* [PATCH v2] tracing: fix CFI violation in probestub test
From: Eva Kurchatova @ 2026-06-02 13:54 UTC (permalink / raw)
To: mhiramat, rostedt
Cc: linux-trace-kernel, linux-kernel, mathieu.desnoyers, peterz,
jpoimboe, samitolvanen, eva.kurchatova
When multiple callbacks are registered on the same tracepoint,
callbacks will be indirectly called via traceiter helper.
Pointers to __probestub_* callbacks reside in __tracepoints section,
which is excluded from ENDBR checks in objtool, causing objtool to
assume those functions are never indirectly called.
Registering multiple callbacks using sched_wakeup test will result
in #CP exception due to missing ENDBR in __probestub_sched_wakeup
on a CFI-enabled machine.
Fix this by adding CFI_NOSEAL annotation to probestub declaration.
Fixes: d5173f753750 ("objtool: Exclude __tracepoints data from ENDBR checks")
Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
---
include/linux/tracepoint.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 763eea4d80d8..38e9f49a71b7 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -20,6 +20,7 @@
#include <linux/rcupdate_trace.h>
#include <linux/tracepoint-defs.h>
#include <linux/static_call.h>
+#include <asm/cfi.h>
struct module;
struct tracepoint;
@@ -389,6 +390,13 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
void __probestub_##_name(void *__data, proto) \
{ \
} \
+ /* \
+ * Annotate the probestub 'CFI_NOSEAL' to stop objtool from \
+ * requesting the kernel remove the ENDBR, because the only \
+ * references to the function are in the __tracepoint section, \
+ * that objtool doesn't scan. \
+ */ \
+ CFI_NOSEAL(__probestub_##_name); \
DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name); \
DEFINE_RUST_DO_TRACE(_name, TP_PROTO(proto), TP_ARGS(args))
--
2.54.0
^ permalink raw reply related
* Re: [PATCH v2] tracing: fix CFI violation in probestub test
From: Masami Hiramatsu @ 2026-06-02 14:33 UTC (permalink / raw)
To: Eva Kurchatova
Cc: rostedt, linux-trace-kernel, linux-kernel, mathieu.desnoyers,
peterz, jpoimboe, samitolvanen
In-Reply-To: <20260602135425.542073-1-eva.kurchatova@virtuozzo.com>
On Tue, 2 Jun 2026 16:54:08 +0300
Eva Kurchatova <eva.kurchatova@virtuozzo.com> wrote:
> When multiple callbacks are registered on the same tracepoint,
> callbacks will be indirectly called via traceiter helper.
>
> Pointers to __probestub_* callbacks reside in __tracepoints section,
> which is excluded from ENDBR checks in objtool, causing objtool to
> assume those functions are never indirectly called.
>
> Registering multiple callbacks using sched_wakeup test will result
> in #CP exception due to missing ENDBR in __probestub_sched_wakeup
> on a CFI-enabled machine.
>
> Fix this by adding CFI_NOSEAL annotation to probestub declaration.
>
Thanks, this looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Fixes: d5173f753750 ("objtool: Exclude __tracepoints data from ENDBR checks")
> Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
> ---
> include/linux/tracepoint.h | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 763eea4d80d8..38e9f49a71b7 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -20,6 +20,7 @@
> #include <linux/rcupdate_trace.h>
> #include <linux/tracepoint-defs.h>
> #include <linux/static_call.h>
> +#include <asm/cfi.h>
>
> struct module;
> struct tracepoint;
> @@ -389,6 +390,13 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> void __probestub_##_name(void *__data, proto) \
> { \
> } \
> + /* \
> + * Annotate the probestub 'CFI_NOSEAL' to stop objtool from \
> + * requesting the kernel remove the ENDBR, because the only \
> + * references to the function are in the __tracepoint section, \
> + * that objtool doesn't scan. \
> + */ \
> + CFI_NOSEAL(__probestub_##_name); \
> DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name); \
> DEFINE_RUST_DO_TRACE(_name, TP_PROTO(proto), TP_ARGS(args))
>
> --
> 2.54.0
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply
* [PATCH 1/2] tracing: work around -Wmissing-format-attribute warning
From: Arnd Bergmann @ 2026-06-02 15:07 UTC (permalink / raw)
To: Steven Rostedt, Masami Hiramatsu, Andrew Morton, Petr Mladek,
Nathan Chancellor
Cc: Arnd Bergmann, Dennis Dalessandro, Jason Gunthorpe,
Leon Romanovsky, Arend van Spriel, Miri Korenblit,
Mathieu Desnoyers, Andy Shevchenko, Rasmus Villemoes,
Sergey Senozhatsky, Nick Desaulniers, Bill Wendling, Justin Stitt,
Vlastimil Babka, linux-rdma, linux-kernel, linux-wireless,
brcm80211, brcm80211-dev-list.pdl, linux-trace-kernel, llvm
From: Arnd Bergmann <arnd@arndb.de>
A number of tracing headers turn off -Wsuggest-attribute=format for
gcc, but they don't turn it off for clang, so the same warning still
happens on new versions of clang that support the format attribute.
To avoid duplicating the same thing in each tracing header, as well
as changing all of them to also turn it off for clang, add a new
__vsnprintf() helper that is not annotated this way in linux/sprintf.h
but is defined to work the same way as the regular vsprintf.
Aside from tracing, the same thing can be used in va_format(),
which is part of lib/vsprintf.c itself.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
This version is a fairly simplistic way to work around the warning
reliably. I have resent two more patches to address actually
missing annotations in device drivers, but with all of these
out of the way, we can move the warning from the 'make W=1'
into the default set.
I have also prototyped a variant of this patch that passes down
a 'struct va_format' throughout the tracing code. That patch is
a little more invasive and I have no idea if that actually works,
but the result looks simpler.
---
drivers/infiniband/hw/hfi1/trace_dbg.h | 7 -------
.../broadcom/brcm80211/brcmfmac/tracepoint.h | 7 -------
.../brcm80211/brcmsmac/brcms_trace_brcmsmac_msg.h | 7 -------
drivers/net/wireless/intel/iwlwifi/iwl-devtrace.c | 3 ---
include/linux/sprintf.h | 1 +
include/linux/trace_events.h | 2 +-
include/trace/events/qla.h | 7 -------
include/trace/stages/stage6_event_callback.h | 2 +-
lib/vsprintf.c | 12 +++++++-----
samples/trace_events/trace-events-sample.c | 2 --
10 files changed, 10 insertions(+), 40 deletions(-)
diff --git a/drivers/infiniband/hw/hfi1/trace_dbg.h b/drivers/infiniband/hw/hfi1/trace_dbg.h
index 58304b91380f..05c4f1354269 100644
--- a/drivers/infiniband/hw/hfi1/trace_dbg.h
+++ b/drivers/infiniband/hw/hfi1/trace_dbg.h
@@ -22,11 +22,6 @@
#define MAX_MSG_LEN 512
-#pragma GCC diagnostic push
-#ifndef __clang__
-#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
-#endif
-
DECLARE_EVENT_CLASS(hfi1_trace_template,
TP_PROTO(const char *function, struct va_format *vaf),
TP_ARGS(function, vaf),
@@ -41,8 +36,6 @@ DECLARE_EVENT_CLASS(hfi1_trace_template,
__get_str(msg))
);
-#pragma GCC diagnostic pop
-
/*
* It may be nice to macroize the __hfi1_trace but the va_* stuff requires an
* actual function to work and can not be in a macro.
diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/tracepoint.h b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/tracepoint.h
index 96032322b165..6c4e00e9ccd1 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/tracepoint.h
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/tracepoint.h
@@ -28,11 +28,6 @@ static inline void trace_ ## name(proto) {}
#define MAX_MSG_LEN 100
-#pragma GCC diagnostic push
-#ifndef __clang__
-#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
-#endif
-
TRACE_EVENT(brcmf_err,
TP_PROTO(const char *func, struct va_format *vaf),
TP_ARGS(func, vaf),
@@ -128,8 +123,6 @@ TRACE_EVENT(brcmf_sdpcm_hdr,
__entry->len, ((u8 *)__get_dynamic_array(hdr))[4])
);
-#pragma GCC diagnostic pop
-
#ifdef CONFIG_BRCM_TRACING
#undef TRACE_INCLUDE_PATH
diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmsmac/brcms_trace_brcmsmac_msg.h b/drivers/net/wireless/broadcom/brcm80211/brcmsmac/brcms_trace_brcmsmac_msg.h
index 908ce3c864fe..dc296d8bf775 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmsmac/brcms_trace_brcmsmac_msg.h
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmsmac/brcms_trace_brcmsmac_msg.h
@@ -24,11 +24,6 @@
#define MAX_MSG_LEN 100
-#pragma GCC diagnostic push
-#ifndef __clang__
-#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
-#endif
-
DECLARE_EVENT_CLASS(brcms_msg_event,
TP_PROTO(struct va_format *vaf),
TP_ARGS(vaf),
@@ -77,8 +72,6 @@ TRACE_EVENT(brcms_dbg,
TP_printk("%s: %s", __get_str(func), __get_str(msg))
);
-#pragma GCC diagnostic pop
-
#endif /* __TRACE_BRCMSMAC_MSG_H */
#ifdef CONFIG_BRCM_TRACING
diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-devtrace.c b/drivers/net/wireless/intel/iwlwifi/iwl-devtrace.c
index 7e686297963d..49a8196430a7 100644
--- a/drivers/net/wireless/intel/iwlwifi/iwl-devtrace.c
+++ b/drivers/net/wireless/intel/iwlwifi/iwl-devtrace.c
@@ -12,9 +12,6 @@
#include "iwl-trans.h"
#define CREATE_TRACE_POINTS
-#ifdef CONFIG_CC_IS_GCC
-#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
-#endif
#include "iwl-devtrace.h"
EXPORT_TRACEPOINT_SYMBOL(iwlwifi_dev_ucode_event);
diff --git a/include/linux/sprintf.h b/include/linux/sprintf.h
index f06f7b785091..036a247b7c1e 100644
--- a/include/linux/sprintf.h
+++ b/include/linux/sprintf.h
@@ -12,6 +12,7 @@ __printf(2, 3) int sprintf(char *buf, const char * fmt, ...);
__printf(2, 0) int vsprintf(char *buf, const char *, va_list);
__printf(3, 4) int snprintf(char *buf, size_t size, const char *fmt, ...);
__printf(3, 0) int vsnprintf(char *buf, size_t size, const char *fmt, va_list args);
+int __vsnprintf(char *buf, size_t size, const char *fmt, va_list args);
__printf(3, 4) int scnprintf(char *buf, size_t size, const char *fmt, ...);
__printf(3, 0) int vscnprintf(char *buf, size_t size, const char *fmt, va_list args);
__printf(2, 3) __malloc char *kasprintf(gfp_t gfp, const char *fmt, ...);
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index d49338c44014..4715330c7b6b 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -962,7 +962,7 @@ perf_trace_buf_submit(void *raw_data, int size, int rctx, u16 type,
int __ret; \
\
va_copy(__ap, *(va)); \
- __ret = vsnprintf(NULL, 0, fmt, __ap) + 1; \
+ __ret = __vsnprintf(NULL, 0, fmt, __ap) + 1; \
va_end(__ap); \
\
min(__ret, TRACE_EVENT_STR_MAX); \
diff --git a/include/trace/events/qla.h b/include/trace/events/qla.h
index 8800c35525a1..74a7534b99b6 100644
--- a/include/trace/events/qla.h
+++ b/include/trace/events/qla.h
@@ -9,11 +9,6 @@
#define QLA_MSG_MAX 256
-#pragma GCC diagnostic push
-#ifndef __clang__
-#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
-#endif
-
DECLARE_EVENT_CLASS(qla_log_event,
TP_PROTO(const char *buf,
struct va_format *vaf),
@@ -32,8 +27,6 @@ DECLARE_EVENT_CLASS(qla_log_event,
TP_printk("%s %s", __get_str(buf), __get_str(msg))
);
-#pragma GCC diagnostic pop
-
DEFINE_EVENT(qla_log_event, ql_dbg_log,
TP_PROTO(const char *buf, struct va_format *vaf),
TP_ARGS(buf, vaf)
diff --git a/include/trace/stages/stage6_event_callback.h b/include/trace/stages/stage6_event_callback.h
index 1691676fd858..7d6a6ca6e779 100644
--- a/include/trace/stages/stage6_event_callback.h
+++ b/include/trace/stages/stage6_event_callback.h
@@ -45,7 +45,7 @@
do { \
va_list __cp_va; \
va_copy(__cp_va, *(va)); \
- vsnprintf(__get_str(dst), TRACE_EVENT_STR_MAX, fmt, __cp_va); \
+ __vsnprintf(__get_str(dst), TRACE_EVENT_STR_MAX, fmt, __cp_va); \
va_end(__cp_va); \
} while (0)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index a3017bc58986..3caf0796f54d 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1702,9 +1702,6 @@ char *escaped_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
return buf;
}
-__diag_push();
-__diag_ignore(GCC, all, "-Wsuggest-attribute=format",
- "Not a valid __printf() conversion candidate.");
static char *va_format(char *buf, char *end, struct va_format *va_fmt,
struct printf_spec spec)
{
@@ -1714,12 +1711,11 @@ static char *va_format(char *buf, char *end, struct va_format *va_fmt,
return buf;
va_copy(va, *va_fmt->va);
- buf += vsnprintf(buf, end > buf ? end - buf : 0, va_fmt->fmt, va);
+ buf += __vsnprintf(buf, end > buf ? end - buf : 0, va_fmt->fmt, va);
va_end(va);
return buf;
}
-__diag_pop();
static noinline_for_stack
char *uuid_string(char *buf, char *end, const u8 *addr,
@@ -2979,6 +2975,12 @@ int vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args)
}
EXPORT_SYMBOL(vsnprintf);
+int __printf(3, 0) __vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args)
+{
+ return vsnprintf(buf, size, fmt_str, args);
+}
+EXPORT_SYMBOL(__vsnprintf);
+
/**
* vscnprintf - Format a string and place it in a buffer
* @buf: The buffer to place the result into
diff --git a/samples/trace_events/trace-events-sample.c b/samples/trace_events/trace-events-sample.c
index 9993fb5d5f98..ecc7db237f2e 100644
--- a/samples/trace_events/trace-events-sample.c
+++ b/samples/trace_events/trace-events-sample.c
@@ -9,8 +9,6 @@
* creates the handles for the trace points.
