ ei = list_first_entry(&fc_dentry->fcd_dilist,
+ struct ext4_inode_info,
+ i_fc_dilist);
+ ext4_fc_free_inode_snap(&ei->vfs_inode);
+ }
list_del_init(&fc_dentry->fcd_dilist);
release_dentry_name_snapshot(&fc_dentry->fcd_name);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c2c2d6ac7f3d..4678612f82e8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5025,6 +5025,57 @@ int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
return ret;
}
+/*
+ * ext4_get_inode_loc_noio() is a best-effort variant of ext4_get_inode_loc().
+ * It looks up the inode table block in the buffer cache and returns -EAGAIN if
+ * the block is not present or not uptodate, without starting any I/O.
+ */
+int ext4_get_inode_loc_noio(struct inode *inode, struct ext4_iloc *iloc)
+{
+ struct super_block *sb = inode->i_sb;
+ struct ext4_group_desc *gdp;
+ struct buffer_head *bh;
+ ext4_fsblk_t block;
+ int inodes_per_block, inode_offset;
+ unsigned long ino = inode->i_ino;
+
+ iloc->bh = NULL;
+ if (ino < EXT4_ROOT_INO ||
+ ino > le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count))
+ return -EFSCORRUPTED;
+
+ iloc->block_group = (ino - 1) / EXT4_INODES_PER_GROUP(sb);
+ gdp = ext4_get_group_desc(sb, iloc->block_group, NULL);
+ if (!gdp)
+ return -EIO;
+
+ /* Figure out the offset within the block group inode table. */
+ inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
+ inode_offset = ((ino - 1) % EXT4_INODES_PER_GROUP(sb));
+ iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);
+
+ block = ext4_inode_table(sb, gdp);
+ if (block <= le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block) ||
+ block >= ext4_blocks_count(EXT4_SB(sb)->s_es)) {
+ ext4_error(sb,
+ "Invalid inode table block %llu in block_group %u",
+ block, iloc->block_group);
+ return -EFSCORRUPTED;
+ }
+ block += inode_offset / inodes_per_block;
+
+ bh = sb_find_get_block(sb, block);
+ if (!bh)
+ return -EAGAIN;
+ if (!ext4_buffer_uptodate(bh)) {
+ brelse(bh);
+ return -EAGAIN;
+ }
+
+ iloc->bh = bh;
+ return 0;
+}
+
int ext4_get_fc_inode_loc(struct super_block *sb, unsigned long ino,
struct ext4_iloc *iloc)
--
2.53.0
^ permalink raw reply related
* [RFC v7 2/7] ext4: lockdep: handle i_data_sem subclassing for special inodes
From: Li Chen @ 2026-05-11 8:42 UTC (permalink / raw)
To: Zhang Yi, Theodore Ts'o, Andreas Dilger, Baokun Li, Jan Kara,
Ojaswin Mujoo, Ritesh Harjani (IBM), Zhang Yi, linux-ext4,
linux-kernel
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel
In-Reply-To: <20260511084304.1559557-1-me@linux.beauty>
Fast commit can hold s_fc_lock while writing journal blocks. Mapping the
journal inode can take its i_data_sem. Normal inode update paths can take a
data inode i_data_sem and then s_fc_lock, which makes lockdep report a
circular dependency.
lockdep treats all i_data_sem instances as one lock class and cannot
distinguish the journal inode i_data_sem from a regular inode i_data_sem.
The journal inode is not tracked by fast commit and no FC waiters ever
depend on it, so this is not a real ABBA deadlock. Assign the journal inode
a dedicated i_data_sem lockdep subclass to avoid the false positive.
Inode cache objects can be recycled, so also reset i_data_sem to
I_DATA_SEM_NORMAL when allocating an ext4 inode. Otherwise a new inode may
inherit an old subclass (journal/quota/ea) and trigger lockdep warnings.
Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
Changes in v6:
- Rebase onto linux-next master as of 2026-04-08.
- Refresh the patch context around upstream ext4_alloc_inode() changes,
without changing the subclassing logic.
fs/ext4/ext4.h | 4 +++-
fs/ext4/super.c | 8 ++++++++
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index e01d00dbc077..05c8f67625b4 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1015,12 +1015,14 @@ do { \
* than the first
* I_DATA_SEM_QUOTA - Used for quota inodes only
* I_DATA_SEM_EA - Used for ea_inodes only
+ * I_DATA_SEM_JOURNAL - Used for journal inode only
*/
enum {
I_DATA_SEM_NORMAL = 0,
I_DATA_SEM_OTHER,
I_DATA_SEM_QUOTA,
- I_DATA_SEM_EA
+ I_DATA_SEM_EA,
+ I_DATA_SEM_JOURNAL
};
struct ext4_fc_inode_snap;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 6a77db4d3124..3c869f0001c5 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1431,6 +1431,9 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
ext4_fc_init_inode(&ei->vfs_inode);
spin_lock_init(&ei->i_fc_lock);
mmb_init(&ei->i_metadata_bhs, &ei->vfs_inode.i_data);
+#ifdef CONFIG_LOCKDEP
+ lockdep_set_subclass(&ei->i_data_sem, I_DATA_SEM_NORMAL);
+#endif
return &ei->vfs_inode;
}
@@ -5910,6 +5913,11 @@ static struct inode *ext4_get_journal_inode(struct super_block *sb,
return ERR_PTR(-EFSCORRUPTED);
}
+#ifdef CONFIG_LOCKDEP
+ lockdep_set_subclass(&EXT4_I(journal_inode)->i_data_sem,
+ I_DATA_SEM_JOURNAL);
+#endif
+
ext4_debug("Journal inode found at %p: %lld bytes\n",
journal_inode, journal_inode->i_size);
return journal_inode;
--
2.53.0
^ permalink raw reply related
* [RFC v7 3/7] ext4: fast commit: avoid waiting for FC_COMMITTING
From: Li Chen @ 2026-05-11 8:42 UTC (permalink / raw)
To: Zhang Yi, Theodore Ts'o, Andreas Dilger, Baokun Li, Jan Kara,
Ojaswin Mujoo, Ritesh Harjani (IBM), Zhang Yi, linux-ext4,
linux-kernel
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel
In-Reply-To: <20260511084304.1559557-1-me@linux.beauty>
ext4_fc_track_inode() can be called while holding i_data_sem (e.g.
fallocate). Waiting for EXT4_STATE_FC_COMMITTING in that case risks an
ABBA deadlock: i_data_sem -> wait(FC_COMMITTING) vs FC_COMMITTING ->
wait(i_data_sem) in the commit task.
Now that fast commit snapshots inode state at commit time, updates during
log writing do not need to block. Drop the wait and lockdep assertion in
ext4_fc_track_inode(), and make ext4_fc_del() wait for FC_COMMITTING so an
inode cannot be removed while the commit thread is still using it.
When an inode is modified during a fast commit, mark it with
EXT4_STATE_FC_REQUEUE so cleanup keeps it queued for the next fast commit.
This is needed because jbd2_fc_end_commit() invokes the cleanup callback
with tid == 0, so tid-based requeue logic would requeue every inode.
Testing: tracepoint ext4:ext4_fc_commit_stop with two fsyncs in the same
transaction. nblks is the number of journal blocks written for that fast
commit. Before this change, the second fsync still wrote almost the same
fast commit log (nblks 10->9), because tid == 0 in jbd2_fc_end_commit()
caused the tid-based requeue logic to keep all inodes queued. After this
change, only inodes modified during the commit are requeued, and the
second fsync wrote a nearly empty fast commit (nblks 10->1).
Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
fs/ext4/ext4.h | 1 +
fs/ext4/fast_commit.c | 111 ++++++++++++++++++++----------------------
2 files changed, 53 insertions(+), 59 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 05c8f67625b4..2a706acdfaf8 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1991,6 +1991,7 @@ enum {
EXT4_STATE_FC_COMMITTING, /* Fast commit ongoing */
EXT4_STATE_FC_FLUSHING_DATA, /* Fast commit flushing data */
EXT4_STATE_ORPHAN_FILE, /* Inode orphaned in orphan file */
+ EXT4_STATE_FC_REQUEUE, /* Inode modified during fast commit */
};
#define EXT4_INODE_BIT_FNS(name, field, offset) \
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index cd4eac4e7dcb..273bf34031ae 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -62,9 +62,8 @@
* setting "EXT4_STATE_FC_COMMITTING" state, and snapshot the inode state
* needed for log writing.
* [5] Unlock the journal by calling jbd2_journal_unlock_updates(). This allows
- * starting of new handles. If new handles try to start an update on
- * any of the inodes that are being committed, ext4_fc_track_inode()
- * will block until those inodes have finished the fast commit.
+ * starting of new handles. Updates to inodes being fast committed are
+ * tracked for requeue rather than blocking.
* [6] Commit all the directory entry updates in the fast commit space.
* [7] Commit all the changed inodes in the fast commit space.
* [8] Write tail tag (this tag ensures the atomicity, please read the following
@@ -218,6 +217,7 @@ void ext4_fc_init_inode(struct inode *inode)
ext4_fc_reset_inode(inode);
ext4_clear_inode_state(inode, EXT4_STATE_FC_COMMITTING);
+ ext4_clear_inode_state(inode, EXT4_STATE_FC_REQUEUE);
INIT_LIST_HEAD(&ei->i_fc_list);
INIT_LIST_HEAD(&ei->i_fc_dilist);
ei->i_fc_snap = NULL;
@@ -257,22 +257,30 @@ void ext4_fc_del(struct inode *inode)
}
/*
- * Since ext4_fc_del is called from ext4_evict_inode while having a
- * handle open, there is no need for us to wait here even if a fast
- * commit is going on. That is because, if this inode is being
- * committed, ext4_mark_inode_dirty would have waited for inode commit
- * operation to finish before we come here. So, by the time we come
- * here, inode's EXT4_STATE_FC_COMMITTING would have been cleared. So,
- * we shouldn't see EXT4_STATE_FC_COMMITTING to be set on this inode
- * here.
- *
- * We may come here without any handles open in the "no_delete" case of
- * ext4_evict_inode as well. However, if that happens, we first mark the
- * file system as fast commit ineligible anyway. So, even in that case,
- * it is okay to remove the inode from the fc list.
+ * Wait for ongoing fast commit to finish. We cannot remove the inode
+ * from fast commit lists while it is being committed.
*/
- WARN_ON(ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)
- && !ext4_test_mount_flag(inode->i_sb, EXT4_MF_FC_INELIGIBLE));
+ while (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)) {
+#if (BITS_PER_LONG < 64)
+ DEFINE_WAIT_BIT(wait, &ei->i_state_flags,
+ EXT4_STATE_FC_COMMITTING);
+ wq = bit_waitqueue(&ei->i_state_flags,
+ EXT4_STATE_FC_COMMITTING);
+#else
+ DEFINE_WAIT_BIT(wait, &ei->i_flags,
+ EXT4_STATE_FC_COMMITTING);
+ wq = bit_waitqueue(&ei->i_flags,
+ EXT4_STATE_FC_COMMITTING);
+#endif
+ prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
+ if (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)) {
+ ext4_fc_unlock(inode->i_sb, alloc_ctx);
+ schedule();
+ alloc_ctx = ext4_fc_lock(inode->i_sb);
+ }
+ finish_wait(wq, &wait.wq_entry);
+ }
+
while (ext4_test_inode_state(inode, EXT4_STATE_FC_FLUSHING_DATA)) {
#if (BITS_PER_LONG < 64)
DEFINE_WAIT_BIT(wait, &ei->i_state_flags,
@@ -293,19 +301,22 @@ void ext4_fc_del(struct inode *inode)
}
finish_wait(wq, &wait.wq_entry);
}
+
ext4_fc_free_inode_snap(inode);
list_del_init(&ei->i_fc_list);
/*
- * Since this inode is getting removed, let's also remove all FC
- * dentry create references, since it is not needed to log it anyways.
+ * Since this inode is getting removed, let's also remove all FC dentry
+ * create references, since it is not needed to log it anyways.
*/
if (list_empty(&ei->i_fc_dilist)) {
ext4_fc_unlock(inode->i_sb, alloc_ctx);
return;
}
- fc_dentry = list_first_entry(&ei->i_fc_dilist, struct ext4_fc_dentry_update, fcd_dilist);
+ fc_dentry = list_first_entry(&ei->i_fc_dilist,
+ struct ext4_fc_dentry_update,
+ fcd_dilist);
WARN_ON(fc_dentry->fcd_op != EXT4_FC_TAG_CREAT);
list_del_init(&fc_dentry->fcd_list);
list_del_init(&fc_dentry->fcd_dilist);
@@ -377,6 +388,8 @@ static int ext4_fc_track_template(
tid = handle->h_transaction->t_tid;
spin_lock(&ei->i_fc_lock);
+ if (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING))
+ ext4_set_inode_state(inode, EXT4_STATE_FC_REQUEUE);
if (tid == ei->i_sync_tid) {
update = true;
} else {
@@ -547,8 +560,6 @@ static int __track_inode(handle_t *handle, struct inode *inode, void *arg,
void ext4_fc_track_inode(handle_t *handle, struct inode *inode)
{
- struct ext4_inode_info *ei = EXT4_I(inode);
- wait_queue_head_t *wq;
int ret;
if (S_ISDIR(inode->i_mode))
@@ -564,29 +575,11 @@ void ext4_fc_track_inode(handle_t *handle, struct inode *inode)
return;
/*
- * If we come here, we may sleep while waiting for the inode to
- * commit. We shouldn't be holding i_data_sem when we go to sleep since
- * the commit path needs to grab the lock while committing the inode.
