* + mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch added to mm-hotfixes-unstable branch
@ 2026-04-28 12:59 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-04-28 12:59 UTC (permalink / raw)
To: mm-commits, shakeel.butt, roman.gushchin, muchun.song, mhocko,
hannes, zhengqi.arch, akpm
The patch titled
Subject: mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Qi Zheng <zhengqi.arch@bytedance.com>
Subject: mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end()
Date: Tue, 28 Apr 2026 18:31:08 +0800
Currently, get_non_dying_memcg_start() and get_non_dying_memcg_end() both
evaluate cgroup_subsys_on_dfl(memory_cgrp_subsys) independently to
determine whether to acquire or release the RCU read lock.
However, the result of cgroup_subsys_on_dfl() can change dynamically at
runtime due to cgroup hierarchy rebinding (e.g., when the memory
controller is moved between cgroup v1 and v2 hierarchies). This can cause
the following warning:
=====================================
WARNING: bad unlock balance detected!
7.0.0-next-20260420+ #83 Tainted: G W
-------------------------------------
memcg-repro/270 is trying to release lock (rcu_read_lock) at:
[<ffffffff815f57f7>] rcu_read_unlock+0x17/0x60
but there are no more locks to release!
other info that might help us debug this:
1 lock held by memcg-repro/270:
#0: ffff888102fa2088 (vm_lock){++++}-{0:0}, at: do_user_addr_fault+0x285/0x880
stack backtrace:
CPU: 0 UID: 0 PID: 270 Comm: memcg-repro Tainted: G W 7.0.0-next-20260420+ #
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
Call Trace:
<TASK>
? rcu_read_unlock+0x17/0x60
dump_stack_lvl+0x77/0xb0
print_unlock_imbalance_bug+0xe0/0xf0
? rcu_read_unlock+0x17/0x60
lock_release+0x21d/0x2a0
rcu_read_unlock+0x1c/0x60
do_pte_missing+0x233/0xb40
__handle_mm_fault+0x80e/0xcd0
handle_mm_fault+0x146/0x310
do_user_addr_fault+0x303/0x880
exc_page_fault+0x9b/0x270
asm_exc_page_fault+0x26/0x30
RIP: 0033:0x5590e4eb41ea
Code: 61 cc 66 0f 6f e0 66 0f 61 c2 66 0f db cd 66 0f 69 e2 66 0f 6f d0 66 0f 69 d4 66 0f 61 0
RSP: 002b:00007ffcad25f030 EFLAGS: 00010202
RAX: 00005590e4eb8010 RBX: 00007ffcad260f7d RCX: 00007f73c474d44d
RDX: 00005590e4eb80a0 RSI: 00005590e4eb503c RDI: 000000000000000f
RBP: 00005590e4eb70a0 R08: 0000000000000000 R09: 00007f73c483a680
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffcad25f180 R14: 00005590e4eb6dd8 R15: 00007f73c4869020
</TASK>
------------[ cut here ]------------
Fix this by explicitly tracking the RCU lock state, ensuring that
rcu_read_unlock() in get_non_dying_memcg_end() is strictly paired with the
lock acquisition, regardless of any runtime rebinding events.
Link: https://lore.kernel.org/20260428103108.45719-1-qi.zheng@linux.dev
Fixes: 8285917d6f38 ("mm: memcontrol: prepare for reparenting non-hierarchical stats")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/memcontrol.c | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)
--- a/mm/memcontrol.c~mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end
+++ a/mm/memcontrol.c
@@ -805,12 +805,17 @@ static long memcg_state_val_in_pages(int
* Used in mod_memcg_state() and mod_memcg_lruvec_state() to avoid race with
* reparenting of non-hierarchical state_locals.