*/
#define CREATE_TRACE_POINTS
-__diag_ignore(GCC, all, "-Wsuggest-attribute=format",
- "trace_event_get_offsets_foo_bar can't easily be annotated as __printf");
#include "trace-events-sample.h"
static const char *random_strings[] = {
--
2.39.5
^ permalink raw reply related
* [PATCH 2/2] tracing/osnoise: add printf attribute to osnoise_print
From: Arnd Bergmann @ 2026-06-02 15:07 UTC (permalink / raw)
To: Steven Rostedt, Masami Hiramatsu, Crystal Wood
Cc: Arnd Bergmann, Mathieu Desnoyers, Tomas Glozar, Wang Liang,
linux-kernel, linux-trace-kernel
In-Reply-To: <20260602150904.2258624-1-arnd@kernel.org>
From: Arnd Bergmann <arnd@arndb.de>
gcc points out that tne newly added function uses printf style arguments
and should get an attribute to allow verifying the format strings for
its callers:
kernel/trace/trace_osnoise.c: In function 'osnoise_print':
kernel/trace/trace_osnoise.c:96:17: error: function 'osnoise_print' might be a candidate for 'gnu_printf' format attribute [-Werror=suggest-attribute=format]
96 | trace_array_vprintk(tr, _RET_IP_, fmt, ap);
| ^~~~~~~~~~~~~~~~~~~
Add the attribute as suggested
Fixes: 9cb99c598643 ("tracing/osnoise: Array printk init and cleanup")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
kernel/trace/trace_osnoise.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 1fbd8525ab54..6fa015e57899 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -83,7 +83,7 @@ struct osnoise_instance {
static struct list_head osnoise_instances;
-static void osnoise_print(const char *fmt, ...)
+static __printf(1, 2) void osnoise_print(const char *fmt, ...)
{
struct osnoise_instance *inst;
struct trace_array *tr;
--
2.39.5
^ permalink raw reply related
* Re: [PATCH mm-unstable v18 06/14] mm/khugepaged: generalize collapse_huge_page for mTHP collapse
From: Nico Pache @ 2026-06-02 15:30 UTC (permalink / raw)
To: Lance Yang
Cc: David Hildenbrand (Arm), linux-doc, linux-kernel, linux-mm,
linux-trace-kernel, aarcange, akpm, anshuman.khandual, apopple,
baohua, baolin.wang, byungchul, catalin.marinas, cl, corbet,
dave.hansen, dev.jain, gourry, hannes, hughd, jack, jackmanb,
jannh, jglisse, joshua.hahnjy, kas, liam, ljs, mathieu.desnoyers,
matthew.brost, mhiramat, mhocko, peterx, pfalcato, rakie.kim,
raquini, rdunlap, richard.weiyang, rientjes, rostedt, rppt,
ryan.roberts, shivankg, sunnanyong, surenb, thomas.hellstrom,
tiwai, usamaarif642, vbabka, vishal.moola, wangkefeng.wang, will,
willy, yang, ying.huang, ziy, zokeefe, usama.arif
In-Reply-To: <baa0a462-46e0-44ab-b583-c722ad253afe@linux.dev>
On Mon, Jun 1, 2026 at 4:48 AM Lance Yang <lance.yang@linux.dev> wrote:
>
>
>
> On 2026/6/1 18:23, David Hildenbrand (Arm) wrote:
> > On 6/1/26 11:08, Lance Yang wrote:
> >>
> >>
> >> On 2026/6/1 14:54, David Hildenbrand (Arm) wrote:
> >>> On 6/1/26 05:28, Lance Yang wrote:
> >>>>
> >>>>
> >>>> Ah, fair point.
> >>>>
> >>>> I was mostly worried about arch hooks that walk vma->vm_mm again, rather
> >>>> than only using the pte pointer passed in. For example, mips does:
> >>>
> >>> Right, a re-walk would be the real problem.
> >>>
> >>>>
> >>>> update_mmu_cache_range()
> >>>> -> __update_tlb()
> >>>> -> pgd_offset(vma->vm_mm, address)
> >>>> -> pte_offset_map(...)
> >>>>
> >>>> and __update_tlb() has this assumption:
> >>>>
> >>>> /*
> >>>> * update_mmu_cache() is called between pte_offset_map_lock()
> >>>> * and pte_unmap_unlock(), so we can assume that ptep is not
> >>>> * NULL here: and what should be done below if it were NULL?
> >>>> */
> >>>>
> >>>> So if khugepaged happens to run with current->active_mm == vma->vm_mm
> >>>> here, could __update_tlb() hit the none PMD, get NULL from
> >>>> pte_offset_map(), and then dereference it?
> >>>
> >>> Likely yes -- that MIPS code is horrible. And the comment in MIPS code
> >>> even spells that out. :(
> >>>
> >>> Do you know about other code like that, or is MIPS the only one doing a
> >>> re-walk and crossing fingers?
> >>>
> >>>>
> >>>> Just wanted to raise it since some arch code may still have assumptions
> >>>> like this, and the always-enable-mTHP work is getting closer ...
> >>>
> >>> Right. I assume set_pte_at() couldn't trigger something similar (re-walk) in
> >>> arch code,
> >>> because we simply provide the ptep. update_mmu_cache_range() only consumes the
> >>> pte.
> >>>
> >>>>
> >>>> Probably very very very hard to hit, though :)
> >>>
> >>> Delaying update_mmu_cache_range() is nasty, as we'd have to make sure that
> >>> nobody can interfere in the meantime ... and the PMD lock will not be sufficient.
> >>>
> >>> Maybe we could reinstall the page table with the cleared (none) entries while
> >>> still holding the PTL?
> >>>
> >>> Thinking out loud:
> >>>
> >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> >>> index 5ba298d420b7..e39b750b1e6f 100644
> >>> --- a/mm/khugepaged.c
> >>> +++ b/mm/khugepaged.c
> >>> @@ -1413,13 +1413,17 @@ static enum scan_result collapse_huge_page(struct
> >>> mm_struct *mm, unsigned long s
> >>> map_anon_folio_pmd_nopf(folio, pmd, vma, pmd_addr);
> >>> } else {
> >>> /*
> >>> - * set_ptes is called in map_anon_folio_pte_nopf with the
> >>> - * pmd_ptl lock still held; this is safe as the PMD is expected
> >>> - * to be none. The pmd entry is then repopulated below.
> >>> + * Re-insert the page table with the cleared entries, but
> >>> + * hold the PTL, such that no one can mess with the re-installed
> >>> + * page table until we updated the temporarily-cleared entries
> >>> + * through map_anon_folio_pte_nopf().
> >>> */
> >>> - map_anon_folio_pte_nopf(folio, pte, vma, start_addr, /
> >>> *uffd_wp=*/ false);
> >>> - smp_wmb(); /* make PTEs visible before PMD. See pmd_install() */
> >>
> >> One small thing, I think we should probably keep the smp_wmb(), and just
> >> move it before the earlier pmd_populate().
> >>
> >> IIUC, the ordering we want is still:
> >>
> >> clear old PTEs
> >> smp_wmb()
> >> pmd_populate()
> >>
> >> so another CPU cannot walk through the re-installed PMD and still observe
> >> the old PTEs, right?
> >
> > There is a smp_wmb() in __folio_mark_uptodate(), that should be sufficient?
>
> Ah, cool! __folio_mark_uptodate() already does the job :P
>
> So yeah, no extra smp_wmb() needed here!
are we sure? that folio_mark_uptodate is done before the PTEs are
reinstalled. Then we reinstall the PMD right after. Currently
separated by the smp_wmb().
I was copying this from other THP code that performs similar PTE/PMD juggling.
I can remove it, but I'd rather air on the side of caution with this.
>
> Cheers, Lance
>
^ permalink raw reply
* Re: [PATCH 1/2] tracing: work around -Wmissing-format-attribute warning
From: Steven Rostedt @ 2026-06-02 15:40 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Masami Hiramatsu, Andrew Morton, Petr Mladek, Nathan Chancellor,
Arnd Bergmann, Dennis Dalessandro, Jason Gunthorpe,
Leon Romanovsky, Arend van Spriel, Miri Korenblit,
Mathieu Desnoyers, Andy Shevchenko, Rasmus Villemoes,
Sergey Senozhatsky, Nick Desaulniers, Bill Wendling, Justin Stitt,
Vlastimil Babka, linux-rdma, linux-kernel, linux-wireless,
brcm80211, brcm80211-dev-list.pdl, linux-trace-kernel, llvm
In-Reply-To: <20260602150904.2258624-1-arnd@kernel.org>
On Tue, 2 Jun 2026 17:07:05 +0200
Arnd Bergmann <arnd@kernel.org> wrote:
> @@ -2979,6 +2975,12 @@ int vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args)
> }
> EXPORT_SYMBOL(vsnprintf);
>
Should add a comment here for why this is needed.