+ * Fast commit snapshots inode state at commit time, so there's no need
+ * to wait for EXT4_STATE_FC_COMMITTING here. If the inode is already
+ * on the commit queue, ext4_fc_cleanup() will requeue it for the new
+ * transaction once the current commit finishes.
*/
- lockdep_assert_not_held(&ei->i_data_sem);
-
- while (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)) {
-#if (BITS_PER_LONG < 64)
- DEFINE_WAIT_BIT(wait, &ei->i_state_flags,
- EXT4_STATE_FC_COMMITTING);
- wq = bit_waitqueue(&ei->i_state_flags,
- EXT4_STATE_FC_COMMITTING);
-#else
- DEFINE_WAIT_BIT(wait, &ei->i_flags,
- EXT4_STATE_FC_COMMITTING);
- wq = bit_waitqueue(&ei->i_flags,
- EXT4_STATE_FC_COMMITTING);
-#endif
- prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
- if (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING))
- schedule();
- finish_wait(wq, &wait.wq_entry);
- }
/*
* From this point on, this inode will not be committed either
@@ -1510,32 +1503,32 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
alloc_ctx = ext4_fc_lock(sb);
while (!list_empty(&sbi->s_fc_q[FC_Q_MAIN])) {
+ bool requeue;
+
ei = list_first_entry(&sbi->s_fc_q[FC_Q_MAIN],
struct ext4_inode_info,
i_fc_list);
list_del_init(&ei->i_fc_list);
ext4_fc_free_inode_snap(&ei->vfs_inode);
+ spin_lock(&ei->i_fc_lock);
+ if (full)
+ requeue = !tid_geq(tid, ei->i_sync_tid);
+ else
+ requeue = ext4_test_inode_state(&ei->vfs_inode,
+ EXT4_STATE_FC_REQUEUE);
+ if (!requeue)
+ ext4_fc_reset_inode(&ei->vfs_inode);
+ ext4_clear_inode_state(&ei->vfs_inode, EXT4_STATE_FC_REQUEUE);
ext4_clear_inode_state(&ei->vfs_inode,
EXT4_STATE_FC_COMMITTING);
- if (tid_geq(tid, ei->i_sync_tid)) {
- ext4_fc_reset_inode(&ei->vfs_inode);
- } else if (full) {
- /*
- * We are called after a full commit, inode has been
- * modified while the commit was running. Re-enqueue
- * the inode into STAGING, which will then be splice
- * back into MAIN. This cannot happen during
- * fastcommit because the journal is locked all the
- * time in that case (and tid doesn't increase so
- * tid check above isn't reliable).
- */
+ spin_unlock(&ei->i_fc_lock);
+ if (requeue)
list_add_tail(&ei->i_fc_list,
&sbi->s_fc_q[FC_Q_STAGING]);
- }
/*
* Make sure clearing of EXT4_STATE_FC_COMMITTING is
* visible before we send the wakeup. Pairs with implicit
- * barrier in prepare_to_wait() in ext4_fc_track_inode().
+ * barrier in prepare_to_wait() in ext4_fc_del().
*/
smp_mb();
#if (BITS_PER_LONG < 64)
--
2.53.0
^ permalink raw reply related
* [RFC v7 4/7] ext4: fast commit: avoid self-deadlock in inode snapshotting
From: Li Chen @ 2026-05-11 8:42 UTC (permalink / raw)
To: Zhang Yi, Theodore Ts'o, Andreas Dilger, Baokun Li, Jan Kara,
Ojaswin Mujoo, Ritesh Harjani (IBM), Zhang Yi, linux-ext4,
linux-kernel
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel
In-Reply-To: <20260511084304.1559557-1-me@linux.beauty>
ext4_fc_snapshot_inodes() used igrab()/iput() to pin inodes while building
commit-time snapshots. With ext4_fc_del() waiting for
EXT4_STATE_FC_COMMITTING, iput() can trigger
ext4_clear_inode()->ext4_fc_del() in the commit thread and deadlock waiting
for the fast commit to finish.
Avoid taking extra references. Collect inode pointers under s_fc_lock and
rely on EXT4_STATE_FC_COMMITTING to pin inodes until ext4_fc_cleanup()
clears the bit.
Also set EXT4_STATE_FC_COMMITTING for create-only inodes referenced
from the dentry update queue, and wake up waiters when ext4_fc_cleanup()
clears the bit.
Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
fs/ext4/fast_commit.c | 47 ++++++++++++++++++++++++++++++++-----------
1 file changed, 35 insertions(+), 12 deletions(-)
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 273bf34031ae..f9bb18c0b549 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -1195,13 +1195,12 @@ static int ext4_fc_snapshot_inodes(journal_t *journal)
alloc_ctx = ext4_fc_lock(sb);
list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
- inodes[i] = igrab(&iter->vfs_inode);
- if (inodes[i])
- i++;
+ inodes[i++] = &iter->vfs_inode;
}
list_for_each_entry(fc_dentry, &sbi->s_fc_dentry_q[FC_Q_MAIN], fcd_list) {
struct ext4_inode_info *ei;
+ struct inode *inode;
if (fc_dentry->fcd_op != EXT4_FC_TAG_CREAT)
continue;
@@ -1211,12 +1210,20 @@ static int ext4_fc_snapshot_inodes(journal_t *journal)
/* See the comment in ext4_fc_commit_dentry_updates(). */
ei = list_first_entry(&fc_dentry->fcd_dilist,
struct ext4_inode_info, i_fc_dilist);
+ inode = &ei->vfs_inode;
if (!list_empty(&ei->i_fc_list))
continue;
- inodes[i] = igrab(&ei->vfs_inode);
- if (inodes[i])
- i++;
+ /*
+ * Create-only inodes may only be referenced via fcd_dilist and
+ * not appear on s_fc_q[MAIN]. They may hit the last iput while
+ * we are snapshotting, but inode eviction calls ext4_fc_del(),
+ * which waits for FC_COMMITTING to clear. Mark them FC_COMMITTING
+ * so the inode stays pinned and the snapshot stays valid until
+ * ext4_fc_cleanup().
+ */
+ ext4_set_inode_state(inode, EXT4_STATE_FC_COMMITTING);
+ inodes[i++] = inode;
}
ext4_fc_unlock(sb, alloc_ctx);
@@ -1226,10 +1233,6 @@ static int ext4_fc_snapshot_inodes(journal_t *journal)
break;
}
- for (nr_inodes = 0; nr_inodes < i; nr_inodes++) {
- if (inodes[nr_inodes])
- iput(inodes[nr_inodes]);
- }
kvfree(inodes);
return ret;
}
@@ -1297,8 +1300,9 @@ static int ext4_fc_perform_commit(journal_t *journal)
jbd2_journal_lock_updates(journal);
/*
* The journal is now locked. No more handles can start and all the
- * previous handles are now drained. We now mark the inodes on the
- * commit queue as being committed.
+ * previous handles are now drained. Snapshotting happens in this
+ * window so log writing can consume only stable snapshots without
+ * doing logical-to-physical mapping.
*/
alloc_ctx = ext4_fc_lock(sb);
list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
@@ -1550,6 +1554,25 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
struct ext4_inode_info,
i_fc_dilist);
ext4_fc_free_inode_snap(&ei->vfs_inode);
+ spin_lock(&ei->i_fc_lock);
+ ext4_clear_inode_state(&ei->vfs_inode,
+ EXT4_STATE_FC_REQUEUE);
+ ext4_clear_inode_state(&ei->vfs_inode,
+ EXT4_STATE_FC_COMMITTING);
+ spin_unlock(&ei->i_fc_lock);
+ /*
+ * Make sure clearing of EXT4_STATE_FC_COMMITTING is
+ * visible before we send the wakeup. Pairs with implicit
+ * barrier in prepare_to_wait() in ext4_fc_del().
+ */
+ smp_mb();
+#if (BITS_PER_LONG < 64)
+ wake_up_bit(&ei->i_state_flags,
+ EXT4_STATE_FC_COMMITTING);
+#else
+ wake_up_bit(&ei->i_flags,
+ EXT4_STATE_FC_COMMITTING);
+#endif
}
list_del_init(&fc_dentry->fcd_dilist);
--
2.53.0
^ permalink raw reply related
* [RFC v7 5/7] ext4: fast commit: avoid i_data_sem by dropping ext4_map_blocks() in snapshots
From: Li Chen @ 2026-05-11 8:43 UTC (permalink / raw)
To: Zhang Yi, Theodore Ts'o, Andreas Dilger, Baokun Li, Jan Kara,
Ojaswin Mujoo, Ritesh Harjani (IBM), Zhang Yi, linux-ext4,
linux-kernel
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel
In-Reply-To: <20260511084304.1559557-1-me@linux.beauty>
Commit-time snapshots run under jbd2_journal_lock_updates(), so the work
done there must stay bounded.
The snapshot path still used ext4_map_blocks() to build data ranges. This
can take i_data_sem and pulls the mapping code into the snapshot logic.
Build inode data range snapshots from the extent status tree instead.
The extent status tree is a cache, not an authoritative source. If the
needed information is missing or unstable (e.g. delayed allocation), treat
the transaction as fast commit ineligible and fall back to full commit.
Also cap the number of inodes and ranges snapshotted per fast commit and
allocate range records from a dedicated slab cache. The inode pointer
array is allocated outside the updates-locked window.
Testing: QEMU/KVM guest, virtio-pmem + dax, ext4 -O fast_commit, mounted
dax,noatime. Ran python3 500x {4K write + fsync}, fallocate 256M, and
python3 500x {creat + fsync(dir)} without lockdep splats or errors.
Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
Changes in v7:
- Address Sashiko review by guarding snapshot range arithmetic near
EXT_MAX_BLOCKS to avoid cur_lblk / remaining-range wraparound in the
snapshot walk.
fs/ext4/fast_commit.c | 257 +++++++++++++++++++++++++++++-------------
1 file changed, 181 insertions(+), 76 deletions(-)
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index f9bb18c0b549..9fc17c1fa7af 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -184,6 +184,15 @@
#include <trace/events/ext4.h>
static struct kmem_cache *ext4_fc_dentry_cachep;
+static struct kmem_cache *ext4_fc_range_cachep;
+
+/*
+ * Avoid spending unbounded time/memory snapshotting highly fragmented files
+ * under jbd2_journal_lock_updates(). If we exceed this limit, fall back to
+ * full commit.
+ */
+#define EXT4_FC_SNAPSHOT_MAX_INODES 1024
+#define EXT4_FC_SNAPSHOT_MAX_RANGES 2048
static void ext4_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
{
@@ -938,7 +947,7 @@ static void ext4_fc_free_ranges(struct list_head *head)
list_for_each_entry_safe(range, range_n, head, list) {
list_del(&range->list);
- kfree(range);
+ kmem_cache_free(ext4_fc_range_cachep, range);
}
}
@@ -956,16 +965,19 @@ static void ext4_fc_free_inode_snap(struct inode *inode)
}
static int ext4_fc_snapshot_inode_data(struct inode *inode,
- struct list_head *ranges)
+ struct list_head *ranges,
+ unsigned int nr_ranges_total,
+ unsigned int *nr_rangesp)
{
struct ext4_inode_info *ei = EXT4_I(inode);
+ unsigned int nr_ranges = 0;
ext4_lblk_t start_lblk, end_lblk, cur_lblk;
- struct ext4_map_blocks map;
- int ret;
spin_lock(&ei->i_fc_lock);
if (ei->i_fc_lblk_len == 0) {
spin_unlock(&ei->i_fc_lock);
+ if (nr_rangesp)
+ *nr_rangesp = 0;
return 0;
}
start_lblk = ei->i_fc_lblk_start;
@@ -979,61 +991,82 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
(unsigned long long)inode->i_ino);
while (cur_lblk <= end_lblk) {
+ struct extent_status es;
struct ext4_fc_range *range;
+ ext4_lblk_t len;
+ u64 remaining = (u64)end_lblk - cur_lblk + 1;
- map.m_lblk = cur_lblk;
- map.m_len = end_lblk - cur_lblk + 1;
- ret = ext4_map_blocks(NULL, inode, &map,
- EXT4_GET_BLOCKS_IO_SUBMIT |
- EXT4_EX_NOCACHE);
- if (ret < 0)
- return -ECANCELED;
+ if (!ext4_es_lookup_extent(inode, cur_lblk, NULL, &es, NULL))
+ return -EAGAIN;
+
+ if (ext4_es_is_delayed(&es))
+ return -EAGAIN;
- if (map.m_len == 0) {
+ len = es.es_len - (cur_lblk - es.es_lblk);
+ if (len > remaining)
+ len = remaining;
+ if (len == 0) {
cur_lblk++;
continue;
}
- range = kmalloc(sizeof(*range), GFP_NOFS);
+ if (nr_ranges_total + nr_ranges >= EXT4_FC_SNAPSHOT_MAX_RANGES)
+ return -E2BIG;
+
+ range = kmem_cache_alloc(ext4_fc_range_cachep, GFP_NOFS);
if (!range)
return -ENOMEM;
+ nr_ranges++;
- range->lblk = map.m_lblk;
- range->len = map.m_len;
+ range->lblk = cur_lblk;
+ range->len = len;
range->pblk = 0;
range->unwritten = false;
- if (ret == 0) {
+ if (ext4_es_is_hole(&es)) {
range->tag = EXT4_FC_TAG_DEL_RANGE;
- } else {
- unsigned int max = (map.m_flags & EXT4_MAP_UNWRITTEN) ?
