tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
1
fork

Configure Feed

Select the types of activity you want to include in your feed.

futex: Acquire a hash reference in futex_wait_multiple_setup()

futex_wait_multiple_setup() changes task_struct::__state to
!TASK_RUNNING and then enqueues on multiple futexes. Every
futex_q_lock() acquires a reference on the global hash which is
dropped later.

If a rehash is in progress then the loop will block on
mm_struct::futex_hash_bucket for the rehash to complete and this will
lose the previously set task_struct::__state.

Acquire a reference on the local hash to avoiding blocking on
mm_struct::futex_hash_bucket.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-9-bigeasy@linutronix.de

authored by

Sebastian Andrzej Siewior and committed by
Peter Zijlstra 3f6b2330 d854e4e7

+6
+6
kernel/futex/waitwake.c
··· 407 407 u32 uval; 408 408 409 409 /* 410 + * Make sure to have a reference on the private_hash such that we 411 + * don't block on rehash after changing the task state below. 412 + */ 413 + guard(private_hash)(); 414 + 415 + /* 410 416 * Enqueuing multiple futexes is tricky, because we need to enqueue 411 417 * each futex on the list before dealing with the next one to avoid 412 418 * deadlocking on the hash bucket. But, before enqueuing, we need to