-- Steve
> +int __printf(3, 0) __vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args)
> +{
> + return vsnprintf(buf, size, fmt_str, args);
> +}
> +EXPORT_SYMBOL(__vsnprintf);
> +
^ permalink raw reply
* Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support
From: Lance Yang @ 2026-06-02 15:44 UTC (permalink / raw)
To: Nico Pache
Cc: linux-doc, linux-kernel, linux-mm, linux-trace-kernel, aarcange,
akpm, anshuman.khandual, apopple, baohua, baolin.wang, byungchul,
catalin.marinas, cl, corbet, dave.hansen, david, dev.jain, gourry,
hannes, hughd, jack, jackmanb, jannh, jglisse, joshua.hahnjy, kas,
liam, ljs, mathieu.desnoyers, matthew.brost, mhiramat, mhocko,
peterx, pfalcato, rakie.kim, raquini, rdunlap, richard.weiyang,
rientjes, rostedt, rppt, ryan.roberts, shivankg, sunnanyong,
surenb, thomas.hellstrom, tiwai, usamaarif642, vbabka,
vishal.moola, wangkefeng.wang, will, willy, yang, ying.huang, ziy,
zokeefe
In-Reply-To: <CAA1CXcA+oZmp=cxiC2_EBDxqGX94gAd335d9eFPNv=j_0=og7Q@mail.gmail.com>
On 2026/6/2 18:58, Nico Pache wrote:
> On Sun, May 31, 2026 at 1:19 AM Lance Yang <lance.yang@linux.dev> wrote:
>>
>>
>> On Fri, May 22, 2026 at 09:00:06AM -0600, Nico Pache wrote:
>> [...]
>>> @@ -1587,10 +1749,11 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm,
>>> if (result == SCAN_SUCCEED) {
>>> /* collapse_huge_page expects the lock to be dropped before calling */
>>> mmap_read_unlock(mm);
>>> - result = collapse_huge_page(mm, start_addr, referenced,
>>> - unmapped, cc, HPAGE_PMD_ORDER);
>>> - /* collapse_huge_page will return with the mmap_lock released */
>>> + nr_collapsed = mthp_collapse(mm, vma, start_addr, referenced,
>>> + unmapped, cc, enabled_orders);
>>> + /* mmap_lock was released above, set lock_dropped */
>>> *lock_dropped = true;
>>> + result = nr_collapsed ? SCAN_SUCCEED : SCAN_FAIL;
>>
>> Hmm ... don't we lose the allocation-failure result here?
>>
>> Previously collapse_scan_pmd() propagated SCAN_ALLOC_HUGE_PAGE_FAIL from
>> collapse_huge_page(), so khugepaged would call khugepaged_alloc_sleep()
>> in khugepaged_do_scan().
>>
>> Now if allocation fails and nr_collapsed stays 0, we just return
>> SCAN_FAIL. So we won't back off via khugepaged_alloc_sleep() anymore?
>
> Ok I did the error propagation! I think I handled both of these cases
> you brought up pretty easily.
Thanks.
> However I don't know what to do in the following case: We successfully
> collapsed some portion of the PMD, but during that process, we also
> hit an allocation failure. Is it best to back off entirely? or can we
> treat some forward progress as a sign we can continue trying collapses
> without sleeping.
>
> Basically, do we prioritize SCAN_ALLOC_HUGE_PAGE_FAIL or the
> successful collapses as the returned value?
Thinking out loud, forward progress should win here, the allocation
failure only matter if we made no progress at all?
> This is what I currently have:
> done:
> if (collapsed)
> return SCAN_SUCCEED;
> if (alloc_failed)
> return SCAN_ALLOC_HUGE_PAGE_FAIL;
I'd go with this ordering :)
Cheers, Lance
^ permalink raw reply
* [PATCH 0/2] rtla: Add tests for option parsing with attached arguments
From: John Kacur @ 2026-06-02 15:52 UTC (permalink / raw)
To: linux-trace-kernel; +Cc: Steven Rostedt, Tomas Glozar, linux-kernel
This patch series adds comprehensive tests to verify that short options
with attached numeric arguments (e.g., -p100) work correctly across all
rtla commands.
These tests complement Tomas Glozar's fix "rtla: Fix parsing of
multi-character short options" which resolves the issue where options
like -p100 were incorrectly parsed as multiple separate options due to
getopt_long() being called twice.
The tests verify four option formats for each command:
-p 100 (short with space)
-p100 (short attached - previously broken)
--period=100 (long with equals)
--period 100 (long with space)
Commands tested:
- timerlat hist and top
- osnoise hist and top
- hwnoise
All 20 tests pass with Tomas's fix applied, confirming the issue is
resolved and preventing future regressions. These tests will continue to
work when rtla transitions to libsubcmd in the future, ensuring this
functionality remains correct across parsing implementations.
Note: Patch 1/2 is a resend of the timerlat hist tests sent previously.
Patch 2/2 adds tests for the remaining rtla commands.
Signed-off-by: John Kacur <jkacur@redhat.com>
John Kacur (2):
rtla/timerlat: Add tests for option parsing with attached arguments
rtla: Add tests for option parsing with attached arguments
tools/tracing/rtla/tests/hwnoise.t | 10 ++++++++++
tools/tracing/rtla/tests/osnoise.t | 18 ++++++++++++++++++
tools/tracing/rtla/tests/timerlat.t | 18 ++++++++++++++++++
3 files changed, 46 insertions(+)
--
2.54.0
^ permalink raw reply
* [PATCH 1/2] rtla/timerlat: Add tests for option parsing with attached arguments
From: John Kacur @ 2026-06-02 15:52 UTC (permalink / raw)
To: linux-trace-kernel; +Cc: Steven Rostedt, Tomas Glozar, linux-kernel
In-Reply-To: <20260602155210.60439-1-jkacur@redhat.com>
Add tests to verify that numeric arguments work correctly with both
attached and detached formats:
-p 100 (short with space)
-p100 (short without space)
--period=100 (long with =)
--period 100 (long with space)
These tests prevent regression of the bug fixed in commit eefa8af46ff7
("rtla/timerlat: Fix parsing of short options with attached arguments")
where -p100 was incorrectly parsed as multiple separate options.
The tests verify that:
1. All four argument formats succeed (exit code 0)
2. None trigger the "no-irq and no-thread" error that occurred when
the bug was present
Assisted-by: Claude:claude-sonnet-4-5
Signed-off-by: John Kacur <jkacur@redhat.com>
---
tools/tracing/rtla/tests/timerlat.t | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/tools/tracing/rtla/tests/timerlat.t b/tools/tracing/rtla/tests/timerlat.t
index fd4935fd7b49..1a63301f5d70 100644
--- a/tools/tracing/rtla/tests/timerlat.t
+++ b/tools/tracing/rtla/tests/timerlat.t
@@ -42,6 +42,16 @@ check "verify -c/--cpus" \
check "hist test in nanoseconds" \
"timerlat hist -i 2 -c 0 -n -d 10s" 2 "ns"
+# Option parsing tests - verify attached numeric arguments work correctly
+check "verify -p with space" \
+ "timerlat hist -p 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify -p without space (attached argument)" \
+ "timerlat hist -p100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify --period with equals" \
+ "timerlat hist --period=100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify --period with space" \
+ "timerlat hist --period 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+
# Actions tests
check "trace output through -t" \
"timerlat hist -T 2 -t" 2 "^ Saving trace to timerlat_trace.txt$"
--
2.54.0
^ permalink raw reply related
* [PATCH 2/2] rtla: Add tests for option parsing with attached arguments
From: John Kacur @ 2026-06-02 15:52 UTC (permalink / raw)
To: linux-trace-kernel; +Cc: Steven Rostedt, Tomas Glozar, linux-kernel
In-Reply-To: <20260602155210.60439-1-jkacur@redhat.com>
Add tests to verify that short options with attached numeric arguments
work correctly for all rtla commands after the parsing fixes.
Tests verify four formats for each command:
- Short option with space: -p 100
- Short option attached: -p100
- Long option with equals: --period=100
- Long option with space: --period 100
For osnoise and hwnoise commands, the tests also include -r 100 (runtime)
to satisfy the osnoise constraint that runtime <= period.
These tests complement the existing timerlat hist tests added in commit
d489b602c669 ("rtla/timerlat: Add tests for option parsing with attached
arguments").
Assisted-by: Claude:claude-sonnet-4-5
Signed-off-by: John Kacur <jkacur@redhat.com>
---
tools/tracing/rtla/tests/hwnoise.t | 10 ++++++++++
tools/tracing/rtla/tests/osnoise.t | 18 ++++++++++++++++++
tools/tracing/rtla/tests/timerlat.t | 8 ++++++++
3 files changed, 36 insertions(+)
diff --git a/tools/tracing/rtla/tests/hwnoise.t b/tools/tracing/rtla/tests/hwnoise.t
index 23ce250a6852..c61f02bc42fe 100644
--- a/tools/tracing/rtla/tests/hwnoise.t
+++ b/tools/tracing/rtla/tests/hwnoise.t
@@ -19,4 +19,14 @@ check "enable a trace event trigger" \
"hwnoise -t -e osnoise:irq_noise --trigger=\"hist:key=desc,duration:sort=desc,duration:vals=hitcount\" -d 10s" \
0 "Saving event osnoise:irq_noise hist to osnoise_irq_noise_hist.txt"
+# Option parsing tests - verify attached numeric arguments work correctly
+check "verify -p with space" \
+ "hwnoise -p 100 -r 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify -p without space (attached argument)" \
+ "hwnoise -p100 -r 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify --period with equals" \
+ "hwnoise --period=100 -r 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify --period with space" \
+ "hwnoise --period 100 -r 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+
test_end
diff --git a/tools/tracing/rtla/tests/osnoise.t b/tools/tracing/rtla/tests/osnoise.t
index 396334608920..1807236431df 100644
--- a/tools/tracing/rtla/tests/osnoise.t
+++ b/tools/tracing/rtla/tests/osnoise.t
@@ -17,6 +17,24 @@ check "verify the --trace param" \
check "verify the --entries/-E param" \
"osnoise hist -P F:1 -c 0 -r 900000 -d 10s -b 10 -E 25"
+# Option parsing tests - verify attached numeric arguments work correctly
+check "verify -p with space" \
+ "osnoise hist -p 100 -r 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify -p without space (attached argument)" \
+ "osnoise hist -p100 -r 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify --period with equals" \
+ "osnoise hist --period=100 -r 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify --period with space" \
+ "osnoise hist --period 100 -r 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify osnoise top -p with space" \
+ "osnoise top -p 100 -r 100 -c 0 -d 1s -q" 0 "" "no-irq and no-thread"
+check "verify osnoise top -p without space (attached argument)" \
+ "osnoise top -p100 -r 100 -c 0 -d 1s -q" 0 "" "no-irq and no-thread"
+check "verify osnoise top --period with equals" \
+ "osnoise top --period=100 -r 100 -c 0 -d 1s -q" 0 "" "no-irq and no-thread"
+check "verify osnoise top --period with space" \
+ "osnoise top --period 100 -r 100 -c 0 -d 1s -q" 0 "" "no-irq and no-thread"
+
# Test setting default period by putting an absurdly high period
# and stopping on threshold.
# If default period is not set, this will time out.
diff --git a/tools/tracing/rtla/tests/timerlat.t b/tools/tracing/rtla/tests/timerlat.t
index 1a63301f5d70..506227412027 100644
--- a/tools/tracing/rtla/tests/timerlat.t
+++ b/tools/tracing/rtla/tests/timerlat.t
@@ -51,6 +51,14 @@ check "verify --period with equals" \
"timerlat hist --period=100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
check "verify --period with space" \
"timerlat hist --period 100 -c 0 -d 1s" 0 "" "no-irq and no-thread"
+check "verify timerlat top -p with space" \
+ "timerlat top -p 100 -c 0 -d 1s -q" 0 "" "no-irq and no-thread"
+check "verify timerlat top -p without space (attached argument)" \
+ "timerlat top -p100 -c 0 -d 1s -q" 0 "" "no-irq and no-thread"
+check "verify timerlat top --period with equals" \
+ "timerlat top --period=100 -c 0 -d 1s -q" 0 "" "no-irq and no-thread"
+check "verify timerlat top --period with space" \
+ "timerlat top --period 100 -c 0 -d 1s -q" 0 "" "no-irq and no-thread"
# Actions tests
check "trace output through -t" \
--
2.54.0
^ permalink raw reply related
* Re: [PATCH v4 2/3] perf: enable unprivileged syscall tracing with perf trace
From: Anubhav Shelat @ 2026-06-02 16:12 UTC (permalink / raw)
To: Peter Zijlstra
Cc: mpetlan, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Mark Rutland,
Alexander Shishkin, Jiri Olsa, Ian Rogers, Adrian Hunter,
James Clark, Thomas Falcon, linux-kernel, linux-trace-kernel,
linux-perf-users
In-Reply-To: <20260518214116.GZ3102624@noisy.programming.kicks-ass.net>
On Mon, May 18, 2026 at 5:41 PM Peter Zijlstra <peterz@infradead.org> wrote:
> Typically patches are supposed to a single thing, you're listing 4
> things. What gives?