- EXT_UNWRITTEN_MAX_LEN : EXT_INIT_MAX_LEN;
-
- /* Limit the number of blocks in one extent */
- map.m_len = min(max, map.m_len);
+ } else if (ext4_es_is_written(&es) ||
+ ext4_es_is_unwritten(&es)) {
+ unsigned int max;
range->tag = EXT4_FC_TAG_ADD_RANGE;
- range->len = map.m_len;
- range->pblk = map.m_pblk;
- range->unwritten = !!(map.m_flags & EXT4_MAP_UNWRITTEN);
+ range->pblk = ext4_es_pblock(&es) +
+ (cur_lblk - es.es_lblk);
+ range->unwritten = ext4_es_is_unwritten(&es);
+
+ max = range->unwritten ? EXT_UNWRITTEN_MAX_LEN :
+ EXT_INIT_MAX_LEN;
+ if (range->len > max)
+ range->len = max;
+ } else {
+ kmem_cache_free(ext4_fc_range_cachep, range);
+ return -EAGAIN;
}
INIT_LIST_HEAD(&range->list);
list_add_tail(&range->list, ranges);
- cur_lblk += map.m_len;
+ if ((u64)range->len > (u64)end_lblk - cur_lblk)
+ break;
+
+ cur_lblk += range->len;
}
+ if (nr_rangesp)
+ *nr_rangesp = nr_ranges;
return 0;
}
-static int ext4_fc_snapshot_inode(struct inode *inode)
+static int ext4_fc_snapshot_inode(struct inode *inode,
+ unsigned int nr_ranges_total,
+ unsigned int *nr_rangesp)
{
struct ext4_inode_info *ei = EXT4_I(inode);
struct ext4_fc_inode_snap *snap;
int inode_len = EXT4_GOOD_OLD_INODE_SIZE;
struct ext4_iloc iloc;
LIST_HEAD(ranges);
+ unsigned int nr_ranges = 0;
int ret;
int alloc_ctx;
@@ -1057,7 +1090,8 @@ static int ext4_fc_snapshot_inode(struct inode *inode)
memcpy(snap->inode_buf, (u8 *)ext4_raw_inode(&iloc), inode_len);
brelse(iloc.bh);
- ret = ext4_fc_snapshot_inode_data(inode, &ranges);
+ ret = ext4_fc_snapshot_inode_data(inode, &ranges, nr_ranges_total,
+ &nr_ranges);
if (ret) {
kfree(snap);
ext4_fc_free_ranges(&ranges);
@@ -1070,10 +1104,11 @@ static int ext4_fc_snapshot_inode(struct inode *inode)
list_splice_tail_init(&ranges, &snap->data_list);
ext4_fc_unlock(inode->i_sb, alloc_ctx);
+ if (nr_rangesp)
+ *nr_rangesp = nr_ranges;
return 0;
}
-
/* Flushes data of all the inodes in the commit queue. */
static int ext4_fc_flush_data(journal_t *journal)
{
@@ -1152,49 +1187,32 @@ static int ext4_fc_commit_dentry_updates(journal_t *journal, u32 *crc)
return 0;
}
-static int ext4_fc_snapshot_inodes(journal_t *journal)
+static int ext4_fc_alloc_snapshot_inodes(struct super_block *sb,
+ struct inode ***inodesp,
+ unsigned int *nr_inodesp);
+
+static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes,
+ unsigned int inodes_size)
{
struct super_block *sb = journal->j_private;
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_inode_info *iter;
struct ext4_fc_dentry_update *fc_dentry;
- struct inode **inodes;
- unsigned int nr_inodes = 0;
unsigned int i = 0;
+ unsigned int idx;
+ unsigned int nr_ranges = 0;
int ret = 0;
int alloc_ctx;
- alloc_ctx = ext4_fc_lock(sb);
- list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list)
- nr_inodes++;
-
- list_for_each_entry(fc_dentry, &sbi->s_fc_dentry_q[FC_Q_MAIN], fcd_list) {
- struct ext4_inode_info *ei;
-
- if (fc_dentry->fcd_op != EXT4_FC_TAG_CREAT)
- continue;
- if (list_empty(&fc_dentry->fcd_dilist))
- continue;
-
- /* See the comment in ext4_fc_commit_dentry_updates(). */
- ei = list_first_entry(&fc_dentry->fcd_dilist,
- struct ext4_inode_info, i_fc_dilist);
- if (!list_empty(&ei->i_fc_list))
- continue;
-
- nr_inodes++;
- }
- ext4_fc_unlock(sb, alloc_ctx);
-
- if (!nr_inodes)
+ if (!inodes_size)
return 0;
- inodes = kvcalloc(nr_inodes, sizeof(*inodes), GFP_NOFS);
- if (!inodes)
- return -ENOMEM;
-
alloc_ctx = ext4_fc_lock(sb);
list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
+ if (i >= inodes_size) {
+ ret = -E2BIG;
+ goto unlock;
+ }
inodes[i++] = &iter->vfs_inode;
}
@@ -1214,6 +1232,10 @@ static int ext4_fc_snapshot_inodes(journal_t *journal)
if (!list_empty(&ei->i_fc_list))
continue;
+ if (i >= inodes_size) {
+ ret = -E2BIG;
+ goto unlock;
+ }
/*
* Create-only inodes may only be referenced via fcd_dilist and
* not appear on s_fc_q[MAIN]. They may hit the last iput while
@@ -1225,15 +1247,22 @@ static int ext4_fc_snapshot_inodes(journal_t *journal)
ext4_set_inode_state(inode, EXT4_STATE_FC_COMMITTING);
inodes[i++] = inode;
}
+unlock:
ext4_fc_unlock(sb, alloc_ctx);
- for (nr_inodes = 0; nr_inodes < i; nr_inodes++) {
- ret = ext4_fc_snapshot_inode(inodes[nr_inodes]);
+ if (ret)
+ return ret;
+
+ for (idx = 0; idx < i; idx++) {
+ unsigned int inode_ranges = 0;
+
+ ret = ext4_fc_snapshot_inode(inodes[idx], nr_ranges,
+ &inode_ranges);
if (ret)
break;
+ nr_ranges += inode_ranges;
}
- kvfree(inodes);
return ret;
}
@@ -1244,6 +1273,8 @@ static int ext4_fc_perform_commit(journal_t *journal)
struct ext4_inode_info *iter;
struct ext4_fc_head head;
struct inode *inode;
+ struct inode **inodes;
+ unsigned int inodes_size;
struct blk_plug plug;
int ret = 0;
u32 crc = 0;
@@ -1296,6 +1327,10 @@ static int ext4_fc_perform_commit(journal_t *journal)
return ret;
+ ret = ext4_fc_alloc_snapshot_inodes(sb, &inodes, &inodes_size);
+ if (ret)
+ return ret;
+
/* Step 4: Mark all inodes as being committed. */
jbd2_journal_lock_updates(journal);
/*
@@ -1311,8 +1346,9 @@ static int ext4_fc_perform_commit(journal_t *journal)
}
ext4_fc_unlock(sb, alloc_ctx);
- ret = ext4_fc_snapshot_inodes(journal);
+ ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size);
jbd2_journal_unlock_updates(journal);
+ kvfree(inodes);
if (ret)
return ret;
@@ -1368,6 +1404,64 @@ static int ext4_fc_perform_commit(journal_t *journal)
return ret;
}
+static unsigned int ext4_fc_count_snapshot_inodes(struct super_block *sb)
+{
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+ struct ext4_inode_info *iter;
+ struct ext4_fc_dentry_update *fc_dentry;
+ unsigned int nr_inodes = 0;
+ int alloc_ctx;
+
+ alloc_ctx = ext4_fc_lock(sb);
+ list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list)
+ nr_inodes++;
+
+ list_for_each_entry(fc_dentry, &sbi->s_fc_dentry_q[FC_Q_MAIN], fcd_list) {
+ struct ext4_inode_info *ei;
+
+ if (fc_dentry->fcd_op != EXT4_FC_TAG_CREAT)
+ continue;
+ if (list_empty(&fc_dentry->fcd_dilist))
+ continue;
+
+ /* See the comment in ext4_fc_commit_dentry_updates(). */
+ ei = list_first_entry(&fc_dentry->fcd_dilist,
+ struct ext4_inode_info, i_fc_dilist);
+ if (!list_empty(&ei->i_fc_list))
+ continue;
+
+ nr_inodes++;
+ }
+ ext4_fc_unlock(sb, alloc_ctx);
+
+ return nr_inodes;
+}
+
+static int ext4_fc_alloc_snapshot_inodes(struct super_block *sb,
+ struct inode ***inodesp,
+ unsigned int *nr_inodesp)
+{
+ unsigned int nr_inodes = ext4_fc_count_snapshot_inodes(sb);
+ struct inode **inodes;
+
+ *inodesp = NULL;
+ *nr_inodesp = 0;
+
+ if (!nr_inodes)
+ return 0;
+
+ if (nr_inodes > EXT4_FC_SNAPSHOT_MAX_INODES)
+ return -E2BIG;
+
+ inodes = kvcalloc(nr_inodes, sizeof(*inodes), GFP_NOFS);
+ if (!inodes)
+ return -ENOMEM;
+
+ *inodesp = inodes;
+ *nr_inodesp = nr_inodes;
+ return 0;
+}
+
static void ext4_fc_update_stats(struct super_block *sb, int status,
u64 commit_time, int nblks, tid_t commit_tid)
{
@@ -1460,7 +1554,10 @@ int ext4_fc_commit(journal_t *journal, tid_t commit_tid)
fc_bufs_before = (sbi->s_fc_bytes + bsize - 1) / bsize;
ret = ext4_fc_perform_commit(journal);
if (ret < 0) {
- status = EXT4_FC_STATUS_FAILED;
+ if (ret == -EAGAIN || ret == -E2BIG || ret == -ECANCELED)
+ status = EXT4_FC_STATUS_INELIGIBLE;
+ else
+ status = EXT4_FC_STATUS_FAILED;
goto fallback;
}
nblks = (sbi->s_fc_bytes + bsize - 1) / bsize - fc_bufs_before;
@@ -1544,34 +1641,35 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
while (!list_empty(&sbi->s_fc_dentry_q[FC_Q_MAIN])) {
fc_dentry = list_first_entry(&sbi->s_fc_dentry_q[FC_Q_MAIN],
- struct ext4_fc_dentry_update,
- fcd_list);
+ struct ext4_fc_dentry_update,
+ fcd_list);
list_del_init(&fc_dentry->fcd_list);
if (fc_dentry->fcd_op == EXT4_FC_TAG_CREAT &&
- !list_empty(&fc_dentry->fcd_dilist)) {
+ !list_empty(&fc_dentry->fcd_dilist)) {
/* See the comment in ext4_fc_commit_dentry_updates(). */
ei = list_first_entry(&fc_dentry->fcd_dilist,
- struct ext4_inode_info,
- i_fc_dilist);
+ struct ext4_inode_info,
+ i_fc_dilist);
ext4_fc_free_inode_snap(&ei->vfs_inode);
spin_lock(&ei->i_fc_lock);
ext4_clear_inode_state(&ei->vfs_inode,
- EXT4_STATE_FC_REQUEUE);
+ EXT4_STATE_FC_REQUEUE);
ext4_clear_inode_state(&ei->vfs_inode,
- EXT4_STATE_FC_COMMITTING);
+ EXT4_STATE_FC_COMMITTING);
spin_unlock(&ei->i_fc_lock);
/*
* Make sure clearing of EXT4_STATE_FC_COMMITTING is
- * visible before we send the wakeup. Pairs with implicit
- * barrier in prepare_to_wait() in ext4_fc_del().
+ * visible before we send the wakeup. Pairs with
+ * implicit barrier in prepare_to_wait() in
+ * ext4_fc_del().
