[PATCH 07/46] mm/filemap: don't lose a folio lock wakeup to a signal

[Rik van Riel]

On Tue, 2026-10-27 at 00:17 +0100, David Hildenbrand (Arm) wrote:
> From: Josef Bacik <josef at toxicpanda.com>
> 
> An exclusive waiter in folio_wait_bit_common() can leave the wait
> loop
> because of a fatal signal, then be woken by folio_unlock() before
> finish_wait(). If the waker did not hand over the lock, the waiter
> returns
> -EINTR without trying to acquire it.
> 
> folio_wake_bit() stops after waking the first exclusive waiter, so
> this
> loses the wakeup and can leave other waiters asleep indefinitely on
> an
> unlocked folio.
> 
> After finish_wait(), let a waiter woken without a lock handoff try
> once
> more to acquire the lock. If successful, return success so the
> caller's
> eventual unlock wakes the next waiter. Otherwise, the current lock
> owner
> will do so.
> 
> Fix generated by an LLM and sent by Josef Bacik in private.
> 
> Fixes: 5ef64cc8987a ("mm: allow a controlled amount of unfairness in
> the page lock")
> Cc: stable at vger.kernel.org
> Signed-off-by: Josef Bacik <josef at toxicpanda.com>
> [ david: clarify and simplify comment + description ]
> Signed-off-by: David Hildenbrand (Arm) <david at kernel.org>

Reviewed-by: Rik van Riel <riel at surriel.com>

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