All four changes need to be made together to work properly. The second
point could be pulled out as a separate patch, but will be replaced
with the eventfs that Steve suggested. The other three points
represent a single logical change: selectively loosening the
perf_event_open() restrictions without exposing kernel data or
breaking uprobe functionality.
> PERF_SAMPLE_IP should be here too, no?
If PERF_SAMPLE_IP is added to the kaddr_leak mask it blocks uprobes,
so the PERF_SAMPLE_IP check is in the trace_event_perf.c changes where
I can exempt uprobes:
+ if ((p_event->attr.sample_type & PERF_SAMPLE_IP) &&
+ !p_event->attr.exclude_kernel &&
+ !(tp_event->flags & TRACE_EVENT_FL_UPROBE) &&
+ sysctl_perf_event_paranoid > 1 && !perfmon_capable())
+ return -EACCES;
> And I'm not sure if tracepoints can trigger it, but PHYS_ADDR also seems
> something we shouldn't allow.
There's a check for unprivileged access to PHYS_ADDR at core.c:13917
so I didn't add it to kaddr_leak.
> And we're sure RAW doesn't include pointers
PERF_SAMPLE_RAW for TRACE_EVENT_FL_CAP_ANY tracepoints doesn't include
kernel pointers.
> Again, you're doing the same thing in multiple places. If only there was
> something to re-use a previous expression.
>
> None of this gives me warm and fuzzy feelings.
You're right. I'll factor the checks out for the next version.
Anubhav
^ permalink raw reply
* Re: [PATCH] rtla: Fix parsing of multi-character short options
From: John Kacur @ 2026-06-02 16:21 UTC (permalink / raw)
To: Tomas Glozar; +Cc: linux-trace-kernel, Steven Rostedt, linux-kernel
In-Reply-To: <20260602125506.3325345-1-tglozar@redhat.com>
On Tue, 2 Jun 2026 14:55:06 +0200, Tomas Glozar wrote:
> rtla: Fix parsing of multi-character short options
Thanks for the fix! I've tested this patch with a comprehensive test suite
covering all rtla commands (timerlat hist/top, osnoise hist/top, hwnoise)
with the four option formats:
-p 100 (short with space)
-p100 (short attached - previously broken)
--period=100 (long with equals)
--period 100 (long with space)
All 20 tests pass. The fix correctly resolves the issue where -p100 was
being parsed as multiple separate options.
Tested-by: John Kacur <jkacur@redhat.com>
^ permalink raw reply
* Re: [syzbot] [trace?] KASAN: use-after-free Write in ring_buffer_read_page
From: Steven Rostedt @ 2026-06-02 16:28 UTC (permalink / raw)
To: syzbot
Cc: linux-kernel, linux-trace-kernel, mathieu.desnoyers, mhiramat,
syzkaller-bugs
In-Reply-To: <6a1ede7b.b4221f80.1326c5.0003.GAE@google.com>
On Tue, 02 Jun 2026 06:45:31 -0700
syzbot <syzbot+2dd9d02f60775ce5c1fb@syzkaller.appspotmail.com> wrote:
> syzbot found the following issue on:
>
> HEAD commit: e7ae89a0c97c Linux 7.1-rc5
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16f06e2e580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=58acee1ac5406016
> dashboard link: https://syzkaller.appspot.com/bug?extid=2dd9d02f60775ce5c1fb
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
>
> Unfortunately, I don't have any reproducer for this issue yet.
Looks like the test was doing something really weird to trigger this.
Without a reproducer, it's pretty much impossible to find out what
happened. Maybe AI could do it?
-- Steve
^ permalink raw reply
* Re: [PATCH mm-unstable v18 06/14] mm/khugepaged: generalize collapse_huge_page for mTHP collapse
From: Lance Yang @ 2026-06-02 16:34 UTC (permalink / raw)
To: npache
Cc: lance.yang, david, linux-doc, linux-kernel, linux-mm,
linux-trace-kernel, aarcange, akpm, anshuman.khandual, apopple,
baohua, baolin.wang, byungchul, catalin.marinas, cl, corbet,
dave.hansen, dev.jain, gourry, hannes, hughd, jack, jackmanb,
jannh, jglisse, joshua.hahnjy, kas, liam, ljs, mathieu.desnoyers,
matthew.brost, mhiramat, mhocko, peterx, pfalcato, rakie.kim,
raquini, rdunlap, richard.weiyang, rientjes, rostedt, rppt,
ryan.roberts, shivankg, sunnanyong, surenb, thomas.hellstrom,
tiwai, usamaarif642, vbabka, vishal.moola, wangkefeng.wang, will,
willy, yang, ying.huang, ziy, zokeefe, usama.arif
In-Reply-To: <CAA1CXcD7peS3WHueVgAWhhRrjBO_1b19+Xc0CfZBSO8OwJJKQw@mail.gmail.com>
On Tue, Jun 02, 2026 at 09:30:06AM -0600, Nico Pache wrote:
>On Mon, Jun 1, 2026 at 4:48 AM Lance Yang <lance.yang@linux.dev> wrote:
>>
>>
>>
>> On 2026/6/1 18:23, David Hildenbrand (Arm) wrote:
>> > On 6/1/26 11:08, Lance Yang wrote:
>> >>
>> >>
>> >> On 2026/6/1 14:54, David Hildenbrand (Arm) wrote:
>> >>> On 6/1/26 05:28, Lance Yang wrote:
>> >>>>
>> >>>>
>> >>>> Ah, fair point.
>> >>>>
>> >>>> I was mostly worried about arch hooks that walk vma->vm_mm again, rather
>> >>>> than only using the pte pointer passed in. For example, mips does:
>> >>>
>> >>> Right, a re-walk would be the real problem.
>> >>>
>> >>>>
>> >>>> update_mmu_cache_range()
>> >>>> -> __update_tlb()
>> >>>> -> pgd_offset(vma->vm_mm, address)
>> >>>> -> pte_offset_map(...)
>> >>>>
>> >>>> and __update_tlb() has this assumption:
>> >>>>
>> >>>> /*
>> >>>> * update_mmu_cache() is called between pte_offset_map_lock()
>> >>>> * and pte_unmap_unlock(), so we can assume that ptep is not
>> >>>> * NULL here: and what should be done below if it were NULL?
>> >>>> */
>> >>>>
>> >>>> So if khugepaged happens to run with current->active_mm == vma->vm_mm
>> >>>> here, could __update_tlb() hit the none PMD, get NULL from
>> >>>> pte_offset_map(), and then dereference it?
>> >>>
>> >>> Likely yes -- that MIPS code is horrible. And the comment in MIPS code
>> >>> even spells that out. :(
>> >>>
>> >>> Do you know about other code like that, or is MIPS the only one doing a
>> >>> re-walk and crossing fingers?
>> >>>
>> >>>>
>> >>>> Just wanted to raise it since some arch code may still have assumptions
>> >>>> like this, and the always-enable-mTHP work is getting closer ...
>> >>>
>> >>> Right. I assume set_pte_at() couldn't trigger something similar (re-walk) in
>> >>> arch code,
>> >>> because we simply provide the ptep. update_mmu_cache_range() only consumes the
>> >>> pte.
>> >>>
>> >>>>
>> >>>> Probably very very very hard to hit, though :)
>> >>>
>> >>> Delaying update_mmu_cache_range() is nasty, as we'd have to make sure that
>> >>> nobody can interfere in the meantime ... and the PMD lock will not be sufficient.
>> >>>
>> >>> Maybe we could reinstall the page table with the cleared (none) entries while
>> >>> still holding the PTL?
>> >>>
>> >>> Thinking out loud:
>> >>>
>> >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> >>> index 5ba298d420b7..e39b750b1e6f 100644
>> >>> --- a/mm/khugepaged.c
>> >>> +++ b/mm/khugepaged.c
>> >>> @@ -1413,13 +1413,17 @@ static enum scan_result collapse_huge_page(struct
>> >>> mm_struct *mm, unsigned long s
>> >>> map_anon_folio_pmd_nopf(folio, pmd, vma, pmd_addr);
>> >>> } else {
>> >>> /*
>> >>> - * set_ptes is called in map_anon_folio_pte_nopf with the
>> >>> - * pmd_ptl lock still held; this is safe as the PMD is expected
>> >>> - * to be none. The pmd entry is then repopulated below.
>> >>> + * Re-insert the page table with the cleared entries, but
>> >>> + * hold the PTL, such that no one can mess with the re-installed
>> >>> + * page table until we updated the temporarily-cleared entries
>> >>> + * through map_anon_folio_pte_nopf().
>> >>> */
>> >>> - map_anon_folio_pte_nopf(folio, pte, vma, start_addr, /
>> >>> *uffd_wp=*/ false);
>> >>> - smp_wmb(); /* make PTEs visible before PMD. See pmd_install() */
>> >>
>> >> One small thing, I think we should probably keep the smp_wmb(), and just
>> >> move it before the earlier pmd_populate().
>> >>
>> >> IIUC, the ordering we want is still:
>> >>
>> >> clear old PTEs
>> >> smp_wmb()
>> >> pmd_populate()
>> >>
>> >> so another CPU cannot walk through the re-installed PMD and still observe
>> >> the old PTEs, right?
>> >
>> > There is a smp_wmb() in __folio_mark_uptodate(), that should be sufficient?
>>
>> Ah, cool! __folio_mark_uptodate() already does the job :P
>>
>> So yeah, no extra smp_wmb() needed here!
>
>are we sure? that folio_mark_uptodate is done before the PTEs are
>reinstalled. Then we reinstall the PMD right after. Currently
>separated by the smp_wmb().
Reinstalling the PMD first makes the PTE table reachable again, right?
So before pmd_populate(), we only need to order the old PTE clears before
the PTE table is reachable again; __folio_mark_uptodate() already has the
smp_wmb() for that :)
The new PTEs are filled later under the PTL.
Hopefully I didn't miss soemthing :)
>I was copying this from other THP code that performs similar PTE/PMD juggling.
>
>I can remove it, but I'd rather air on the side of caution with this.
Cheers, Lance
^ permalink raw reply
* [PATCH 00/13] tracing/remotes: Add printk, dump_on_oops and boot parameters
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
This series extends the recently introduced trace remotes
infrastructure, bringing useful features for developers:
* dump_on_oops: Dump the trace remote buffer on system panic.
* printk: Redirect remote events to dmesg.
* trace_remote=: Configure a trace_remote from the commandline.
It also brings a couple of optimisations:
* Header compressed length support for small events.
* Single work thread for remote polling.
And some misc improvements:
* Use kstrtobool where possible
* Fix trace remote unregistering
I didn't put a "Fixes:" tag on the commit which is fixing the remote
registration because I do not believe this is something any user can
trigger.