*/
smp_mb();
#if (BITS_PER_LONG < 64)
wake_up_bit(&ei->i_state_flags,
- EXT4_STATE_FC_COMMITTING);
+ EXT4_STATE_FC_COMMITTING);
#else
wake_up_bit(&ei->i_flags,
- EXT4_STATE_FC_COMMITTING);
+ EXT4_STATE_FC_COMMITTING);
#endif
}
list_del_init(&fc_dentry->fcd_dilist);
@@ -2548,13 +2646,20 @@ int __init ext4_fc_init_dentry_cache(void)
ext4_fc_dentry_cachep = KMEM_CACHE(ext4_fc_dentry_update,
SLAB_RECLAIM_ACCOUNT);
- if (ext4_fc_dentry_cachep == NULL)
+ if (!ext4_fc_dentry_cachep)
return -ENOMEM;
+ ext4_fc_range_cachep = KMEM_CACHE(ext4_fc_range, SLAB_RECLAIM_ACCOUNT);
+ if (!ext4_fc_range_cachep) {
+ kmem_cache_destroy(ext4_fc_dentry_cachep);
+ return -ENOMEM;
+ }
+
return 0;
}
void ext4_fc_destroy_dentry_cache(void)
{
+ kmem_cache_destroy(ext4_fc_range_cachep);
kmem_cache_destroy(ext4_fc_dentry_cachep);
}
--
2.53.0
^ permalink raw reply related
* [RFC v7 6/7] ext4: fast commit: add lock_updates tracepoint
From: Li Chen @ 2026-05-11 8:43 UTC (permalink / raw)
To: Zhang Yi, Theodore Ts'o, Andreas Dilger, Baokun Li, Jan Kara,
Ojaswin Mujoo, Ritesh Harjani (IBM), Zhang Yi, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, linux-ext4, linux-kernel,
linux-trace-kernel
In-Reply-To: <20260511084304.1559557-1-me@linux.beauty>
Commit-time fast commit snapshots run under jbd2_journal_lock_updates(),
so it is useful to quantify the time spent with updates locked and to
understand why snapshotting can fail.
Add a new tracepoint, ext4_fc_lock_updates, reporting the time spent in
the updates-locked window along with the number of snapshotted inodes
and ranges. Record the first snapshot failure reason in a stable snap_err
field for tooling.
Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes in v7:
- Address Sashiko review by reporting successfully snapshotted inode counts
in ext4_fc_lock_updates when snapshotting stops early.
Changes in v6:
- Drop explicit ext4_fc_snap_err assignments and rely on enum
auto-increment.
- Treat locked_ns as trace-only in this patch and calculate it only when
ext4_fc_lock_updates is enabled, as suggested by Steven Rostedt.
fs/ext4/ext4.h | 15 ++++++++
fs/ext4/fast_commit.c | 74 +++++++++++++++++++++++++++++--------
include/trace/events/ext4.h | 61 ++++++++++++++++++++++++++++++
3 files changed, 135 insertions(+), 15 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 2a706acdfaf8..df30f8705c98 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1027,6 +1027,21 @@ enum {
struct ext4_fc_inode_snap;
+/*
+ * Snapshot failure reasons for ext4_fc_lock_updates tracepoint.
+ * Keep these stable for tooling.
+ */
+enum ext4_fc_snap_err {
+ EXT4_FC_SNAP_ERR_NONE = 0,
+ EXT4_FC_SNAP_ERR_ES_MISS,
+ EXT4_FC_SNAP_ERR_ES_DELAYED,
+ EXT4_FC_SNAP_ERR_ES_OTHER,
+ EXT4_FC_SNAP_ERR_INODES_CAP,
+ EXT4_FC_SNAP_ERR_RANGES_CAP,
+ EXT4_FC_SNAP_ERR_NOMEM,
+ EXT4_FC_SNAP_ERR_INODE_LOC,
+};
+
/*
* fourth extended file system inode data in memory
*/
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 9fc17c1fa7af..c24984d8df83 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -194,6 +194,12 @@ static struct kmem_cache *ext4_fc_range_cachep;
#define EXT4_FC_SNAPSHOT_MAX_INODES 1024
#define EXT4_FC_SNAPSHOT_MAX_RANGES 2048
+static inline void ext4_fc_set_snap_err(int *snap_err, int err)
+{
+ if (snap_err && *snap_err == EXT4_FC_SNAP_ERR_NONE)
+ *snap_err = err;
+}
+
static void ext4_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
{
BUFFER_TRACE(bh, "");
@@ -967,11 +973,12 @@ static void ext4_fc_free_inode_snap(struct inode *inode)
static int ext4_fc_snapshot_inode_data(struct inode *inode,
struct list_head *ranges,
unsigned int nr_ranges_total,
- unsigned int *nr_rangesp)
+ unsigned int *nr_rangesp,
+ int *snap_err)
{
struct ext4_inode_info *ei = EXT4_I(inode);
- unsigned int nr_ranges = 0;
ext4_lblk_t start_lblk, end_lblk, cur_lblk;
+ unsigned int nr_ranges = 0;
spin_lock(&ei->i_fc_lock);
if (ei->i_fc_lblk_len == 0) {
@@ -996,11 +1003,16 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
ext4_lblk_t len;
u64 remaining = (u64)end_lblk - cur_lblk + 1;
- if (!ext4_es_lookup_extent(inode, cur_lblk, NULL, &es, NULL))
+ if (!ext4_es_lookup_extent(inode, cur_lblk, NULL, &es, NULL)) {
+ ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_MISS);
return -EAGAIN;
+ }
- if (ext4_es_is_delayed(&es))
+ if (ext4_es_is_delayed(&es)) {
+ ext4_fc_set_snap_err(snap_err,
+ EXT4_FC_SNAP_ERR_ES_DELAYED);
return -EAGAIN;
+ }
len = es.es_len - (cur_lblk - es.es_lblk);
if (len > remaining)
@@ -1010,12 +1022,17 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
continue;
}
- if (nr_ranges_total + nr_ranges >= EXT4_FC_SNAPSHOT_MAX_RANGES)
+ if (nr_ranges_total + nr_ranges >= EXT4_FC_SNAPSHOT_MAX_RANGES) {
+ ext4_fc_set_snap_err(snap_err,
+ EXT4_FC_SNAP_ERR_RANGES_CAP);
return -E2BIG;
+ }
range = kmem_cache_alloc(ext4_fc_range_cachep, GFP_NOFS);
- if (!range)
+ if (!range) {
+ ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_NOMEM);
return -ENOMEM;
+ }
nr_ranges++;
range->lblk = cur_lblk;
@@ -1040,6 +1057,7 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
range->len = max;
} else {
kmem_cache_free(ext4_fc_range_cachep, range);
+ ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_OTHER);
return -EAGAIN;
}
@@ -1059,7 +1077,7 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
static int ext4_fc_snapshot_inode(struct inode *inode,
unsigned int nr_ranges_total,
- unsigned int *nr_rangesp)
+ unsigned int *nr_rangesp, int *snap_err)
{
struct ext4_inode_info *ei = EXT4_I(inode);
struct ext4_fc_inode_snap *snap;
@@ -1071,8 +1089,10 @@ static int ext4_fc_snapshot_inode(struct inode *inode,
int alloc_ctx;
ret = ext4_get_inode_loc_noio(inode, &iloc);
- if (ret)
+ if (ret) {
+ ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_INODE_LOC);
return ret;
+ }
if (ext4_test_inode_flag(inode, EXT4_INODE_INLINE_DATA))
inode_len = EXT4_INODE_SIZE(inode->i_sb);
@@ -1081,6 +1101,7 @@ static int ext4_fc_snapshot_inode(struct inode *inode,
snap = kmalloc(struct_size(snap, inode_buf, inode_len), GFP_NOFS);
if (!snap) {
+ ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_NOMEM);
brelse(iloc.bh);
return -ENOMEM;
}
@@ -1091,7 +1112,7 @@ static int ext4_fc_snapshot_inode(struct inode *inode,
brelse(iloc.bh);
ret = ext4_fc_snapshot_inode_data(inode, &ranges, nr_ranges_total,
- &nr_ranges);
+ &nr_ranges, snap_err);
if (ret) {
kfree(snap);
ext4_fc_free_ranges(&ranges);
@@ -1192,7 +1213,10 @@ static int ext4_fc_alloc_snapshot_inodes(struct super_block *sb,
unsigned int *nr_inodesp);
static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes,
- unsigned int inodes_size)
+ unsigned int inodes_size,
+ unsigned int *nr_inodesp,
+ unsigned int *nr_rangesp,
+ int *snap_err)
{
struct super_block *sb = journal->j_private;
struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -1210,6 +1234,8 @@ static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes,
alloc_ctx = ext4_fc_lock(sb);
list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
if (i >= inodes_size) {
+ ext4_fc_set_snap_err(snap_err,
+ EXT4_FC_SNAP_ERR_INODES_CAP);
ret = -E2BIG;
goto unlock;
}
@@ -1233,6 +1259,8 @@ static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes,
continue;
if (i >= inodes_size) {
+ ext4_fc_set_snap_err(snap_err,
+ EXT4_FC_SNAP_ERR_INODES_CAP);
ret = -E2BIG;
goto unlock;
}
@@ -1257,16 +1285,20 @@ static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes,
unsigned int inode_ranges = 0;
ret = ext4_fc_snapshot_inode(inodes[idx], nr_ranges,
- &inode_ranges);
+ &inode_ranges, snap_err);
if (ret)
break;
nr_ranges += inode_ranges;
}
+ if (nr_inodesp)
+ *nr_inodesp = idx;
+ if (nr_rangesp)
+ *nr_rangesp = nr_ranges;
return ret;
}
-static int ext4_fc_perform_commit(journal_t *journal)
+static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid)
{
struct super_block *sb = journal->j_private;
struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -1275,10 +1307,15 @@ static int ext4_fc_perform_commit(journal_t *journal)
struct inode *inode;
struct inode **inodes;
unsigned int inodes_size;
+ unsigned int snap_inodes = 0;
+ unsigned int snap_ranges = 0;
+ int snap_err = EXT4_FC_SNAP_ERR_NONE;
struct blk_plug plug;
int ret = 0;
u32 crc = 0;
int alloc_ctx;
+ ktime_t lock_start;
+ u64 locked_ns;
/*
* Step 1: Mark all inodes on s_fc_q[MAIN] with
@@ -1326,13 +1363,13 @@ static int ext4_fc_perform_commit(journal_t *journal)
if (ret)
return ret;
-
ret = ext4_fc_alloc_snapshot_inodes(sb, &inodes, &inodes_size);
if (ret)
return ret;
/* Step 4: Mark all inodes as being committed. */
jbd2_journal_lock_updates(journal);
+ lock_start = ktime_get();
/*
* The journal is now locked. No more handles can start and all the
* previous handles are now drained. Snapshotting happens in this
@@ -1346,8 +1383,15 @@ static int ext4_fc_perform_commit(journal_t *journal)
}
ext4_fc_unlock(sb, alloc_ctx);
- ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size);
+ ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size,
+ &snap_inodes, &snap_ranges, &snap_err);
jbd2_journal_unlock_updates(journal);
+ if (trace_ext4_fc_lock_updates_enabled()) {
+ locked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start));
+ trace_ext4_fc_lock_updates(sb, commit_tid, locked_ns,
+ snap_inodes, snap_ranges, ret,
+ snap_err);
+ }
kvfree(inodes);
if (ret)
return ret;
@@ -1552,7 +1596,7 @@ int ext4_fc_commit(journal_t *journal, tid_t commit_tid)
journal_ioprio = EXT4_DEF_JOURNAL_IOPRIO;
set_task_ioprio(current, journal_ioprio);
fc_bufs_before = (sbi->s_fc_bytes + bsize - 1) / bsize;
- ret = ext4_fc_perform_commit(journal);
+ ret = ext4_fc_perform_commit(journal, commit_tid);
if (ret < 0) {
if (ret == -EAGAIN || ret == -E2BIG || ret == -ECANCELED)
status = EXT4_FC_STATUS_INELIGIBLE;
diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index f493642cf121..7028a28316fa 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -107,6 +107,26 @@ TRACE_DEFINE_ENUM(EXT4_FC_REASON_VERITY);
TRACE_DEFINE_ENUM(EXT4_FC_REASON_MOVE_EXT);
TRACE_DEFINE_ENUM(EXT4_FC_REASON_MAX);
+#undef EM
+#undef EMe
+#define EM(a) TRACE_DEFINE_ENUM(EXT4_FC_SNAP_ERR_##a);
+#define EMe(a) TRACE_DEFINE_ENUM(EXT4_FC_SNAP_ERR_##a);
+
+#define TRACE_SNAP_ERR \
+ EM(NONE) \
+ EM(ES_MISS) \
+ EM(ES_DELAYED) \
+ EM(ES_OTHER) \
+ EM(INODES_CAP) \
+ EM(RANGES_CAP) \
+ EM(NOMEM) \
+ EMe(INODE_LOC)
+
+TRACE_SNAP_ERR
+
+#undef EM
+#undef EMe
+
#define show_fc_reason(reason) \
__print_symbolic(reason, \
{ EXT4_FC_REASON_XATTR, "XATTR"}, \
@@ -2818,6 +2838,47 @@ TRACE_EVENT(ext4_fc_commit_stop,
__entry->num_fc_ineligible, __entry->nblks_agg, __entry->tid)
);
+#define EM(a) { EXT4_FC_SNAP_ERR_##a, #a },
+#define EMe(a) { EXT4_FC_SNAP_ERR_##a, #a }
+
+TRACE_EVENT(ext4_fc_lock_updates,
+ TP_PROTO(struct super_block *sb, tid_t commit_tid, u64 locked_ns,
+ unsigned int nr_inodes, unsigned int nr_ranges, int err,
+ int snap_err),
+
+ TP_ARGS(sb, commit_tid, locked_ns, nr_inodes, nr_ranges, err, snap_err),
+
+ TP_STRUCT__entry(/* entry */
+ __field(dev_t, dev)
+ __field(tid_t, tid)
+ __field(u64, locked_ns)
+ __field(unsigned int, nr_inodes)
+ __field(unsigned int, nr_ranges)
+ __field(int, err)
+ __field(int, snap_err)
+ ),
+
+ TP_fast_assign(/* assign */
+ __entry->dev = sb->s_dev;
+ __entry->tid = commit_tid;
+ __entry->locked_ns = locked_ns;
+ __entry->nr_inodes = nr_inodes;
+ __entry->nr_ranges = nr_ranges;
+ __entry->err = err;
+ __entry->snap_err = snap_err;
+ ),
+
+ TP_printk("dev %d,%d tid %u locked_ns %llu nr_inodes %u nr_ranges %u err %d snap_err %s",
+ MAJOR(__entry->dev), MINOR(__entry->dev), __entry->tid,
+ __entry->locked_ns, __entry->nr_inodes, __entry->nr_ranges,
+ __entry->err, __print_symbolic(__entry->snap_err,
+ TRACE_SNAP_ERR))
+);
+
+#undef EM
+#undef EMe
+#undef TRACE_SNAP_ERR
+
#define FC_REASON_NAME_STAT(reason) \
show_fc_reason(reason), \
__entry->fc_ineligible_rc[reason]
--
2.53.0
^ permalink raw reply related
* [RFC v7 7/7] ext4: fast commit: export snapshot stats in fc_info
From: Li Chen @ 2026-05-11 8:43 UTC (permalink / raw)
To: Zhang Yi, Theodore Ts'o, Andreas Dilger, Baokun Li, Jan Kara,
Ojaswin Mujoo, Ritesh Harjani (IBM), Zhang Yi, linux-ext4,
linux-kernel
Cc: Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel
In-Reply-To: <20260511084304.1559557-1-me@linux.beauty>
Snapshot-based fast commit can fall back when the commit-time snapshot
cannot be built (e.g. extent status cache misses). It is useful to
quantify the updates-locked window and to see why snapshotting failed.
