Merge tag 'locking-urgent-2026-05-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

cffcf520 · Linus Torvalds <[email protected]> · 2026-05-03 08:17:09 -07:00

Pull locking fix from Ingo Molnar:
 "Fix lockup in requeue-PI during signal/timeout wakeups, by Sebastian
  Andrzej Siewior"

* tag 'locking-urgent-2026-05-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Prevent lockup in requeue-PI during signal/ timeout wakeup

Commit: cffcf520fd69fe5a93b519cf0c7ccc5e467fcb1c
Parents: c3cba36b · bc7304f3

Merge commit. Changes below are compared with the first parent: c3cba36b.

Changes

1 files changed · +9 −4

File	Status	Add	Del	Content
kernel/futex/requeue.c	modified	+9	−4	View file

kernel/futex/requeue.c

View file

diff --git a/kernel/futex/requeue.c b/kernel/futex/requeue.c
index d818b4d..b597cb3 100644
--- a/kernel/futex/requeue.c
+++ b/kernel/futex/requeue.c
@@ -319,8 +319,11 @@ futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
 		return -EINVAL;
 
 	/* Ensure that this does not race against an early wakeup */
-	if (!futex_requeue_pi_prepare(top_waiter, NULL))
+	if (!futex_requeue_pi_prepare(top_waiter, NULL)) {
+		plist_del(&top_waiter->list, &hb1->chain);
+		futex_hb_waiters_dec(hb1);
 		return -EAGAIN;
+	}
 
 	/*
 	 * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
@@ -722,10 +725,12 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
 
 	/*
 	 * We were woken prior to requeue by a timeout or a signal.
-	 * Unqueue the futex_q and determine which it was.
+	 * Conditionally unqueue the futex_q and determine which it was.
 	 */
-	plist_del(&q->list, &hb->chain);
-	futex_hb_waiters_dec(hb);
+	if (!plist_node_empty(&q->list)) {
+		plist_del(&q->list, &hb->chain);
+		futex_hb_waiters_dec(hb);
+	}
 
 	/* Handle spurious wakeups gracefully */
 	ret = -EWOULDBLOCK;