Vincent Donnefort (13):
tracing/remotes: Release tracefs,eventfs on registration failure
tracing/remotes: Use kstrtobool for boolean tracefs files
tracing/remotes: Use a single per-remote polling work
tracing/simple_ring_buffer: Add support for compressed length
tracing/remotes: Add printk tracefs file
tracing/remotes: selftests: Add a test for the printk tracefs file
tracing/remotes: selftests: Prefix hypervisor folder
ring-buffer: Add ring_buffer_read_remote_meta_page()
tracing/remotes: Add dump_on_oops tracefs file
tracing/remotes: selftests: Add a test for the dump_on_oops tracefs
file
Documentation: tracing/remotes: Add detailed tracefs layout
tracing/remotes: Add trace_remote cmdline options
Documentation/kernel-parameters: Add trace_remote
.../admin-guide/kernel-parameters.txt | 16 +
Documentation/trace/remotes.rst | 63 +-
include/linux/ring_buffer.h | 1 +
kernel/trace/ring_buffer.c | 53 ++
kernel/trace/simple_ring_buffer.c | 22 +-
kernel/trace/trace_remote.c | 649 +++++++++++++++---
.../buffer_size.tc | 0
.../remotes/00hypervisor/dump_on_oops.tc | 11 +
.../{hypervisor => 00hypervisor}/hotplug.tc | 0
.../test.d/remotes/00hypervisor/printk.tc | 11 +
.../{hypervisor => 00hypervisor}/reset.tc | 0
.../{hypervisor => 00hypervisor}/trace.tc | 0
.../trace_pipe.tc | 0
.../{hypervisor => 00hypervisor}/unloading.tc | 0
.../ftrace/test.d/remotes/dump_on_oops.tc | 51 ++
.../selftests/ftrace/test.d/remotes/functions | 2 +
.../selftests/ftrace/test.d/remotes/printk.tc | 72 ++
17 files changed, 847 insertions(+), 104 deletions(-)
rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/buffer_size.tc (100%)
create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/dump_on_oops.tc
rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/hotplug.tc (100%)
create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/printk.tc
rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/reset.tc (100%)
rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/trace.tc (100%)
rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/trace_pipe.tc (100%)
rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/unloading.tc (100%)
create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/dump_on_oops.tc
create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/printk.tc
base-commit: e43ffb69e0438cddd72aaa30898b4dc446f664f8
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply
* [PATCH 01/13] tracing/remotes: Release tracefs,eventfs on registration failure
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
In trace_remote_register(), if registration of events or the init
callback fails, the created tracefs and eventfs directories are leaked.
Release the entire eventfs and tracefs hierarchy on trace_remote
registration.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index d6c3f94d67cd..cfe84e9b8fe6 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -44,7 +44,8 @@ struct trace_remote {
struct trace_buffer *trace_buffer;
struct trace_buffer_desc *trace_buffer_desc;
struct dentry *dentry;
- struct eventfs_inode *eventfs;
+ struct eventfs_inode *eventfs_root;
+ struct eventfs_inode *eventfs_subdir;
struct remote_event *events;
unsigned long nr_events;
unsigned long trace_buffer_size;
@@ -795,26 +796,28 @@ static const struct file_operations trace_fops = {
.release = trace_release,
};
+static struct dentry *tracefs_root;
+static DEFINE_MUTEX(tracefs_lock);
+static u64 tracefs_root_count;
+
static int trace_remote_init_tracefs(const char *name, struct trace_remote *remote)
{
struct dentry *remote_d, *percpu_d, *d;
- static struct dentry *root;
- static DEFINE_MUTEX(lock);
bool root_inited = false;
int cpu;
- guard(mutex)(&lock);
+ guard(mutex)(&tracefs_lock);
- if (!root) {
- root = tracefs_create_dir(TRACEFS_DIR, NULL);
- if (!root) {
+ if (!tracefs_root) {
+ tracefs_root = tracefs_create_dir(TRACEFS_DIR, NULL);
+ if (!tracefs_root) {
pr_err("Failed to create tracefs dir "TRACEFS_DIR"\n");
return -ENOMEM;
}
root_inited = true;
}
- remote_d = tracefs_create_dir(name, root);
+ remote_d = tracefs_create_dir(name, tracefs_root);
if (!remote_d) {
pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/\n", name);
goto err;
@@ -866,14 +869,15 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
goto err;
}
+ tracefs_root_count++;
remote->dentry = remote_d;
return 0;
err:
if (root_inited) {
- tracefs_remove(root);
- root = NULL;
+ tracefs_remove(tracefs_root);
+ tracefs_root = NULL;
} else {
tracefs_remove(remote_d);
}
@@ -881,8 +885,26 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
return -ENOMEM;
}
+static void trace_remote_remove_tracefs(struct trace_remote *remote)
+{
+ guard(mutex)(&tracefs_lock);
+
+ if (!remote->dentry)
+ return;
+
+ tracefs_remove(remote->dentry);
+ remote->dentry = NULL;
+
+ tracefs_root_count--;
+ if (!tracefs_root_count) {
+ tracefs_remove(tracefs_root);
+ tracefs_root = NULL;
+ }
+}
+
static int trace_remote_register_events(const char *remote_name, struct trace_remote *remote,
struct remote_event *events, size_t nr_events);
+static void trace_remote_unregister_events(struct trace_remote *remote);
/**
* trace_remote_register() - Register a Tracefs remote
@@ -905,10 +927,9 @@ static int trace_remote_register_events(const char *remote_name, struct trace_re
int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv,
struct remote_event *events, size_t nr_events)
{
- struct trace_remote *remote;
+ struct trace_remote *remote __free(kfree) = kzalloc_obj(*remote);
int ret;
- remote = kzalloc_obj(*remote);
if (!remote)
return -ENOMEM;
@@ -919,22 +940,30 @@ int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs,
mutex_init(&remote->lock);
init_rwsem(&remote->reader_lock);
- if (trace_remote_init_tracefs(name, remote)) {
- kfree(remote);
- return -ENOMEM;
- }
+ ret = trace_remote_init_tracefs(name, remote);
+ if (ret)
+ return ret;
ret = trace_remote_register_events(name, remote, events, nr_events);
if (ret) {
pr_err("Failed to register events for trace remote '%s' (%d)\n",
name, ret);
- return ret;
+ goto err_remove_tracefs;
}
ret = cbs->init ? cbs->init(remote->dentry, priv) : 0;
- if (ret)
+ if (ret) {
pr_err("Init failed for trace remote '%s' (%d)\n", name, ret);
+ goto err_unregister_events;
+ }
+
+ no_free_ptr(remote);
+ return 0;
+err_unregister_events:
+ trace_remote_unregister_events(remote);
+err_remove_tracefs:
+ trace_remote_remove_tracefs(remote);
return ret;
}
EXPORT_SYMBOL_GPL(trace_remote_register);
@@ -1267,7 +1296,6 @@ static int remote_events_dir_callback(const char *name, umode_t *mode, void **da
static int trace_remote_init_eventfs(const char *remote_name, struct trace_remote *remote,
struct remote_event *evt)
{
- struct eventfs_inode *eventfs = remote->eventfs;
static struct eventfs_entry dir_entries[] = {
{
.name = "enable",
@@ -1292,35 +1320,37 @@ static int trace_remote_init_eventfs(const char *remote_name, struct trace_remot
.callback = remote_event_callback,
}
};
- bool eventfs_create = false;
+ struct eventfs_inode *eventfs_root, *eventfs_subdir, *e;
- if (!eventfs) {
- eventfs = eventfs_create_events_dir("events", remote->dentry, dir_entries,
- ARRAY_SIZE(dir_entries), remote);
- if (IS_ERR(eventfs))
- return PTR_ERR(eventfs);
+ eventfs_root = remote->eventfs_root;
+ eventfs_subdir = remote->eventfs_subdir;
+ if (!eventfs_root) {
+ eventfs_root = eventfs_create_events_dir("events", remote->dentry, dir_entries,
+ ARRAY_SIZE(dir_entries), remote);
+ if (IS_ERR(eventfs_root))
+ return PTR_ERR(eventfs_root);
/*
* Create similar hierarchy as local events even if a single system is supported at
* the moment
*/
- eventfs = eventfs_create_dir(remote_name, eventfs, NULL, 0, NULL);
- if (IS_ERR(eventfs))
- return PTR_ERR(eventfs);
-
- remote->eventfs = eventfs;
- eventfs_create = true;
+ eventfs_subdir = eventfs_create_dir(remote_name, eventfs_root, NULL, 0, NULL);
+ if (IS_ERR(eventfs_subdir)) {
+ eventfs_remove_events_dir(eventfs_root);
+ return PTR_ERR(eventfs_subdir);
+ }
}
- eventfs = eventfs_create_dir(evt->name, eventfs, entries, ARRAY_SIZE(entries), evt);
- if (IS_ERR(eventfs)) {
- if (eventfs_create) {
- eventfs_remove_events_dir(remote->eventfs);
- remote->eventfs = NULL;
- }
- return PTR_ERR(eventfs);
+ e = eventfs_create_dir(evt->name, eventfs_subdir, entries, ARRAY_SIZE(entries), evt);
+ if (IS_ERR(e)) {
+ if (!remote->eventfs_root)
+ eventfs_remove_events_dir(eventfs_root);
+ return PTR_ERR(e);
}
+ remote->eventfs_root = eventfs_root;
+ remote->eventfs_subdir = eventfs_subdir;
+
return 0;
}
@@ -1335,11 +1365,11 @@ static int trace_remote_attach_events(struct trace_remote *remote, struct remote
if (evt->remote)
return -EEXIST;
- evt->remote = remote;
-
/* We need events to be sorted for efficient lookup */
if (i && evt->id <= events[i - 1].id)
return -EINVAL;
+
+ evt->remote = remote;
}
remote->events = events;
@@ -1348,14 +1378,33 @@ static int trace_remote_attach_events(struct trace_remote *remote, struct remote
return 0;
}
+static void trace_remote_detach_events(struct trace_remote *remote, struct remote_event *events,
+ size_t nr_events)
+{
+ int i;
+
+ for (i = 0; i < nr_events; i++) {
+ struct remote_event *evt = &events[i];
+
+ if (evt->remote == remote)
+ evt->remote = NULL;
+ }
+
+ remote->events = NULL;
+ remote->nr_events = 0;
+}
+
static int trace_remote_register_events(const char *remote_name, struct trace_remote *remote,
struct remote_event *events, size_t nr_events)
{
int i, ret;
ret = trace_remote_attach_events(remote, events, nr_events);
- if (ret)
+ if (ret) {
+ /* It is safe to call detach on a half-registered array */
+ trace_remote_detach_events(remote, events, nr_events);
return ret;
+ }
for (i = 0; i < nr_events; i++) {
struct remote_event *evt = &events[i];
@@ -1369,6 +1418,12 @@ static int trace_remote_register_events(const char *remote_name, struct trace_re
return 0;
}
+static void trace_remote_unregister_events(struct trace_remote *remote)
+{
+ trace_remote_detach_events(remote, remote->events, remote->nr_events);
+ eventfs_remove_events_dir(remote->eventfs_root);
+}
+
static int __cmp_events(const void *key, const void *data)
{
const struct remote_event *evt = data;
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
* [PATCH 02/13] tracing/remotes: Use kstrtobool for boolean tracefs files
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
Use kstrtobool in trace_remote.c where possible. This is more user-friendly
as it allows a better variety of input strings.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index cfe84e9b8fe6..7fed18f28fa7 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -176,10 +176,10 @@ tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t
{
struct seq_file *seq = filp->private_data;
struct trace_remote *remote = seq->private;
- unsigned long val;
+ bool val;
int ret;
- ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+ ret = kstrtobool_from_user(ubuf, cnt, &val);
if (ret)
return ret;
@@ -1090,10 +1090,10 @@ static ssize_t remote_event_enable_write(struct file *filp, const char __user *u
struct seq_file *seq = filp->private_data;
struct remote_event *evt = seq->private;
struct trace_remote *remote = evt->remote;
- u8 enable;
+ bool enable;
int ret;
- ret = kstrtou8_from_user(ubuf, count, 10, &enable);
+ ret = kstrtobool_from_user(ubuf, count, &enable);
if (ret)
return ret;
@@ -1174,10 +1174,10 @@ static ssize_t remote_events_dir_enable_write(struct file *filp, const char __us
size_t count, loff_t *ppos)
{
struct trace_remote *remote = file_inode(filp)->i_private;
+ bool enable;
int i, ret;
- u8 enable;
- ret = kstrtou8_from_user(ubuf, count, 10, &enable);
+ ret = kstrtobool_from_user(ubuf, count, &enable);
if (ret)
return ret;
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
* [PATCH 03/13] tracing/remotes: Use a single per-remote polling work
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
Having a per-iterator polling work is wasteful when logging several
trace_remote per_cpu/trace_pipe files in parallel. This result in one
work running per-CPU, where only one would suffice.