Add best-effort snapshot counters to the ext4 superblock and extend
/proc/fs/ext4/<sb_id>/fc_info to report the number of snapshotted
inodes and ranges, snapshot failure reasons, and the average/max time
spent with journal updates locked.
Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
Changes in v7:
- Address Sashiko review by using READ_ONCE() + div64_u64() for the fc_info
lock_updates average.
Changes in v6:
- Start consuming locked_ns in fc_info, so this patch intentionally moves
lock_updates_ns_{total,max,samples} accounting here.
- Guard the tracepoint call with trace_ext4_fc_lock_updates_enabled() and
use trace_call__ext4_fc_lock_updates() to avoid the double static_branch
at the guarded call site.
- Keep the stats unconditionally while avoiding extra tracepoint
overhead when ext4_fc_lock_updates is disabled.
fs/ext4/ext4.h | 31 +++++++++++++++++
fs/ext4/fast_commit.c | 78 +++++++++++++++++++++++++++++++++++++------
fs/ext4/super.c | 1 +
3 files changed, 100 insertions(+), 10 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index df30f8705c98..3457b4950c02 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1550,6 +1550,36 @@ struct ext4_orphan_info {
* file blocks */
};
+/*
+ * Ext4 fast commit snapshot statistics.
+ *
+ * These are best-effort counters intended for debugging / performance
+ * introspection; they are not exact under concurrent updates.
+ */
+struct ext4_fc_snap_stats {
+ u64 lock_updates_ns_total;
+ u64 lock_updates_ns_max;
+ u64 lock_updates_samples;
+
+ u64 snap_inodes;
+ u64 snap_ranges;
+
+ u64 snap_fail_es_miss;
+ u64 snap_fail_es_delayed;
+ u64 snap_fail_es_other;
+
+ u64 snap_fail_inodes_cap;
+ u64 snap_fail_ranges_cap;
+ u64 snap_fail_nomem;
+ u64 snap_fail_inode_loc;
+
+ /*
+ * Missing inode snapshots during log writing should never happen.
+ * Keep this counter to help catch unexpected regressions.
+ */
+ u64 snap_fail_no_snap;
+};
+
/*
* fourth extended-fs super-block data in memory
*/
@@ -1824,6 +1854,7 @@ struct ext4_sb_info {
struct mutex s_fc_lock;
struct buffer_head *s_fc_bh;
struct ext4_fc_stats s_fc_stats;
+ struct ext4_fc_snap_stats s_fc_snap_stats;
tid_t s_fc_ineligible_tid;
#ifdef CONFIG_EXT4_DEBUG
int s_fc_debug_max_replay;
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index c24984d8df83..1dfcccf4179e 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -874,13 +874,17 @@ static int ext4_fc_write_inode(struct inode *inode, u32 *crc)
int inode_len;
int ret;
- if (!snap)
+ if (!snap) {
+ EXT4_SB(inode->i_sb)->s_fc_snap_stats.snap_fail_no_snap++;
return -ECANCELED;
+ }
src = snap->inode_buf;
inode_len = snap->inode_len;
- if (!src || inode_len == 0)
+ if (!src || inode_len == 0) {
+ EXT4_SB(inode->i_sb)->s_fc_snap_stats.snap_fail_no_snap++;
return -ECANCELED;
+ }
fc_inode.fc_ino = cpu_to_le32(inode->i_ino);
tl.fc_tag = cpu_to_le16(EXT4_FC_TAG_INODE);
@@ -915,8 +919,10 @@ static int ext4_fc_write_inode_data(struct inode *inode, u32 *crc)
struct ext4_extent *ex;
struct ext4_fc_range *range;
- if (!snap)
+ if (!snap) {
+ EXT4_SB(inode->i_sb)->s_fc_snap_stats.snap_fail_no_snap++;
return -ECANCELED;
+ }
list_for_each_entry(range, &snap->data_list, list) {
if (range->tag == EXT4_FC_TAG_DEL_RANGE) {
@@ -977,6 +983,8 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
int *snap_err)
{
struct ext4_inode_info *ei = EXT4_I(inode);
+ struct ext4_fc_snap_stats *stats =
+ &EXT4_SB(inode->i_sb)->s_fc_snap_stats;
ext4_lblk_t start_lblk, end_lblk, cur_lblk;
unsigned int nr_ranges = 0;
@@ -1004,11 +1012,13 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
u64 remaining = (u64)end_lblk - cur_lblk + 1;
if (!ext4_es_lookup_extent(inode, cur_lblk, NULL, &es, NULL)) {
+ stats->snap_fail_es_miss++;
ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_MISS);
return -EAGAIN;
}
if (ext4_es_is_delayed(&es)) {
+ stats->snap_fail_es_delayed++;
ext4_fc_set_snap_err(snap_err,
EXT4_FC_SNAP_ERR_ES_DELAYED);
return -EAGAIN;
@@ -1023,6 +1033,7 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
}
if (nr_ranges_total + nr_ranges >= EXT4_FC_SNAPSHOT_MAX_RANGES) {
+ stats->snap_fail_ranges_cap++;
ext4_fc_set_snap_err(snap_err,
EXT4_FC_SNAP_ERR_RANGES_CAP);
return -E2BIG;
@@ -1030,6 +1041,7 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
range = kmem_cache_alloc(ext4_fc_range_cachep, GFP_NOFS);
if (!range) {
+ stats->snap_fail_nomem++;
ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_NOMEM);
return -ENOMEM;
}
@@ -1057,6 +1069,7 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode,
range->len = max;
} else {
kmem_cache_free(ext4_fc_range_cachep, range);
+ stats->snap_fail_es_other++;
ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_OTHER);
return -EAGAIN;
}
@@ -1080,6 +1093,8 @@ static int ext4_fc_snapshot_inode(struct inode *inode,
unsigned int *nr_rangesp, int *snap_err)
{
struct ext4_inode_info *ei = EXT4_I(inode);
+ struct ext4_fc_snap_stats *stats =
+ &EXT4_SB(inode->i_sb)->s_fc_snap_stats;
struct ext4_fc_inode_snap *snap;
int inode_len = EXT4_GOOD_OLD_INODE_SIZE;
struct ext4_iloc iloc;
@@ -1090,6 +1105,7 @@ static int ext4_fc_snapshot_inode(struct inode *inode,
ret = ext4_get_inode_loc_noio(inode, &iloc);
if (ret) {
+ stats->snap_fail_inode_loc++;
ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_INODE_LOC);
return ret;
}
@@ -1101,6 +1117,7 @@ static int ext4_fc_snapshot_inode(struct inode *inode,
snap = kmalloc(struct_size(snap, inode_buf, inode_len), GFP_NOFS);
if (!snap) {
+ stats->snap_fail_nomem++;
ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_NOMEM);
brelse(iloc.bh);
return -ENOMEM;
@@ -1125,6 +1142,8 @@ static int ext4_fc_snapshot_inode(struct inode *inode,
list_splice_tail_init(&ranges, &snap->data_list);
ext4_fc_unlock(inode->i_sb, alloc_ctx);
+ stats->snap_inodes++;
+ stats->snap_ranges += nr_ranges;
if (nr_rangesp)
*nr_rangesp = nr_ranges;
return 0;
@@ -1234,6 +1253,7 @@ static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes,
alloc_ctx = ext4_fc_lock(sb);
list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
if (i >= inodes_size) {
+ sbi->s_fc_snap_stats.snap_fail_inodes_cap++;
ext4_fc_set_snap_err(snap_err,
EXT4_FC_SNAP_ERR_INODES_CAP);
ret = -E2BIG;
@@ -1259,6 +1279,7 @@ static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes,
continue;
if (i >= inodes_size) {
+ sbi->s_fc_snap_stats.snap_fail_inodes_cap++;
ext4_fc_set_snap_err(snap_err,
EXT4_FC_SNAP_ERR_INODES_CAP);
ret = -E2BIG;
@@ -1302,6 +1323,7 @@ static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid)
{
struct super_block *sb = journal->j_private;
struct ext4_sb_info *sbi = EXT4_SB(sb);
+ struct ext4_fc_snap_stats *snap_stats = &sbi->s_fc_snap_stats;
struct ext4_inode_info *iter;
struct ext4_fc_head head;
struct inode *inode;
@@ -1364,8 +1386,13 @@ static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid)
return ret;
ret = ext4_fc_alloc_snapshot_inodes(sb, &inodes, &inodes_size);
- if (ret)
+ if (ret) {
+ if (ret == -E2BIG)
+ snap_stats->snap_fail_inodes_cap++;
+ else if (ret == -ENOMEM)
+ snap_stats->snap_fail_nomem++;
return ret;
+ }
/* Step 4: Mark all inodes as being committed. */
jbd2_journal_lock_updates(journal);
@@ -1386,12 +1413,15 @@ static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid)
ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size,
&snap_inodes, &snap_ranges, &snap_err);
jbd2_journal_unlock_updates(journal);
- if (trace_ext4_fc_lock_updates_enabled()) {
- locked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start));
- trace_ext4_fc_lock_updates(sb, commit_tid, locked_ns,
- snap_inodes, snap_ranges, ret,
- snap_err);
- }
+ locked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start));
+ snap_stats->lock_updates_ns_total += locked_ns;
+ snap_stats->lock_updates_samples++;
+ if (locked_ns > snap_stats->lock_updates_ns_max)
+ snap_stats->lock_updates_ns_max = locked_ns;
+ if (trace_ext4_fc_lock_updates_enabled())
+ trace_call__ext4_fc_lock_updates(sb, commit_tid, locked_ns,
+ snap_inodes, snap_ranges,
+ ret, snap_err);
kvfree(inodes);
if (ret)
return ret;
@@ -2667,11 +2697,23 @@ int ext4_fc_info_show(struct seq_file *seq, void *v)
{
struct ext4_sb_info *sbi = EXT4_SB((struct super_block *)seq->private);
struct ext4_fc_stats *stats = &sbi->s_fc_stats;
+ struct ext4_fc_snap_stats *snap_stats = &sbi->s_fc_snap_stats;
+ u64 lock_avg_ns = 0;
+ u64 lock_updates_samples;
+ u64 lock_updates_ns_total;
+ u64 lock_updates_ns_max;
int i;
if (v != SEQ_START_TOKEN)
return 0;
+ lock_updates_samples = READ_ONCE(snap_stats->lock_updates_samples);
+ lock_updates_ns_total = READ_ONCE(snap_stats->lock_updates_ns_total);
+ lock_updates_ns_max = READ_ONCE(snap_stats->lock_updates_ns_max);
+ if (lock_updates_samples)
+ lock_avg_ns = div64_u64(lock_updates_ns_total,
+ lock_updates_samples);
+
seq_printf(seq,
"fc stats:\n%ld commits\n%ld ineligible\n%ld numblks\n%lluus avg_commit_time\n",
stats->fc_num_commits, stats->fc_ineligible_commits,
@@ -2682,6 +2724,22 @@ int ext4_fc_info_show(struct seq_file *seq, void *v)
seq_printf(seq, "\"%s\":\t%d\n", fc_ineligible_reasons[i],
stats->fc_ineligible_reason_count[i]);
+ seq_printf(seq,
+ "Snapshot stats:\n%llu inodes\n%llu ranges\n%lluus lock_updates_avg\n%lluus lock_updates_max\n",
+ snap_stats->snap_inodes, snap_stats->snap_ranges,
+ div_u64(lock_avg_ns, 1000),
+ div_u64(lock_updates_ns_max, 1000));
+ seq_printf(seq,
+ "Snapshot failures:\n%llu es_miss\n%llu es_delayed\n%llu es_other\n%llu inodes_cap\n%llu ranges_cap\n%llu nomem\n%llu inode_loc\n%llu no_snap\n",
+ snap_stats->snap_fail_es_miss,
+ snap_stats->snap_fail_es_delayed,
+ snap_stats->snap_fail_es_other,
+ snap_stats->snap_fail_inodes_cap,
+ snap_stats->snap_fail_ranges_cap,
+ snap_stats->snap_fail_nomem,
+ snap_stats->snap_fail_inode_loc,
+ snap_stats->snap_fail_no_snap);
+
return 0;
}
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 3c869f0001c5..f1f8819a2a23 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4544,6 +4544,7 @@ static void ext4_fast_commit_init(struct super_block *sb)
sbi->s_fc_ineligible_tid = 0;
mutex_init(&sbi->s_fc_lock);
memset(&sbi->s_fc_stats, 0, sizeof(sbi->s_fc_stats));
+ memset(&sbi->s_fc_snap_stats, 0, sizeof(sbi->s_fc_snap_stats));
sbi->s_fc_replay_state.fc_regions = NULL;
sbi->s_fc_replay_state.fc_regions_size = 0;
sbi->s_fc_replay_state.fc_regions_used = 0;
--
2.53.0
^ permalink raw reply related
* [PATCH] tracing/probes: Ensure the uprobe buffer size is bigger than event size
From: Masami Hiramatsu (Google) @ 2026-05-11 10:03 UTC (permalink / raw)
To: Steven Rostedt, Masami Hiramatsu
Cc: Mathieu Desnoyers, linux-kernel, linux-trace-kernel
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Add BUILD_BUG_ON() to ensure the uprobe per-CPU working buffer
size is bigger than the event size.