*/
-static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg)
+static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg,
+ bool *rcu_locked)
{
- if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+ /* Rebinding can cause this value to be changed at runtime */
+ if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
+ *rcu_locked = false;
return memcg;
+ }
rcu_read_lock();
+ *rcu_locked = true;
while (memcg_is_dying(memcg))
memcg = parent_mem_cgroup(memcg);
@@ -818,20 +823,21 @@ static inline struct mem_cgroup *get_non
return memcg;
}
-static inline void get_non_dying_memcg_end(void)
+static inline void get_non_dying_memcg_end(bool rcu_locked)
{
- if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+ if (!rcu_locked)
return;
rcu_read_unlock();
}
#else
-static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg)
+static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg,
+ bool *rcu_locked)
{
return memcg;
}
-static inline void get_non_dying_memcg_end(void)
+static inline void get_non_dying_memcg_end(bool rcu_locked)
{
}
#endif
@@ -865,12 +871,14 @@ static void __mod_memcg_state(struct mem
void mod_memcg_state(struct mem_cgroup *memcg, enum memcg_stat_item idx,
int val)
{
+ bool rcu_locked;
+
if (mem_cgroup_disabled())
return;
- memcg = get_non_dying_memcg_start(memcg);
+ memcg = get_non_dying_memcg_start(memcg, &rcu_locked);
__mod_memcg_state(memcg, idx, val);
- get_non_dying_memcg_end();
+ get_non_dying_memcg_end(rcu_locked);
}
#ifdef CONFIG_MEMCG_V1
@@ -933,14 +941,15 @@ static void mod_memcg_lruvec_state(struc
struct pglist_data *pgdat = lruvec_pgdat(lruvec);
struct mem_cgroup_per_node *pn;
struct mem_cgroup *memcg;
+ bool rcu_locked;
pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
- memcg = get_non_dying_memcg_start(pn->memcg);
+ memcg = get_non_dying_memcg_start(pn->memcg, &rcu_locked);
pn = memcg->nodeinfo[pgdat->node_id];
__mod_memcg_lruvec_state(pn, idx, val);
- get_non_dying_memcg_end();
+ get_non_dying_memcg_end(rcu_locked);
}
/**
_
Patches currently in -mm which might be from zhengqi.arch@bytedance.com are
mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch
^ permalink raw reply [flat|nested] 2+ messages in thread* + mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch added to mm-hotfixes-unstable branch
@ 2026-04-29 10:46 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-04-29 10:46 UTC (permalink / raw)
To: mm-commits, shakeel.butt, roman.gushchin, muchun.song, mhocko,
hannes, zhengqi.arch, akpm
The patch titled
Subject: mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Qi Zheng <zhengqi.arch@bytedance.com>
Subject: mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end()
Date: Wed, 29 Apr 2026 15:31:05 +0800
Currently, get_non_dying_memcg_start() and get_non_dying_memcg_end() both
evaluate cgroup_subsys_on_dfl(memory_cgrp_subsys) independently to
determine whether to acquire or release the RCU read lock.
However, the result of cgroup_subsys_on_dfl() can change dynamically at
runtime due to cgroup hierarchy rebinding (e.g., when the memory
controller is moved between cgroup v1 and v2 hierarchies). This can cause
the following warning:
=====================================
WARNING: bad unlock balance detected!
7.0.0-next-20260420+ #83 Tainted: G W
-------------------------------------
memcg-repro/270 is trying to release lock (rcu_read_lock) at:
[<ffffffff815f57f7>] rcu_read_unlock+0x17/0x60
but there are no more locks to release!
other info that might help us debug this:
1 lock held by memcg-repro/270:
#0: ffff888102fa2088 (vm_lock){++++}-{0:0}, at: do_user_addr_fault+0x285/0x880
stack backtrace:
CPU: 0 UID: 0 PID: 270 Comm: memcg-repro Tainted: G W 7.0.0-next-20260420+ #
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
Call Trace:
<TASK>
? rcu_read_unlock+0x17/0x60
dump_stack_lvl+0x77/0xb0
print_unlock_imbalance_bug+0xe0/0xf0
? rcu_read_unlock+0x17/0x60
lock_release+0x21d/0x2a0
rcu_read_unlock+0x1c/0x60
do_pte_missing+0x233/0xb40
__handle_mm_fault+0x80e/0xcd0
handle_mm_fault+0x146/0x310
do_user_addr_fault+0x303/0x880
exc_page_fault+0x9b/0x270
asm_exc_page_fault+0x26/0x30
RIP: 0033:0x5590e4eb41ea
Code: 61 cc 66 0f 6f e0 66 0f 61 c2 66 0f db cd 66 0f 69 e2 66 0f 6f d0 66 0f 69 d4 66 0f 61 0
RSP: 002b:00007ffcad25f030 EFLAGS: 00010202
RAX: 00005590e4eb8010 RBX: 00007ffcad260f7d RCX: 00007f73c474d44d
RDX: 00005590e4eb80a0 RSI: 00005590e4eb503c RDI: 000000000000000f
RBP: 00005590e4eb70a0 R08: 0000000000000000 R09: 00007f73c483a680
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffcad25f180 R14: 00005590e4eb6dd8 R15: 00007f73c4869020
</TASK>
------------[ cut here ]------------
Fix this by explicitly tracking the RCU lock state, ensuring that
rcu_read_unlock() in get_non_dying_memcg_end() is strictly paired with the
lock acquisition, regardless of any runtime rebinding events.
Link: https://lore.kernel.org/20260429073105.44472-1-qi.zheng@linux.dev
Fixes: 8285917d6f38 ("mm: memcontrol: prepare for reparenting non-hierarchical stats")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/memcontrol.c | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)
--- a/mm/memcontrol.c~mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end
+++ a/mm/memcontrol.c
@@ -805,12 +805,17 @@ static long memcg_state_val_in_pages(int
* Used in mod_memcg_state() and mod_memcg_lruvec_state() to avoid race with
* reparenting of non-hierarchical state_locals.
*/
-static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg)
+static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg,
+ bool *rcu_locked)
{
- if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+ /* Rebinding can cause this value to be changed at runtime */
+ if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
+ *rcu_locked = false;
return memcg;
+ }
rcu_read_lock();
+ *rcu_locked = true;
while (memcg_is_dying(memcg))
memcg = parent_mem_cgroup(memcg);
@@ -818,20 +823,21 @@ static inline struct mem_cgroup *get_non
return memcg;
}
-static inline void get_non_dying_memcg_end(void)
+static inline void get_non_dying_memcg_end(bool rcu_locked)
{
- if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+ if (!rcu_locked)
return;
rcu_read_unlock();
}
#else
-static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg)
+static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg,
+ bool *rcu_locked)
{
return memcg;
}
-static inline void get_non_dying_memcg_end(void)
+static inline void get_non_dying_memcg_end(bool rcu_locked)
{
}
#endif
@@ -865,12 +871,14 @@ static void __mod_memcg_state(struct mem
void mod_memcg_state(struct mem_cgroup *memcg, enum memcg_stat_item idx,
int val)
{
+ bool rcu_locked = false;
+
if (mem_cgroup_disabled())
return;
- memcg = get_non_dying_memcg_start(memcg);
+ memcg = get_non_dying_memcg_start(memcg, &rcu_locked);
__mod_memcg_state(memcg, idx, val);
- get_non_dying_memcg_end();
+ get_non_dying_memcg_end(rcu_locked);
}
#ifdef CONFIG_MEMCG_V1
@@ -933,14 +941,15 @@ static void mod_memcg_lruvec_state(struc
struct pglist_data *pgdat = lruvec_pgdat(lruvec);
struct mem_cgroup_per_node *pn;
struct mem_cgroup *memcg;
+ bool rcu_locked = false;
pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
- memcg = get_non_dying_memcg_start(pn->memcg);
+ memcg = get_non_dying_memcg_start(pn->memcg, &rcu_locked);
pn = memcg->nodeinfo[pgdat->node_id];
__mod_memcg_lruvec_state(pn, idx, val);
- get_non_dying_memcg_end();
+ get_non_dying_memcg_end(rcu_locked);
}
/**
_
Patches currently in -mm which might be from zhengqi.arch@bytedance.com are
mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-04-29 10:46 UTC | newest]
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