Transition to a single per-remote polling work, scheduled on the first
consumer creation and stopped when the last consuming iterator is freed.
This blanket polls all CPUs, regardless of which ones are actually being
read. This is acceptable because the poll consists of reading the
meta-page, which is a fast operation. Also, it is more common to log all
CPUs in the system than only one, so this use-case should be favoured.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 7fed18f28fa7..21583fae1bd9 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -26,7 +26,6 @@ enum tri_type {
struct trace_remote_iterator {
struct trace_remote *remote;
struct trace_seq seq;
- struct delayed_work poll_work;
unsigned long lost_events;
u64 ts;
struct ring_buffer_iter *rb_iter;
@@ -55,6 +54,8 @@ struct trace_remote {
struct rw_semaphore *pcpu_reader_locks;
unsigned int nr_readers;
unsigned int poll_ms;
+ struct delayed_work poll_work;
+ unsigned int poll_cnt;
bool tracing_on;
};
@@ -291,17 +292,6 @@ static bool trace_remote_has_cpu(struct trace_remote *remote, int cpu)
return ring_buffer_poll_remote(remote->trace_buffer, cpu) == 0;
}
-static void __poll_remote(struct work_struct *work)
-{
- struct delayed_work *dwork = to_delayed_work(work);
- struct trace_remote_iterator *iter;
-
- iter = container_of(dwork, struct trace_remote_iterator, poll_work);
- ring_buffer_poll_remote(iter->remote->trace_buffer, iter->cpu);
- schedule_delayed_work((struct delayed_work *)work,
- msecs_to_jiffies(iter->remote->poll_ms));
-}
-
static void __free_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu)
{
if (cpu != RING_BUFFER_ALL_CPUS) {
@@ -345,6 +335,36 @@ static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu)
return 0;
}
+static void __poll_remote(struct work_struct *work)
+{
+ struct delayed_work *dwork = to_delayed_work(work);
+ struct trace_remote *remote;
+
+ remote = container_of(dwork, struct trace_remote, poll_work);
+ ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS);
+
+ schedule_delayed_work(dwork, msecs_to_jiffies(remote->poll_ms));
+}
+
+static void trace_remote_inc_poll(struct trace_remote *remote)
+{
+ /* poll_cnt <= nr_readers, inherits its overflow protection */
+ if (!remote->poll_cnt++) {
+ ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS);
+ schedule_delayed_work(&remote->poll_work, msecs_to_jiffies(remote->poll_ms));
+ }
+}
+
+static void trace_remote_dec_poll(struct trace_remote *remote)
+{
+ if (WARN_ON_ONCE(!remote->poll_cnt))
+ return;
+
+ remote->poll_cnt--;
+ if (!remote->poll_cnt)
+ cancel_delayed_work_sync(&remote->poll_work);
+}
+
static struct trace_remote_iterator
*trace_remote_iter(struct trace_remote *remote, int cpu, enum tri_type type)
{
@@ -374,9 +394,7 @@ static struct trace_remote_iterator
switch (type) {
case TRI_CONSUMING:
- ring_buffer_poll_remote(remote->trace_buffer, cpu);
- INIT_DELAYED_WORK(&iter->poll_work, __poll_remote);
- schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_ms));
+ trace_remote_inc_poll(remote);
break;
case TRI_NONCONSUMING:
ret = __alloc_ring_buffer_iter(iter, cpu);
@@ -410,7 +428,7 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter)
switch (iter->type) {
case TRI_CONSUMING:
- cancel_delayed_work_sync(&iter->poll_work);
+ trace_remote_dec_poll(remote);
break;
case TRI_NONCONSUMING:
__free_ring_buffer_iter(iter, iter->cpu);
@@ -939,6 +957,7 @@ int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs,
remote->poll_ms = 100;
mutex_init(&remote->lock);
init_rwsem(&remote->reader_lock);
+ INIT_DELAYED_WORK(&remote->poll_work, __poll_remote);
ret = trace_remote_init_tracefs(name, remote);
if (ret)
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
* [PATCH 04/13] tracing/simple_ring_buffer: Add support for compressed length
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
The array length is the total size in bytes of the data for the current
event. It is possible to compress this value into the event header type,
which has 28 unused types, saving 32 bits for sufficiently small events.
The compressed length is expressed as a multiple of the ring-buffer
alignment, 4-bytes by default. Enforces this alignment.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c
index f4642f5adda3..6be4aa19adca 100644
--- a/kernel/trace/simple_ring_buffer.c
+++ b/kernel/trace/simple_ring_buffer.c
@@ -207,7 +207,12 @@ static unsigned long rb_event_size(unsigned long length)
{
struct ring_buffer_event *event;
- return length + RB_EVNT_HDR_SIZE + sizeof(event->array[0]);
+ length = ALIGN(length, RB_ALIGNMENT);
+
+ if (length > RB_MAX_SMALL_DATA)
+ length += sizeof(event->array[0]);
+
+ return length + RB_EVNT_HDR_SIZE;
}
static struct ring_buffer_event *
@@ -223,12 +228,15 @@ rb_event_add_ts_extend(struct ring_buffer_event *event, u64 delta)
static struct ring_buffer_event *
simple_rb_reserve_next(struct simple_rb_per_cpu *cpu_buffer, unsigned long length, u64 timestamp)
{
- unsigned long ts_ext_size = 0, event_size = rb_event_size(length);
struct simple_buffer_page *tail = cpu_buffer->tail_page;
+ unsigned long event_size, array_size, ts_ext_size = 0;
struct ring_buffer_event *event;
u32 write, prev_write;
u64 time_delta;
+ event_size = rb_event_size(length);
+ array_size = event_size - RB_EVNT_HDR_SIZE;
+
time_delta = timestamp - cpu_buffer->write_stamp;
if (test_time_stamp(time_delta))
@@ -259,9 +267,13 @@ simple_rb_reserve_next(struct simple_rb_per_cpu *cpu_buffer, unsigned long lengt
time_delta = 0;
}
- event->type_len = 0;
+ if (length > RB_MAX_SMALL_DATA) {
+ event->type_len = 0;
+ event->array[0] = array_size;
+ } else {
+ event->type_len = DIV_ROUND_UP(array_size, RB_ALIGNMENT);
+ }
event->time_delta = time_delta;
- event->array[0] = event_size - RB_EVNT_HDR_SIZE;
return event;
}
@@ -284,7 +296,7 @@ void *simple_ring_buffer_reserve(struct simple_rb_per_cpu *cpu_buffer, unsigned
rb_event = simple_rb_reserve_next(cpu_buffer, length, timestamp);
- return &rb_event->array[1];
+ return rb_event->type_len ? &rb_event->array[0] : &rb_event->array[1];
}
EXPORT_SYMBOL_GPL(simple_ring_buffer_reserve);
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
* [PATCH 05/13] tracing/remotes: Add printk tracefs file
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
When enabled, the printk tracefs file enables the redirection of all
events to dmesg. This is similar to tp_printk.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 21583fae1bd9..1bf0ba159c92 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -21,6 +21,7 @@
enum tri_type {
TRI_CONSUMING,
TRI_NONCONSUMING,
+ TRI_PRINTK,
};
struct trace_remote_iterator {
@@ -42,6 +43,7 @@ struct trace_remote {
void *priv;
struct trace_buffer *trace_buffer;
struct trace_buffer_desc *trace_buffer_desc;
+ struct trace_remote_iterator *printk;
struct dentry *dentry;
struct eventfs_inode *eventfs_root;
struct eventfs_inode *eventfs_subdir;
@@ -335,6 +337,8 @@ static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu)
return 0;
}
+static void trace_remote_do_printk(struct trace_remote *remote);
+
static void __poll_remote(struct work_struct *work)
{
struct delayed_work *dwork = to_delayed_work(work);
@@ -342,6 +346,7 @@ static void __poll_remote(struct work_struct *work)
remote = container_of(dwork, struct trace_remote, poll_work);
ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS);
+ trace_remote_do_printk(remote);
schedule_delayed_work(dwork, msecs_to_jiffies(remote->poll_ms));
}
@@ -351,6 +356,8 @@ static void trace_remote_inc_poll(struct trace_remote *remote)
/* poll_cnt <= nr_readers, inherits its overflow protection */
if (!remote->poll_cnt++) {
ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS);
+ trace_remote_do_printk(remote);
+
schedule_delayed_work(&remote->poll_work, msecs_to_jiffies(remote->poll_ms));
}
}
@@ -393,6 +400,14 @@ static struct trace_remote_iterator
trace_seq_init(&iter->seq);
switch (type) {
+ case TRI_PRINTK:
+ /* only one printk iter allowed */
+ if (WARN_ON_ONCE(remote->printk)) {
+ ret = -EBUSY;
+ break;
+ }
+ smp_store_release(&remote->printk, iter);
+ fallthrough;
case TRI_CONSUMING:
trace_remote_inc_poll(remote);
break;
@@ -427,6 +442,11 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter)
lockdep_assert_held(&remote->lock);
switch (iter->type) {
+ case TRI_PRINTK:
+ WARN_ON_ONCE(remote->printk != iter);
+ smp_store_release(&remote->printk, NULL);
+ flush_delayed_work(&remote->poll_work);
+ fallthrough;
case TRI_CONSUMING:
trace_remote_dec_poll(remote);
break;
@@ -504,6 +524,7 @@ __peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long
struct ring_buffer_iter *rb_iter;
switch (iter->type) {
+ case TRI_PRINTK:
case TRI_CONSUMING:
return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events);
case TRI_NONCONSUMING:
@@ -571,6 +592,7 @@ static void trace_remote_iter_move(struct trace_remote_iterator *iter)
struct trace_buffer *trace_buffer = iter->remote->trace_buffer;
switch (iter->type) {
+ case TRI_PRINTK:
case TRI_CONSUMING:
ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL);
break;
@@ -814,6 +836,80 @@ static const struct file_operations trace_fops = {
.release = trace_release,
};
+static void trace_remote_do_printk(struct trace_remote *remote)
+{
+ struct trace_remote_iterator *iter = smp_load_acquire(&remote->printk);
+
+ if (!iter)
+ return;
+
+ trace_remote_iter_read_start(iter);
+
+ while (trace_remote_iter_read_event(iter)) {
+ trace_seq_init(&iter->seq);
+
+ trace_remote_iter_print_event(iter);
+ if (!pr_emerg("%s", iter->seq.buffer))
+ break;
+
+ trace_remote_iter_move(iter);
+ }
+
+ trace_remote_iter_read_finished(iter);