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
kernel/trace/trace_uprobe.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 2cabf8a23ec5..c5ee7920dec6 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -979,6 +979,7 @@ static struct uprobe_cpu_buffer *prepare_uprobe_buffer(struct trace_uprobe *tu,
ucb = uprobe_buffer_get();
ucb->dsize = tu->tp.size + dsize;
+ BUILD_BUG_ON(MAX_UCB_BUFFER_SIZE < MAX_PROBE_EVENT_SIZE);
if (WARN_ON_ONCE(ucb->dsize > MAX_UCB_BUFFER_SIZE)) {
ucb->dsize = MAX_UCB_BUFFER_SIZE;
dsize = MAX_UCB_BUFFER_SIZE - tu->tp.size;
^ permalink raw reply related
* Re: [PATCH 07/13] rv: Simply hybrid automata monitors's clock variables
From: Nam Cao @ 2026-05-11 11:55 UTC (permalink / raw)
To: Gabriele Monaco
Cc: Steven Rostedt, Wander Lairson Costa, linux-trace-kernel,
linux-kernel
In-Reply-To: <967f1cd8cd6e27aaa65d68194487306bc312caa0.camel@redhat.com>
Gabriele Monaco <gmonaco@redhat.com> writes:
> Well, this is roughly what we discussed in [1].
> Now, I didn't submit the throttle monitor yet because it depends on unacked
> tracepoints.
Thanks for bringing that up. I had no memory of that discussion.
> In short, this works with the assumption that the expires value you pass to
> ha_check_invariant() is the same you used to arm the timer.
>
> That's true for constant values only (the deadline) but not for something like
> the runtime. I couldn't think of a way to rearrange that model not to require
> the runtime left field.
I believe you are referring to this:
|
|
dl_replenish;reset(clk) v
sched_switch_in #=========================# sched_switch_in;
+--------------- H H reset(clk)
| H H <----------------+
+--------------> H running H |
dl_throttle;reset(clk) H clk < runtime_left_ns() H |
+--------------------------- H H sched_switch_out |
| +------------------> H H -------------+ |
| dl_replenish;reset(clk) #=========================# | |
| | | ^ | |
v | dl_defer_arm | | |
Now that I stared at this again, I think we already deviate from theory
here. Our documentation mentions that the invariant must be in the form
g = v < c | true
with "c [being] a numerical value".
The invariant "clk < runtime_left_ns()" means clk must not exceed the
remaining runtime, which is sampled by calling runtime_left_ns() when
the state is entered. This is not in the theory. Additionally, I think
this interpretation is ambiguous; one could also interpret that as "the
clk value must never exceed the *current* value returned by
runtime_left_ns()".
I digged into the cited academic papers, but couldn't find anything that
can describe this. The closest I see is the "init" label for states, but
that is the condition for entering the states.
> Otherwise.. We could read the remaining time in the timer, but we wouldn't be
> able to simulate ns precision when using the timer wheel.
>
> Now if we really wanted to go down that path, we are using a union to allocate
> either timer or hrtimer, the latter is larger, so we /could/ add a u64 expire_ns
> field to the ha_monitor struct without needing additional memory.
>
> If that doesn't sound too wild to you, I may try and sketch something up to see
> if that's viable. Then this patch could go through as is and I would add the
> extension together with the submission of throttle.
That can work, but not ideal, because hrtimer will not be usable.
Looking at the throttle monitor again, is it possible to rewrite
runtime_left_ns() to read .dl_runtime instead of .runtime? I don't know
the deadline schedule very well, but I think .dl_runtime is not changing
like .runtime?
Nam
^ permalink raw reply
* Re: [PATCH bpf 1/2] uprobes/x86: Fix red zone clobbering in nop5 optimization
From: Oleg Nesterov @ 2026-05-11 14:45 UTC (permalink / raw)
To: Andrii Nakryiko; +Cc: bpf, linux-trace-kernel, jolsa, peterz, mingo, mhiramat
In-Reply-To: <20260509003146.976844-1-andrii@kernel.org>
On 05/08, Andrii Nakryiko wrote:
>
> +static bool resolve_uprobe_addr(unsigned long ip, unsigned long *probe_addr)
> {
> - struct vm_area_struct *vma = vma_lookup(current->mm, ip);
> + struct uprobes_state *state = ¤t->mm->uprobes_state;
it seems that there is a problem, with or without this change...
Lets forget about this patch for the moment, I am still trying to understand it.
What if register_for_each_vma() calls install_breakpoint(vma) and
vma->mm != current->mm ?
In this case install_breakpoint() path will call __is_optimized() and then
__in_uprobe_trampoline() which does vma_lookup(current->mm). This looks
obviously wrong ?
And unless I am totally confused, this patch "inherits" the problem...
No?
Oleg.
^ permalink raw reply
* [PATCH v6 0/4] mm/memory-failure: add panic option for unrecoverable pages
From: Breno Leitao @ 2026-05-11 15:38 UTC (permalink / raw)
To: Miaohe Lin, Naoya Horiguchi, Andrew Morton, Jonathan Corbet,
Shuah Khan, David Hildenbrand, Lorenzo Stoakes, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan,
Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
Liam R. Howlett
Cc: linux-mm, linux-kernel, linux-doc, linux-kselftest, Breno Leitao,
linux-trace-kernel, kernel-team, Lance Yang
Changes from previouis version
* Replaced the late, action-time recheck for MF_MSG_KERNEL_HIGH_ORDER
with early failure classification inside get_any_page() (new patch
2/4).
* David Hildenbrand pointed out that the recheck inspected refcount and
folio mapping without holding a folio reference, which is unsafe
(concurrent split can trigger VM_WARN_ON_FOLIO).
* Lance Yang suggested moving the disambiguation to the call site that
still knows *why* the page reference could not be taken, which is what
this version does via a new enum mf_get_page_status (MF_GET_PAGE_OK
/ RACE / UNHANDLABLE) plumbed out through get_hwpoison_page().
Signed-off-by: Breno Leitao <leitao@debian.org>
---
Changes in v6:
- Dropped the selftest given the value was not clear
- Get the status of the failure from get_any_page()
- Small nits from different people/AIs.
- Link to v5: https://patch.msgid.link/20260424-ecc_panic-v5-0-a35f4b50425c@debian.org
Changes in v5:
- Add vm.panic_on_unrecoverable_memory_failure sysctl to panic on
unrecoverable kernel page hwpoison events (reserved pages, refcount-0
non-buddy pages, unknown state), with a recheck to avoid racing with
concurrent buddy allocations. (Miaohe)
- Distinguish reserved pages as MF_MSG_KERNEL in memory_failure(),
document the new sysctl in Documentation/admin-guide/sysctl/vm.rst,
and add a selftest verifying SIGBUS recovery on userspace pages still
works when the sysctl is enabled. (Miaohe)
- Added a selftest
- Link to v4:
https://patch.msgid.link/20260415-ecc_panic-v4-0-2d0277f8f601@debian.org
Changes in v4:
- Drop CONFIG_BOOTPARAM_MEMORY_FAILURE_PANIC kernel configuration option.
- Split the reserved page classification (MF_MSG_KERNEL) into its own
patch, separate from the panic mechanism.
- Document why the buddy allocator TOCTOU race (between
get_hwpoison_page() and is_free_buddy_page()) cannot cause false
positives: PG_hwpoison is set beforehand and check_new_page() in the
page allocator rejects hwpoisoned pages.
- Document the narrow LRU isolation race window for MF_MSG_UNKNOWN and
its mitigation via identify_page_state()'s two-pass design.
- Explicitly document why MF_MSG_GET_HWPOISON is excluded from the
panic conditions (shared path with transient races and non-reserved
kernel memory).
- Link to v3: https://patch.msgid.link/20260413-ecc_panic-v3-0-1dcbb2f12bc4@debian.org
Changes in v3:
- Rename is_unrecoverable_memory_failure() to panic_on_unrecoverable_mf()
as suggested by maintainer.
- Add CONFIG_BOOTPARAM_MEMORY_FAILURE_PANIC kernel configuration option,
similar to CONFIG_BOOTPARAM_HARDLOCKUP_PANIC.
- Add documentation for the sysctl and CONFIG option.
- Add code comments documenting the panic condition design rationale and
how the retry mechanism mitigates false positives from buddy allocator
races.
- Link to v2: https://patch.msgid.link/20260331-ecc_panic-v2-0-9e40d0f64f7a@debian.org
Changes in v2:
- Panic on MF_MSG_KERNEL, MF_MSG_KERNEL_HIGH_ORDER and MF_MSG_UNKNOWN
instead of MF_MSG_GET_HWPOISON.
- Report MF_MSG_KERNEL for reserved pages when get_hwpoison_page() fails
instead of MF_MSG_GET_HWPOISON.
- Link to v1: https://patch.msgid.link/20260323-ecc_panic-v1-0-72a1921726c5@debian.org
To: Miaohe Lin <linmiaohe@huawei.com>
To: Naoya Horiguchi <nao.horiguchi@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Jonathan Corbet <corbet@lwn.net>
To: Shuah Khan <skhan@linuxfoundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-trace-kernel@vger.kernel.org
Cc: linux-doc@vger.kernel.org
---
Breno Leitao (4):
mm/memory-failure: report MF_MSG_KERNEL for reserved pages
mm/memory-failure: classify get_any_page() failures by reason
mm/memory-failure: add panic option for unrecoverable pages
Documentation: document panic_on_unrecoverable_memory_failure sysctl
Documentation/admin-guide/sysctl/vm.rst | 70 ++++++++++++++++++++++++++
include/trace/events/memory-failure.h | 2 +-
mm/memory-failure.c | 89 ++++++++++++++++++++++++++++++---
3 files changed, 152 insertions(+), 9 deletions(-)
---
base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
change-id: 20260323-ecc_panic-4e473b83087c
Best regards,
--
Breno Leitao <leitao@debian.org>
^ permalink raw reply
* [PATCH v6 1/4] mm/memory-failure: report MF_MSG_KERNEL for reserved pages
From: Breno Leitao @ 2026-05-11 15:38 UTC (permalink / raw)
To: Miaohe Lin, Naoya Horiguchi, Andrew Morton, Jonathan Corbet,
Shuah Khan, David Hildenbrand, Lorenzo Stoakes, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan,
Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
Liam R. Howlett
Cc: linux-mm, linux-kernel, linux-doc, linux-kselftest, Breno Leitao,
linux-trace-kernel, kernel-team, Lance Yang
In-Reply-To: <20260511-ecc_panic-v6-0-183012ba7d4b@debian.org>
When get_hwpoison_page() returns a negative value, distinguish
reserved pages from other failure cases by reporting MF_MSG_KERNEL
instead of MF_MSG_GET_HWPOISON. Reserved pages belong to the kernel
and should be classified accordingly for proper handling.
