futex/requeue: Prevent NULL pointer dereference in remove_waiter() on self-deadlock

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When FUTEX_CMP_REQUEUE_PI requeues a non-top waiter that already owns the
target PI futex, task_blocks_on_rt_mutex() returns -EDEADLK before setting
waiter->task.

The subsequent remove_waiter() in rt_mutex_start_proxy_lock() dereferences
the NULL waiter->task, causing a kernel crash.

Add a self-deadlock check for non-top waiters before calling
rt_mutex_start_proxy_lock(), analogous to the top-waiter check in
futex_lock_pi_atomic().

Fixes: 3bfdc63936 ("rtmutex: Use waiter::task instead of current in remove_waiter()")
Signed-off-by: Ji'an Zhou <eilaimemedsnaimel@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org

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Ji'an Zhou 2026-06-02 09:12:04 +00:00 • committed by Thomas Gleixner

parent e43ffb69e0

commit 74e144274a

1 changed files with 6 additions and 0 deletions

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kernel/futex/requeue.c

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