CVE-2025-39977 futex: Prevent use-after-free during requeue-PI

In the Linux kernel, the following vulnerability has been resolved: futex: Prevent use-after-free during requeue-PI syzbot managed to trigger the following race: T1 T2 futexwaitrequeuepi futexdowait schedule futexrequeue futexproxytrylockatomic futexrequeuepiprepare requeuepiwakefutex...