Sample PG_reserved before the get_hwpoison_page() call. In the
MF_COUNT_INCREASED path get_any_page() can drop the caller's
reference before returning -EIO, after which the underlying page may
have been freed and reallocated with page->flags reset; reading
PageReserved(p) at that point would observe stale or unrelated state.
The pre-call snapshot reflects what the page actually was at the
time of the failure event.
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
mm/memory-failure.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 866c4428ac7ef..f112fb27a8ff6 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2348,6 +2348,7 @@ int memory_failure(unsigned long pfn, int flags)
unsigned long page_flags;
bool retry = true;
int hugetlb = 0;
+ bool is_reserved;
if (!sysctl_memory_failure_recovery)
panic("Memory failure on page %lx", pfn);
@@ -2411,6 +2412,18 @@ int memory_failure(unsigned long pfn, int flags)
* In fact it's dangerous to directly bump up page count from 0,
* that may make page_ref_freeze()/page_ref_unfreeze() mismatch.
*/
+ /*
+ * Pages with PG_reserved set are not currently managed by the
+ * page allocator (memblock-reserved memory, driver reservations,
+ * etc.), so classify them as kernel-owned for reporting.
+ *
+ * Sample the flag before get_hwpoison_page(): in the
+ * MF_COUNT_INCREASED path, get_any_page() can drop the caller's
+ * reference before returning -EIO, after which page->flags may
+ * have been reset by the allocator.
+ */
+ is_reserved = PageReserved(p);
+
res = get_hwpoison_page(p, flags);
if (!res) {
if (is_free_buddy_page(p)) {
@@ -2432,7 +2445,11 @@ int memory_failure(unsigned long pfn, int flags)
}
goto unlock_mutex;
} else if (res < 0) {
- res = action_result(pfn, MF_MSG_GET_HWPOISON, MF_IGNORED);
+ if (is_reserved)
+ res = action_result(pfn, MF_MSG_KERNEL, MF_IGNORED);
+ else
+ res = action_result(pfn, MF_MSG_GET_HWPOISON,
+ MF_IGNORED);
goto unlock_mutex;
}
--
2.53.0-Meta
^ permalink raw reply related
* [PATCH v6 2/4] mm/memory-failure: classify get_any_page() failures by reason
From: Breno Leitao @ 2026-05-11 15:38 UTC (permalink / raw)
To: Miaohe Lin, Naoya Horiguchi, Andrew Morton, Jonathan Corbet,
Shuah Khan, David Hildenbrand, Lorenzo Stoakes, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan,
Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
Liam R. Howlett
Cc: linux-mm, linux-kernel, linux-doc, linux-kselftest, Breno Leitao,
linux-trace-kernel, kernel-team, Lance Yang
In-Reply-To: <20260511-ecc_panic-v6-0-183012ba7d4b@debian.org>
When get_any_page() fails to grab a page reference, the *reason* it
failed is known at the call site but is not surfaced to callers: the
HWPoisonHandlable() rejection path (a stable kernel page hwpoison cannot
handle — slab, vmalloc, page tables, kernel stacks, ...) and the
page_count() / put_page race paths (a transient page-allocator lifecycle
race) all collapse to a single negative errno by the time
memory_failure() sees them. memory_failure() can only observe the
conflated result and reports both as MF_MSG_GET_HWPOISON.
Surface the diagnosis explicitly. Add an mf_get_page_status enum,
plumbed out through get_any_page() and get_hwpoison_page() (NULL is
accepted by callers that do not care — unpoison_memory() and
soft_offline_page() pass NULL). get_any_page() sets the status at the
moment it gives up:
MF_GET_PAGE_UNHANDLABLE — HWPoisonHandlable() rejected the page
after retries.
MF_GET_PAGE_RACE — exhausted retries on a refcount /
lifecycle race with the allocator.
memory_failure() then promotes the unhandlable case to MF_MSG_KERNEL
alongside the existing PageReserved branch, and leaves the
transient-race case as MF_MSG_GET_HWPOISON. This forms the foundation
a later patch will rely on to decide whether an unrecoverable failure
should panic.
Drop the "reserved" qualifier from action_page_types[MF_MSG_KERNEL]
and the matching tracepoint string in MF_PAGE_TYPE: the enum value
now covers both PageReserved pages and unhandlable kernel pages
(slab, vmalloc, page tables, kernel stacks, ...), so "kernel page"
is the accurate label for both populations.
Suggested-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
include/trace/events/memory-failure.h | 2 +-
mm/memory-failure.c | 46 +++++++++++++++++++++++++++++------
2 files changed, 39 insertions(+), 9 deletions(-)
diff --git a/include/trace/events/memory-failure.h b/include/trace/events/memory-failure.h
index aa57cc8f896be..8a860e6fcb4e9 100644
--- a/include/trace/events/memory-failure.h
+++ b/include/trace/events/memory-failure.h
@@ -24,7 +24,7 @@
EMe ( MF_RECOVERED, "Recovered" )
#define MF_PAGE_TYPE \
- EM ( MF_MSG_KERNEL, "reserved kernel page" ) \
+ EM ( MF_MSG_KERNEL, "kernel page" ) \
EM ( MF_MSG_KERNEL_HIGH_ORDER, "high-order kernel page" ) \
EM ( MF_MSG_HUGE, "huge page" ) \
EM ( MF_MSG_FREE_HUGE, "free huge page" ) \
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index f112fb27a8ff6..4210173060aac 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -878,7 +878,7 @@ static const char *action_name[] = {
};
static const char * const action_page_types[] = {
- [MF_MSG_KERNEL] = "reserved kernel page",
+ [MF_MSG_KERNEL] = "kernel page",
[MF_MSG_KERNEL_HIGH_ORDER] = "high-order kernel page",
[MF_MSG_HUGE] = "huge page",
[MF_MSG_FREE_HUGE] = "free huge page",
@@ -1389,11 +1389,29 @@ static int __get_hwpoison_page(struct page *page, unsigned long flags)
#define GET_PAGE_MAX_RETRY_NUM 3
-static int get_any_page(struct page *p, unsigned long flags)
+enum mf_get_page_status {
+ MF_GET_PAGE_OK = 0,
+ MF_GET_PAGE_RACE,
+ MF_GET_PAGE_UNHANDLABLE,
+};
+
+static void set_mf_get_page_status(enum mf_get_page_status *gp_status,
+ enum mf_get_page_status value)
+{
+ if (!gp_status)
+ return;
+
+ *gp_status = value;
+}
+
+static int get_any_page(struct page *p, unsigned long flags,
+ enum mf_get_page_status *gp_status)
{
int ret = 0, pass = 0;
bool count_increased = false;
+ set_mf_get_page_status(gp_status, MF_GET_PAGE_OK);
+
if (flags & MF_COUNT_INCREASED)
count_increased = true;
@@ -1406,11 +1424,13 @@ static int get_any_page(struct page *p, unsigned long flags)
if (pass++ < GET_PAGE_MAX_RETRY_NUM)
goto try_again;
ret = -EBUSY;
+ set_mf_get_page_status(gp_status, MF_GET_PAGE_RACE);
} else if (!PageHuge(p) && !is_free_buddy_page(p)) {
/* We raced with put_page, retry. */
if (pass++ < GET_PAGE_MAX_RETRY_NUM)
goto try_again;
ret = -EIO;
+ set_mf_get_page_status(gp_status, MF_GET_PAGE_RACE);
}
goto out;
} else if (ret == -EBUSY) {
@@ -1423,6 +1443,7 @@ static int get_any_page(struct page *p, unsigned long flags)
goto try_again;
}
ret = -EIO;
+ set_mf_get_page_status(gp_status, MF_GET_PAGE_UNHANDLABLE);
goto out;
}
}
@@ -1442,6 +1463,7 @@ static int get_any_page(struct page *p, unsigned long flags)
}
put_page(p);
ret = -EIO;
+ set_mf_get_page_status(gp_status, MF_GET_PAGE_UNHANDLABLE);
}
out:
if (ret == -EIO)
@@ -1480,6 +1502,7 @@ static int __get_unpoison_page(struct page *page)
* get_hwpoison_page() - Get refcount for memory error handling
* @p: Raw error page (hit by memory error)
* @flags: Flags controlling behavior of error handling
+ * @gp_status: Optional output for the reason get_any_page() failed
*
* get_hwpoison_page() takes a page refcount of an error page to handle memory
* error on it, after checking that the error page is in a well-defined state
@@ -1503,7 +1526,8 @@ static int __get_unpoison_page(struct page *page)
* operations like allocation and free,
* -EHWPOISON when the page is hwpoisoned and taken off from buddy.
*/
-static int get_hwpoison_page(struct page *p, unsigned long flags)
+static int get_hwpoison_page(struct page *p, unsigned long flags,
+ enum mf_get_page_status *gp_status)
{
int ret;
@@ -1511,7 +1535,7 @@ static int get_hwpoison_page(struct page *p, unsigned long flags)
if (flags & MF_UNPOISON)
ret = __get_unpoison_page(p);
else
- ret = get_any_page(p, flags);
+ ret = get_any_page(p, flags, gp_status);
zone_pcp_enable(page_zone(p));
return ret;
@@ -2349,6 +2373,7 @@ int memory_failure(unsigned long pfn, int flags)
bool retry = true;
int hugetlb = 0;
bool is_reserved;
+ enum mf_get_page_status gp_status = MF_GET_PAGE_OK;
if (!sysctl_memory_failure_recovery)
panic("Memory failure on page %lx", pfn);
@@ -2424,7 +2449,7 @@ int memory_failure(unsigned long pfn, int flags)
*/
is_reserved = PageReserved(p);
- res = get_hwpoison_page(p, flags);
+ res = get_hwpoison_page(p, flags, &gp_status);
if (!res) {
if (is_free_buddy_page(p)) {
if (take_page_off_buddy(p)) {
@@ -2445,7 +2470,12 @@ int memory_failure(unsigned long pfn, int flags)
}
goto unlock_mutex;
} else if (res < 0) {
- if (is_reserved)
+ /*
+ * Promote a stable unhandlable kernel page diagnosed by
+ * get_hwpoison_page() to MF_MSG_KERNEL alongside reserved
+ * pages; transient lifecycle races stay as MF_MSG_GET_HWPOISON.
+ */
+ if (is_reserved || gp_status == MF_GET_PAGE_UNHANDLABLE)
res = action_result(pfn, MF_MSG_KERNEL, MF_IGNORED);
else
res = action_result(pfn, MF_MSG_GET_HWPOISON,
@@ -2750,7 +2780,7 @@ int unpoison_memory(unsigned long pfn)
goto unlock_mutex;
}
- ghp = get_hwpoison_page(p, MF_UNPOISON);
+ ghp = get_hwpoison_page(p, MF_UNPOISON, NULL);
if (!ghp) {
if (folio_test_hugetlb(folio)) {
huge = true;
@@ -2957,7 +2987,7 @@ int soft_offline_page(unsigned long pfn, int flags)
retry:
get_online_mems();
- ret = get_hwpoison_page(page, flags | MF_SOFT_OFFLINE);
+ ret = get_hwpoison_page(page, flags | MF_SOFT_OFFLINE, NULL);
put_online_mems();
if (hwpoison_filter(page)) {
--
2.53.0-Meta
^ permalink raw reply related
* [PATCH v6 3/4] mm/memory-failure: add panic option for unrecoverable pages
From: Breno Leitao @ 2026-05-11 15:38 UTC (permalink / raw)
To: Miaohe Lin, Naoya Horiguchi, Andrew Morton, Jonathan Corbet,
Shuah Khan, David Hildenbrand, Lorenzo Stoakes, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan,
Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
Liam R. Howlett
Cc: linux-mm, linux-kernel, linux-doc, linux-kselftest, Breno Leitao,
linux-trace-kernel, kernel-team
In-Reply-To: <20260511-ecc_panic-v6-0-183012ba7d4b@debian.org>
Add a sysctl panic_on_unrecoverable_memory_failure that triggers a
kernel panic when memory_failure() encounters pages that cannot be
recovered. This provides a clean crash with useful debug information
rather than allowing silent data corruption or a delayed crash at an
unrelated code path.
Panic eligibility is intentionally narrow: only MF_MSG_KERNEL with
result == MF_IGNORED panics. That covers reserved pages (PageReserved)
and the kernel page types that the prior patch promotes from
MF_MSG_GET_HWPOISON via MF_GET_PAGE_UNHANDLABLE — slab, vmalloc, page
tables, kernel stacks, and similar non-LRU/non-buddy kernel-owned pages.
All other action types are excluded:
- MF_MSG_GET_HWPOISON and MF_MSG_KERNEL_HIGH_ORDER can be reached by
transient refcount races with the page allocator (an in-flight buddy
allocation has refcount 0 and is no longer on the buddy free list,
briefly), and panicking on them would risk killing the box for what
is actually a recoverable userspace page.