+}
+
+static int trace_remote_enable_printk(struct trace_remote *remote, bool enable)
+{
+ struct trace_remote_iterator *iter = remote->printk;
+
+ lockdep_assert_held(&remote->lock);
+
+ if (enable == !!iter)
+ return 0;
+
+ if (enable) {
+ iter = trace_remote_iter(remote, RING_BUFFER_ALL_CPUS, TRI_PRINTK);
+ if (IS_ERR(iter))
+ return PTR_ERR(iter);
+ } else {
+ trace_remote_iter_free(remote->printk);
+ /* trace_remote_iter_free has reset remote->printk */
+ }
+
+ return 0;
+}
+
+static ssize_t
+printk_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+ struct seq_file *seq = filp->private_data;
+ struct trace_remote *remote = seq->private;
+ bool val;
+ int ret;
+
+ ret = kstrtobool_from_user(ubuf, cnt, &val);
+ if (ret)
+ return ret;
+
+ guard(mutex)(&remote->lock);
+
+ ret = trace_remote_enable_printk(remote, val);
+ if (ret)
+ return ret;
+
+ return cnt;
+}
+
+static int printk_show(struct seq_file *s, void *unused)
+{
+ struct trace_remote *remote = s->private;
+
+ seq_printf(s, "%d\n", !!remote->printk);
+
+ return 0;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(printk);
+
static struct dentry *tracefs_root;
static DEFINE_MUTEX(tracefs_lock);
static u64 tracefs_root_count;
@@ -858,6 +954,10 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
if (!d)
goto err;
+ d = trace_create_file("printk", TRACEFS_MODE_WRITE, remote_d, remote, &printk_fops);
+ if (!d)
+ goto err;
+
percpu_d = tracefs_create_dir("per_cpu", remote_d);
if (!percpu_d) {
pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/per_cpu/\n", name);
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
* [PATCH 06/13] tracing/remotes: selftests: Add a test for the printk tracefs file
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
Exercise the newly introduced printk tracefs file that turns on and off
the dmesg redirection.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/functions b/tools/testing/selftests/ftrace/test.d/remotes/functions
index 05224fac3653..8dd9c961977b 100644
--- a/tools/testing/selftests/ftrace/test.d/remotes/functions
+++ b/tools/testing/selftests/ftrace/test.d/remotes/functions
@@ -8,6 +8,7 @@ setup_remote()
cd remotes/$name/
echo 0 > tracing_on
+ echo 0 > printk
clear_trace
echo 7 > buffer_size_kb
echo 0 > events/enable
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/printk.tc b/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/printk.tc
new file mode 100644
index 000000000000..aca7a2bfe293
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/printk.tc
@@ -0,0 +1,11 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote printk, the dmesg redirection
+# requires: remotes/hypervisor/write_event
+
+SOURCE_REMOTE_TEST=1
+. $TEST_DIR/remotes/printk.tc
+
+set -e
+setup_remote "hypervisor"
+test_printk
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/printk.tc b/tools/testing/selftests/ftrace/test.d/remotes/printk.tc
new file mode 100644
index 000000000000..80eaf13e240d
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/printk.tc
@@ -0,0 +1,72 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote printk, the dmesg redirection
+# requires: remotes/test
+
+. $TEST_DIR/remotes/functions
+
+test_printk()
+{
+ echo 0 > tracing_on
+ assert_unloaded
+
+ #
+ # Test printk on/off when tracing is disabled
+ #
+ echo 1 > printk
+ test $(cat printk) -eq 1
+ assert_loaded
+
+ echo 0 > printk
+ test $(cat printk) -eq 0
+ assert_unloaded
+
+ #
+ # Test events are logged to dmesg
+ #
+ dmesg -c > /dev/null
+
+ echo 1 > tracing_on
+ assert_loaded
+ echo 1 > printk
+ test $(cat printk) -eq 1
+
+ nr_events=128
+ for i in $(seq 1 $nr_events); do
+ echo $i > write_event
+ done
+
+ sleep 1
+ output=$(mktemp $TMPDIR/remote_test.XXXXXX)
+ dmesg | grep "selftest id=" | sed 's/^[^]]*] //'> $output
+
+ check_trace 1 $nr_events $output
+
+ rm $output
+
+ #
+ # Disable printk and Test events were not consumed by dmesg
+ #
+ echo 0 > printk
+ test $(cat printk) -eq 0
+
+ start_id=$(($nr_events + 1))
+ end_id=$(($start_id + $nr_events))
+
+ for i in $(seq $start_id $end_id); do
+ echo $i > write_event
+ done
+
+ sleep 1
+
+ output=$(dump_trace_pipe)
+ check_trace $start_id $end_id $output
+ rm $output
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+ set -e
+
+ setup_remote_test
+ test_printk
+fi
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
* [PATCH 07/13] tracing/remotes: selftests: Prefix hypervisor folder
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
Avoid interleaving run tests by prefixing the hypervisor folder.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/buffer_size.tc b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/buffer_size.tc
similarity index 100%
rename from tools/testing/selftests/ftrace/test.d/remotes/hypervisor/buffer_size.tc
rename to tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/buffer_size.tc
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/hotplug.tc b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/hotplug.tc
similarity index 100%
rename from tools/testing/selftests/ftrace/test.d/remotes/hypervisor/hotplug.tc
rename to tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/hotplug.tc
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/printk.tc b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/printk.tc
similarity index 100%
rename from tools/testing/selftests/ftrace/test.d/remotes/hypervisor/printk.tc
rename to tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/printk.tc
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/reset.tc b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/reset.tc
similarity index 100%
rename from tools/testing/selftests/ftrace/test.d/remotes/hypervisor/reset.tc
rename to tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/reset.tc
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/trace.tc b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/trace.tc
similarity index 100%
rename from tools/testing/selftests/ftrace/test.d/remotes/hypervisor/trace.tc
rename to tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/trace.tc
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/trace_pipe.tc b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/trace_pipe.tc
similarity index 100%
rename from tools/testing/selftests/ftrace/test.d/remotes/hypervisor/trace_pipe.tc
rename to tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/trace_pipe.tc
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/hypervisor/unloading.tc b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/unloading.tc
similarity index 100%
rename from tools/testing/selftests/ftrace/test.d/remotes/hypervisor/unloading.tc
rename to tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/unloading.tc
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply
* [PATCH 08/13] ring-buffer: Add ring_buffer_read_remote_meta_page()
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
In preparation for the introduction of a panic handler for trace
remotes, add a ring_buffer_read_remote_meta_page(). This is basically
similar to ring_buffer_poll_remote, but it doesn't try to wake-up
readers and, in the !RING_BUFFER_ALL_CPUS case, uses panic-friendly
locks.
While at it, update trace_remote_has_cpu() to use this new function
instead of ring_buffer_poll_remote(), avoiding unnecessary wakeups when
verifying if a CPU buffer is active.
Finally, the distracted engineer who wrote that
ring_buffer_poll_remote() forgot to document it. Add a kerneldoc for
that function too.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 994f52b34344..6e008a548063 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -298,6 +298,7 @@ struct ring_buffer_remote {
void *priv;
};
+int ring_buffer_read_remote_meta_page(struct trace_buffer *buffer, int cpu);
int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu);
struct trace_buffer *
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 7b07d2004cc6..88ac346c65ec 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -6623,6 +6623,59 @@ bool ring_buffer_empty_cpu(struct trace_buffer *buffer, int cpu)
}
EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
+/**
+ * ring_buffer_read_remote_meta_page - read the meta page of a remote ring buffer
+ * @buffer: The ring buffer
+ * @cpu: The CPU buffer to read (or RING_BUFFER_ALL_CPUS)
+ *
+ * Returns:
+ * 0 on success, or -EINVAL if the CPU is not in the buffer's cpumask.
+ */
+int ring_buffer_read_remote_meta_page(struct trace_buffer *buffer, int cpu)
+{
+ struct ring_buffer_per_cpu *cpu_buffer;
+
+ if (cpu != RING_BUFFER_ALL_CPUS) {
+ unsigned long flags;
+ bool dolock;
+
+ if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ return -EINVAL;
+
+ cpu_buffer = buffer->buffers[cpu];
+
+ local_irq_save(flags);
+ dolock = rb_reader_lock(cpu_buffer);
+ rb_read_remote_meta_page(cpu_buffer);
+ rb_reader_unlock(cpu_buffer, dolock);
+ local_irq_restore(flags);
+ return 0;
+ }
+
+ guard(cpus_read_lock)();
+
+ for_each_buffer_cpu(buffer, cpu) {
+ cpu_buffer = buffer->buffers[cpu];
+
+ guard(raw_spinlock)(&cpu_buffer->reader_lock);
+ rb_read_remote_meta_page(cpu_buffer);
+ }
+
+ return 0;
+}
+
+/**
+ * ring_buffer_poll_remote - poll a remote ring buffer for new data
+ * @buffer: The ring buffer
+ * @cpu: The CPU buffer to poll (or RING_BUFFER_ALL_CPUS)
+ *
+ * This function polls the specified remote CPU buffer (or all of them)
+ * by reading its meta page to update the local reader's view. If new
+ * entries are detected, it triggers wakeups for any waiting readers.
+ *
+ * Returns:
+ * 0 on success, or -EINVAL if the CPU is not in the buffer's cpumask.
