[PATCH 25/46] mm/userfaultfd: wake waiters when registration modes are removed

[sashiko-bot at kernel.org]

> UFFDIO_REGISTER can replace MISSING or MINOR tracking without waking
> faults that are already queued. For example, switching an anonymous
> range from MISSING to WP leaves a missing-fault waiter asleep until
> userspace explicitly wakes it.
> 
> When a registration change removes a UFFD mode, wake waiters in the
> affected interval after updating the VMA. The VMA is write-locked at
> this point, so no new faults can queue under the old modes and woken
> threads cannot retry until mmap_write_unlock(). Waiters for retained
> modes in the same interval may also wake and refault.
> 
> The hang reproduces for MISSING-to-WP and MINOR-to-MISSING transitions,
> with both read and unread fault events.
> 
> Fixes: 63b2d4174c4a ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl")
> Cc: stable at vger.kernel.org
> Signed-off-by: David Hildenbrand (Arm) <david at kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org?part=25