- MF_MSG_UNKNOWN means identify_page_state() could not classify the
page; that is precisely the wrong basis for a panic decision.
Signed-off-by: Breno Leitao <leitao@debian.org>
---
mm/memory-failure.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 4210173060aac..e4a9ceacaf36b 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -74,6 +74,8 @@ static int sysctl_memory_failure_recovery __read_mostly = 1;
static int sysctl_enable_soft_offline __read_mostly = 1;
+static int sysctl_panic_on_unrecoverable_mf __read_mostly;
+
atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
static bool hw_memory_failure __read_mostly = false;
@@ -155,6 +157,15 @@ static const struct ctl_table memory_failure_table[] = {
.proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
+ },
+ {
+ .procname = "panic_on_unrecoverable_memory_failure",
+ .data = &sysctl_panic_on_unrecoverable_mf,
+ .maxlen = sizeof(sysctl_panic_on_unrecoverable_mf),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE,
}
};
@@ -1281,6 +1292,18 @@ static void update_per_node_mf_stats(unsigned long pfn,
++mf_stats->total;
}
+static bool panic_on_unrecoverable_mf(enum mf_action_page_type type,
+ enum mf_result result)
+{
+ if (!sysctl_panic_on_unrecoverable_mf || result != MF_IGNORED)
+ return false;
+
+ if (type == MF_MSG_KERNEL)
+ return true;
+
+ return false;
+}
+
/*
* "Dirty/Clean" indication is not 100% accurate due to the possibility of
* setting PG_dirty outside page lock. See also comment above set_page_dirty().
@@ -1298,6 +1321,9 @@ static int action_result(unsigned long pfn, enum mf_action_page_type type,
pr_err("%#lx: recovery action for %s: %s\n",
pfn, action_page_types[type], action_name[result]);
+ if (panic_on_unrecoverable_mf(type, result))
+ panic("Memory failure: %#lx: unrecoverable page", pfn);
+
return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;
}
--
2.53.0-Meta
^ permalink raw reply related
* [PATCH v6 4/4] Documentation: document panic_on_unrecoverable_memory_failure sysctl
From: Breno Leitao @ 2026-05-11 15:38 UTC (permalink / raw)
To: Miaohe Lin, Naoya Horiguchi, Andrew Morton, Jonathan Corbet,
Shuah Khan, David Hildenbrand, Lorenzo Stoakes, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan,
Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
Liam R. Howlett
Cc: linux-mm, linux-kernel, linux-doc, linux-kselftest, Breno Leitao,
linux-trace-kernel, kernel-team
In-Reply-To: <20260511-ecc_panic-v6-0-183012ba7d4b@debian.org>
Add documentation for the new vm.panic_on_unrecoverable_memory_failure
sysctl, describing which failures trigger a panic (kernel-owned pages
the handler cannot recover) and which are intentionally left out
(transient allocator races and unclassified pages).
Signed-off-by: Breno Leitao <leitao@debian.org>
---
Documentation/admin-guide/sysctl/vm.rst | 70 +++++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 97e12359775c9..802c51ba8c43b 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -67,6 +67,7 @@ Currently, these files are in /proc/sys/vm:
- page-cluster
- page_lock_unfairness
- panic_on_oom
+- panic_on_unrecoverable_memory_failure
- percpu_pagelist_high_fraction
- stat_interval
- stat_refresh
@@ -925,6 +926,75 @@ panic_on_oom=2+kdump gives you very strong tool to investigate
why oom happens. You can get snapshot.
+panic_on_unrecoverable_memory_failure
+======================================
+
+When a hardware memory error (e.g. multi-bit ECC) hits a kernel page
+that cannot be recovered by the memory failure handler, the default
+behaviour is to ignore the error and continue operation. This is
+dangerous because the corrupted data remains accessible to the kernel,
+risking silent data corruption or a delayed crash when the poisoned
+memory is next accessed.
+
+When enabled, this sysctl triggers a panic on kernel-owned pages that
+the memory failure handler cannot recover: reserved pages
+(``PageReserved``) and stable kernel pages that hwpoison cannot handle
+(slab, vmalloc, page tables, kernel stacks, and similar non-LRU,
+non-buddy pages).
+
+Other failure paths are intentionally left out because they can be
+reached by transient races with the page allocator (an in-flight
+buddy allocation has refcount 0 and is no longer on the buddy free
+list, briefly), and panicking on them would risk killing the box for
+a page that was actually destined for userspace where the standard
+SIGBUS recovery path applies. Pages whose state could not be
+classified at all are also not covered, since an unknown state is
+not a sound basis for a panic decision.
+
+For many environments it is preferable to panic immediately with a clean
+crash dump that captures the original error context, rather than to
+continue and face a random crash later whose cause is difficult to
+diagnose.
+
+Use cases
+---------
+
+This option is most useful in environments where unattributed crashes
+are expensive to debug or where data integrity must take precedence
+over availability:
+
+* Large fleets, where multi-bit ECC errors on kernel pages are observed
+ regularly and post-mortem analysis of an unrelated downstream crash
+ (often seconds to minutes after the original error) consumes
+ significant engineering effort.
+
+* Systems configured with kdump, where panicking at the moment of the
+ hardware error produces a vmcore that still contains the faulting
+ address, the affected page state, and the originating MCE/GHES
+ record — context that is typically lost by the time a delayed crash
+ occurs.
+
+* High-availability clusters that rely on fast, deterministic node
+ failure for failover, and prefer an immediate panic over silent data
+ corruption propagating to replicas or persistent storage.
+
+* Kernel and platform developers reproducing hwpoison issues with
+ tools such as ``mce-inject`` or error-injection debugfs interfaces,
+ where panicking on the unrecoverable path makes regressions
+ immediately visible instead of surfacing as later, unrelated
+ failures.
+
+= =====================================================================
+0 Try to continue operation (default).
+1 Panic immediately. If the ``panic`` sysctl is also non-zero then the
+ machine will be rebooted.
+= =====================================================================
+
+Example::
+
+ echo 1 > /proc/sys/vm/panic_on_unrecoverable_memory_failure
+
+
percpu_pagelist_high_fraction
=============================
--
2.53.0-Meta
^ permalink raw reply related
* Re: [PATCH v14 05/19] unwind_user/sframe: Add support for reading .sframe contents
From: Jens Remus @ 2026-05-11 16:16 UTC (permalink / raw)
To: Steven Rostedt, Josh Poimboeuf, Indu Bhagat, Dylan Hatch
Cc: bpf, linux-mm, linux-kernel, linux-trace-kernel, x86,
Namhyung Kim, Andrii Nakryiko, Jose E. Marchesi, Beau Belgrave,
Florian Weimer, Carlos O'Donell, Masami Hiramatsu, Jiri Olsa,
Arnaldo Carvalho de Melo, Andrew Morton, David Hildenbrand,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Heiko Carstens, Vasily Gorbik,
Ilya Leoshkevich, Steven Rostedt (Google), Peter Zijlstra,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen,
H. Peter Anvin, Mathieu Desnoyers, Kees Cook, Sam James
In-Reply-To: <20260505121718.3572346-6-jremus@linux.ibm.com>
On 5/5/2026 2:17 PM, Jens Remus wrote:
> From: Josh Poimboeuf <jpoimboe@kernel.org>
>
> In preparation for using sframe to unwind user space stacks, add an
> sframe_find() interface for finding the sframe information associated
> with a given text address.
>
> For performance, use user_read_access_begin() and the corresponding
> unsafe_*() accessors. Note that use of pr_debug() in uaccess-enabled
> regions would break noinstr validation, so there aren't any debug
> messages yet. That will be added in a subsequent commit.
>
> Link: https://lore.kernel.org/all/77c0d1ec143bf2a53d66c4ecb190e7e0a576fbfd.1737511963.git.jpoimboe@kernel.org/
> Link: https://lore.kernel.org/all/b35ca3a3-8de5-4d32-8d30-d4e562f6b0de@linux.ibm.com/
>
> [ Jens Remus: Add initial support for SFrame V3 (limited to regular
> FDEs). Add support for PC-relative FDE function start offset. Simplify
> logic by using an internal FDE representation. Rename struct sframe_fre
> to sframe_fre_internal to align with struct sframe_fde_internal.
> Cleanup includes. Fix checkpatch errors "spaces required around that
> ':'". ]
> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
It just occurred to me that that the use of the return values -EINVAL
and -EFAULT is inconsistent across __read_fde() and __read_fre():
-EINVAL is to be used when a lookup for an IP fails (i.e. cannot be
satisfied) and
-EFAULT is to be used when the .sframe is corrupted/inconsistent and
should be unregistered.
> +static __always_inline int __read_fde(struct sframe_section *sec,
> + unsigned int fde_num,
> + struct sframe_fde_internal *fde)
> +{
> + unsigned long fde_addr, fda_addr, func_addr;
> + struct sframe_fde_v3 _fde;
> + struct sframe_fda_v3 _fda;
> +
> + fde_addr = sec->fdes_start + (fde_num * sizeof(struct sframe_fde_v3));
> + unsafe_copy_from_user(&_fde, (void __user *)fde_addr,
> + sizeof(struct sframe_fde_v3), Efault);
> +
> + func_addr = fde_addr + _fde.func_start_off;
> + if (func_addr < sec->text_start || func_addr >= sec->text_end)
> + return -EINVAL;
return -EFAULT;
> +
> + fda_addr = sec->fres_start + _fde.fres_off;
> + if (fda_addr + sizeof(struct sframe_fda_v3) > sec->fres_end)
> + return -EINVAL;
return -EFAULT;
> + unsafe_copy_from_user(&_fda, (void __user *)fda_addr,
> + sizeof(struct sframe_fda_v3), Efault);
> +
> + fde->func_addr = func_addr;
> + fde->func_size = _fde.func_size;
> + fde->fda_off = _fde.fres_off;
> + fde->fres_off = _fde.fres_off + sizeof(struct sframe_fda_v3);
> + fde->fres_num = _fda.fres_num;
> + fde->info = _fda.info;
> + fde->info2 = _fda.info2;
> + fde->rep_size = _fda.rep_size;
> +
> + return 0;
> +
> +Efault:
> + return -EFAULT;
> +}
> +static __always_inline int __read_fre(struct sframe_section *sec,
> + struct sframe_fde_internal *fde,
> + unsigned long fre_addr,
> + struct sframe_fre_internal *fre)
> +{
> + unsigned char fde_type = SFRAME_V3_FDE_TYPE(fde->info2);
> + unsigned char fde_pctype = SFRAME_V3_FDE_PCTYPE(fde->info);
> + unsigned char fre_type = SFRAME_V3_FDE_FRE_TYPE(fde->info);
> + unsigned char dataword_count, dataword_size;
> + s32 cfa_off, ra_off, fp_off;
> + unsigned long cur = fre_addr;
> + unsigned char addr_size;
> + u32 ip_off;
> + u8 info;
> +
> + addr_size = fre_type_to_size(fre_type);
> + if (!addr_size)
> + return -EFAULT;
> +
> + if (fre_addr + addr_size + 1 > sec->fres_end)
> + return -EFAULT;
> +
> + UNSAFE_GET_USER_INC(ip_off, cur, addr_size, Efault);
> + if (fde_pctype == SFRAME_FDE_PCTYPE_INC && ip_off > fde->func_size)
> + return -EFAULT;
> +
> + UNSAFE_GET_USER_INC(info, cur, 1, Efault);
> + dataword_count = SFRAME_V3_FRE_DATAWORD_COUNT(info);
> + dataword_size = dataword_size_enum_to_size(SFRAME_V3_FRE_DATAWORD_SIZE(info));
> + if (!dataword_count || !dataword_size)
> + return -EFAULT;
> +
> + if (cur + (dataword_count * dataword_size) > sec->fres_end)
> + return -EFAULT;
> +
> + /* TODO: Support for flexible FDEs not implemented yet. */
> + if (fde_type != SFRAME_FDE_TYPE_DEFAULT)
> + return -EFAULT;
> +
> + UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
> + dataword_count--;
> +
> + ra_off = sec->ra_off;
> + if (!ra_off) {
> + if (!dataword_count--)
> + return -EFAULT;
> +
> + UNSAFE_GET_USER_INC(ra_off, cur, dataword_size, Efault);
> + }
> +
> + fp_off = sec->fp_off;
> + if (!fp_off && dataword_count) {
> + dataword_count--;
> + UNSAFE_GET_USER_INC(fp_off, cur, dataword_size, Efault);
> + }
> +
> + if (dataword_count)
> + return -EFAULT;
> +
> + fre->size = addr_size + 1 + (dataword_count * dataword_size);
> + fre->ip_off = ip_off;
> + fre->cfa_off = cfa_off;
> + fre->ra_off = ra_off;
> + fre->fp_off = fp_off;
> + fre->info = info;
> +
> + return 0;
> +
> +Efault:
> + return -EFAULT;
> +}
Similar for sframe_init_cfa_rule_data() (and sframe_init_rule_data())
that get introduced with subsequent commits.
Regards,
Jens
--
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com
IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/
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