PT-2026-51871 · Linux · Linux
Published
2026-06-24
·
Updated
2026-06-24
·
CVE-2026-52977
None
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In the Linux kernel, the following vulnerability has been resolved:
futex: Prevent lockup in requeue-PI during signal/ timeout wakeup
During wait-requeue-pi (task A) and requeue-PI (task B) the following
race can happen:
Task A Task B
futex wait requeue pi()
futex setup timer()
futex do wait()
futex requeue()
CLASS(hb, hb1)(&key1);
CLASS(hb, hb2)(&key2);
timeout
futex requeue pi wakeup sync()
requeue state = Q REQUEUE PI IGNORE
blocks on hb->lock
futex proxy trylock atomic()
futex requeue pi prepare()
Q REQUEUE PI IGNORE => -EAGAIN
double unlock hb(hb1, hb2)
*retry*Task B acquires both hb locks and attempts to acquire the PI-lock of the
top most waiter (task B). Task A is leaving early due to a signal/
timeout and started removing itself from the queue. It updates its
requeue state but can not remove it from the list because this requires
the hb lock which is owned by task B.
Usually task A is able to swoop the lock after task B unlocked it.
However if task B is of higher priority then task A may not be able to
wake up in time and acquire the lock before task B gets it again.
Especially on a UP system where A is never scheduled.
As a result task A blocks on the lock and task B busy loops, trying to
make progress but live locks the system instead. Tragic.
This can be fixed by removing the top most waiter from the list in this
case. This allows task B to grab the next top waiter (if any) in the
next iteration and make progress.
Remove the top most waiter if futex requeue pi prepare() fails.
Let the waiter conditionally remove itself from the list in
handle early requeue pi wakeup().
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Related Identifiers
Affected Products
Linux