+ */
int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 1bf0ba159c92..e708dcd7d258 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -291,7 +291,7 @@ static bool trace_remote_has_cpu(struct trace_remote *remote, int cpu)
if (cpu == RING_BUFFER_ALL_CPUS)
return true;
- return ring_buffer_poll_remote(remote->trace_buffer, cpu) == 0;
+ return ring_buffer_read_remote_meta_page(remote->trace_buffer, cpu) == 0;
}
static void __free_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu)
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
* [PATCH 09/13] tracing/remotes: Add dump_on_oops tracefs file
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
When enabled, dump_on_oops will dump the content of the trace remote
buffer if the system panics.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index e708dcd7d258..3164f327d4d8 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -7,6 +7,7 @@
#include <linux/kstrtox.h>
#include <linux/lockdep.h>
#include <linux/mutex.h>
+#include <linux/panic_notifier.h>
#include <linux/tracefs.h>
#include <linux/trace_remote.h>
#include <linux/trace_seq.h>
@@ -22,6 +23,7 @@ enum tri_type {
TRI_CONSUMING,
TRI_NONCONSUMING,
TRI_PRINTK,
+ TRI_PANIC,
};
struct trace_remote_iterator {
@@ -58,6 +60,9 @@ struct trace_remote {
unsigned int poll_ms;
struct delayed_work poll_work;
unsigned int poll_cnt;
+ struct notifier_block panic_notifier;
+ struct trace_remote_iterator *panic_iter;
+ bool panic_on;
bool tracing_on;
};
@@ -66,10 +71,15 @@ static bool trace_remote_loaded(struct trace_remote *remote)
return !!remote->trace_buffer;
}
+static void trace_remote_unload(struct trace_remote *remote);
+static int trace_remote_panic_load(struct trace_remote *remote);
+static void trace_remote_panic_unload(struct trace_remote *remote);
+
static int trace_remote_load(struct trace_remote *remote)
{
struct ring_buffer_remote *rb_remote = &remote->rb_remote;
struct trace_buffer_desc *desc;
+ int ret = 0;
lockdep_assert_held(&remote->lock);
@@ -84,15 +94,28 @@ static int trace_remote_load(struct trace_remote *remote)
rb_remote->swap_reader_page = remote->cbs->swap_reader_page;
rb_remote->priv = remote->priv;
rb_remote->reset = remote->cbs->reset;
+ remote->trace_buffer_desc = desc;
remote->trace_buffer = ring_buffer_alloc_remote(rb_remote);
if (!remote->trace_buffer) {
remote->cbs->unload_trace_buffer(desc, remote->priv);
return -ENOMEM;
}
- remote->trace_buffer_desc = desc;
+ if (remote->panic_on) {
+ ret = trace_remote_panic_load(remote);
+ if (ret)
+ trace_remote_unload(remote);
+ }
- return 0;
+ return ret;
+}
+
+static void trace_remote_unload(struct trace_remote *remote)
+{
+ trace_remote_panic_unload(remote);
+ ring_buffer_free(remote->trace_buffer);
+ remote->trace_buffer = NULL;
+ remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv);
}
static void trace_remote_try_unload(struct trace_remote *remote)
@@ -110,9 +133,7 @@ static void trace_remote_try_unload(struct trace_remote *remote)
if (!ring_buffer_empty(remote->trace_buffer))
return;
- ring_buffer_free(remote->trace_buffer);
- remote->trace_buffer = NULL;
- remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv);
+ trace_remote_unload(remote);
}
static int trace_remote_enable_tracing(struct trace_remote *remote)
@@ -375,58 +396,68 @@ static void trace_remote_dec_poll(struct trace_remote *remote)
static struct trace_remote_iterator
*trace_remote_iter(struct trace_remote *remote, int cpu, enum tri_type type)
{
- struct trace_remote_iterator *iter = NULL;
+ struct trace_remote_iterator *iter __free(kfree) = kzalloc_obj(*iter);
int ret;
lockdep_assert_held(&remote->lock);
- if (type == TRI_NONCONSUMING && !trace_remote_loaded(remote))
- return NULL;
+ if (!iter)
+ return ERR_PTR(-ENOMEM);
- ret = trace_remote_get(remote, cpu);
- if (ret)
- return ERR_PTR(ret);
+ switch (type) {
+ case TRI_NONCONSUMING:
+ if (!trace_remote_loaded(remote))
+ return NULL;
+ fallthrough;
+ case TRI_CONSUMING:
+ case TRI_PRINTK:
+ ret = trace_remote_get(remote, cpu);
+ if (ret)
+ return ERR_PTR(ret);
+ break;
+ case TRI_PANIC:
+ break;
+ }
if (!trace_remote_has_cpu(remote, cpu)) {
ret = -ENODEV;
goto err;
}
- iter = kzalloc_obj(*iter);
- if (iter) {
- iter->remote = remote;
- iter->cpu = cpu;
- iter->type = type;
- trace_seq_init(&iter->seq);
+ iter->remote = remote;
+ iter->cpu = cpu;
+ iter->type = type;
+ trace_seq_init(&iter->seq);
- switch (type) {
- case TRI_PRINTK:
- /* only one printk iter allowed */
- if (WARN_ON_ONCE(remote->printk)) {
- ret = -EBUSY;
- break;
- }
- smp_store_release(&remote->printk, iter);
- fallthrough;
- case TRI_CONSUMING:
- trace_remote_inc_poll(remote);
- break;
- case TRI_NONCONSUMING:
- ret = __alloc_ring_buffer_iter(iter, cpu);
- break;
+ switch (type) {
+ case TRI_PRINTK:
+ /* only one printk iter allowed */
+ if (WARN_ON_ONCE(remote->printk)) {
+ ret = -EBUSY;
+ goto err;
}
-
+ smp_store_release(&remote->printk, iter);
+ fallthrough;
+ case TRI_CONSUMING:
+ trace_remote_inc_poll(remote);
+ break;
+ case TRI_PANIC:
+ case TRI_NONCONSUMING:
+ ret = __alloc_ring_buffer_iter(iter, cpu);
if (ret)
goto err;
-
- return iter;
+ break;
}
- ret = -ENOMEM;
-err:
- kfree(iter);
- trace_remote_put(remote);
+ return no_free_ptr(iter);
+err:
+ switch (type) {
+ case TRI_PANIC:
+ break;
+ default:
+ trace_remote_put(remote);
+ }
return ERR_PTR(ret);
}
@@ -449,14 +480,18 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter)
fallthrough;
case TRI_CONSUMING:
trace_remote_dec_poll(remote);
+ trace_remote_put(remote);
break;
case TRI_NONCONSUMING:
+ trace_remote_put(remote);
+ __free_ring_buffer_iter(iter, iter->cpu);
+ break;
+ case TRI_PANIC:
__free_ring_buffer_iter(iter, iter->cpu);
break;
}
kfree(iter);
- trace_remote_put(remote);
}
static void trace_remote_iter_read_start(struct trace_remote_iterator *iter)
@@ -527,6 +562,7 @@ __peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long
case TRI_PRINTK:
case TRI_CONSUMING:
return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events);
+ case TRI_PANIC:
case TRI_NONCONSUMING:
rb_iter = __get_rb_iter(iter, cpu);
if (!rb_iter)
@@ -596,6 +632,7 @@ static void trace_remote_iter_move(struct trace_remote_iterator *iter)
case TRI_CONSUMING:
ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL);
break;
+ case TRI_PANIC:
case TRI_NONCONSUMING:
ring_buffer_iter_advance(__get_rb_iter(iter, iter->evt_cpu));
break;
@@ -910,6 +947,116 @@ static int printk_show(struct seq_file *s, void *unused)
}
DEFINE_SHOW_STORE_ATTRIBUTE(printk);
+static int trace_remote_panic_handler(struct notifier_block *self, unsigned long ev, void *v)
+{
+ struct trace_remote *remote = container_of(self, struct trace_remote, panic_notifier);
+ struct trace_remote_iterator *iter = smp_load_acquire(&remote->panic_iter);
+ int cpu;
+
+ if (!iter) {
+ pr_warn("Unexpected error: no panic iterator for the trace remote\n");
+ return NOTIFY_DONE;
+ }
+
+ for_each_possible_cpu(cpu) {
+ if (iter->rb_iters[cpu]) {
+ /* No RING_BUFFER_ALL_CPUS to avoid taking cpu_read_lock() */
+ ring_buffer_read_remote_meta_page(remote->trace_buffer, cpu);
+ ring_buffer_iter_reset(iter->rb_iters[cpu]);
+ }
+ }
+
+ while (trace_remote_iter_read_event(iter)) {
+ trace_seq_init(&iter->seq);
+
+ trace_remote_iter_print_event(iter);
+ pr_emerg("%s", iter->seq.buffer);
+
+ trace_remote_iter_move(iter);
+ }
+
+ return NOTIFY_DONE;
+}
+
+static int trace_remote_panic_load(struct trace_remote *remote)
+{
+ struct notifier_block *notifier = &remote->panic_notifier;
+ struct trace_remote_iterator *iter;
+
+ lockdep_assert_held(&remote->lock);
+
+ if (remote->panic_iter)
+ return 0;
+
+ iter = trace_remote_iter(remote, RING_BUFFER_ALL_CPUS, TRI_PANIC);
+ if (IS_ERR(iter))
+ return PTR_ERR(iter);
+
+ smp_store_release(&remote->panic_iter, iter);
+
+ notifier->notifier_call = trace_remote_panic_handler;
+ notifier->priority = INT_MAX - 1;
+ atomic_notifier_chain_register(&panic_notifier_list, notifier);
+
+ return 0;
+}
+
+static void trace_remote_panic_unload(struct trace_remote *remote)
+{
+ struct trace_remote_iterator *iter = remote->panic_iter;
+
+ lockdep_assert_held(&remote->lock);
+
+ if (!iter)
+ return;
+
+ atomic_notifier_chain_unregister(&panic_notifier_list, &remote->panic_notifier);
+ smp_store_release(&remote->panic_iter, NULL);
+ trace_remote_iter_free(iter);
+}
+
+static ssize_t dump_on_oops_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ struct seq_file *seq = filp->private_data;
+ struct trace_remote *remote = seq->private;
+ bool enable;
+ int ret;
+
+ ret = kstrtobool_from_user(ubuf, cnt, &enable);
+ if (ret)
+ return ret;
+
+ guard(mutex)(&remote->lock);
+
+ if (enable == remote->panic_on)
+ return cnt;
+
+ if (trace_remote_loaded(remote)) {
+ if (enable) {
+ ret = trace_remote_panic_load(remote);
+ if (ret)
+ return ret;
+ } else {
+ trace_remote_panic_unload(remote);
+ }
+ }
+
+ remote->panic_on = enable;
+
+ return cnt;
+}
+
+static int dump_on_oops_show(struct seq_file *s, void *unused)
+{
+ struct trace_remote *remote = s->private;
+
+ seq_printf(s, "%d\n", remote->panic_on);
+
+ return 0;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(dump_on_oops);
+
static struct dentry *tracefs_root;
static DEFINE_MUTEX(tracefs_lock);
static u64 tracefs_root_count;
@@ -941,6 +1088,11 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
if (!d)
goto err;
+ d = trace_create_file("dump_on_oops", TRACEFS_MODE_WRITE, remote_d, remote,
+ &dump_on_oops_fops);
+ if (!d)
+ goto err;
+
d = trace_create_file("buffer_size_kb", TRACEFS_MODE_WRITE, remote_d, remote,
&buffer_size_kb_fops);
if (!d)
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
* [PATCH 10/13] tracing/remotes: selftests: Add a test for the dump_on_oops tracefs file
From: Vincent Donnefort @ 2026-06-02 17:11 UTC (permalink / raw)
To: rostedt, mhiramat, mathieu.desnoyers, linux-trace-kernel
Cc: kernel-team, linux-kernel, Vincent Donnefort
In-Reply-To: <20260602171146.2238998-1-vdonnefort@google.com>
Exercise the newly introduced dump_on_oops tracefs file that turns on
or off the trace remote buffer dump on system panic.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/dump_on_oops.tc b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/dump_on_oops.tc
new file mode 100644
index 000000000000..6c3f93ab922d
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/dump_on_oops.tc
@@ -0,0 +1,11 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test hypervisor trace dump_on_oops
+# requires: remotes/hypervisor/write_event
+
+SOURCE_REMOTE_TEST=1
+. $TEST_DIR/remotes/dump_on_oops.tc
+
+set -e
+setup_remote "hypervisor"
+test_dump_on_oops
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/dump_on_oops.tc b/tools/testing/selftests/ftrace/test.d/remotes/dump_on_oops.tc
new file mode 100644
index 000000000000..4f5f26cb3291
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/dump_on_oops.tc
@@ -0,0 +1,51 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote dump_on_oops
+# requires: remotes/test
+
+. $TEST_DIR/remotes/functions
+
+test_dump_on_oops()
+{
+ #
+ # Toggle when the buffer is unloaded
+ #
+ echo 1 > dump_on_oops
+ echo 0 > dump_on_oops
+
+ #
+ # Toggle when the buffer is loaded
+ #
+ echo 1 > tracing_on
+ assert_loaded
+
+ echo 1 > dump_on_oops
+ echo 0 > dump_on_oops
+
+ #
+ # Load and unload buffer while dump_on_oops is enabled
+ #
+ echo 0 > tracing_on
+ assert_unloaded
+
+ echo 1 > dump_on_oops
+ echo 1 > tracing_on
+ echo 0 > tracing_on
+
+ # REMOVE ME FOR A PROPER OOPS TEST
+ return
+
+ echo 1 > tracing_on
+
+ for i in $(seq 1 32); do
+ echo $i > write_event
+ done
+
+ echo c > /proc/sysrq-trigger
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+ set -e
+ setup_remote_test
+ test_dump_on_oops
+fi
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/functions b/tools/testing/selftests/ftrace/test.d/remotes/functions
index 8dd9c961977b..887b9296d0a7 100644
--- a/tools/testing/selftests/ftrace/test.d/remotes/functions
+++ b/tools/testing/selftests/ftrace/test.d/remotes/functions
@@ -9,6 +9,7 @@ setup_remote()
cd remotes/$name/
echo 0 > tracing_on
echo 0 > printk
+ echo 0 > dump_on_oops
clear_trace
echo 7 > buffer_size_kb
echo 0 > events/enable
--
2.54.0.1032.g2f8565e1d1-goog
^ permalink raw reply related
page: next (older) | prev (newer) | latest
- recent:[subjects (threaded)|topics (new)|topics (active)]
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox