mm/ksm: avoid missing ksmd wakeups in ksm_enter

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__ksm_enter() decides whether ksmd needs a wakeup by checking if the mm
slot list is empty before inserting the new slot.

The empty check is currently outside ksm_mmlist_lock.  Another CPU can
remove the last slot and let ksmd go back to sleep after the unlocked
check, while this CPU inserts a new slot and skips the wakeup based on the
stale result.

Take ksm_mmlist_lock before checking the list so the empty-to-nonempty
transition and the insertion are observed as one critical section.

Link: https://lore.kernel.org/20260805132736.1063408-1-xialonglong2025@163.com
Fixes: 6e15838425 ("ksm: keep quiet while list empty")
Signed-off-by: Longlong Xia <xialonglong@kylinos.cn>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

...

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Longlong Xia 2026-08-05 21:27:34 +08:00 • committed by Andrew Morton

parent 2bee308f3a

commit 3c37cac718

1 changed files with 1 additions and 2 deletions

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mm/ksm.c

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