[tip: timers/core] futex: Use accessor for hrtimer_sleeper ->task field in waitwake.c

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     fa3d486086d6948a6cf09b6d94cb1f56df2b1a6b
Gitweb:        https://git.kernel.org/tip/fa3d486086d6948a6cf09b6d94cb1f56df2b1a6b
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Fri, 18 Sep 2026 17:14:21 -07:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxx>
CommitterDate: Tue, 29 Sep 2026 21:02:51 +02:00

futex: Use accessor for hrtimer_sleeper ->task field in waitwake.c

The hrtimer_sleeper structure's ->task field is used as a flag to indicate
that the associated hrtimer has expired.  This means that the hrtimer
handler can be storing to this field while other code is loading from it
to check for expiry.  Note that additional races appear for hrtimers that
can be restarted, which could be argued to be a user error.  However, that
is no reason to let the compiler introduce additional confusion, and to
this end, the hrtimer_sleeper_task_get() was introduced, use of which also
has the benefit of avoiding open-code access to hrtimer_sleeper innards.

Therefore, apply this accessor to kernel/futex/waitwake.c.

KCSAN located this issue.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Reviewed-by: André Almeida <andrealmeid@xxxxxxxxxx>
Reviewed-by: Dmitry Ilvokhin <d@xxxxxxxxxxxx>
Link: https://patch.msgid.link/20260919001428.3133388-5-paulmck@xxxxxxxxxx
---
 kernel/futex/waitwake.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
index d4483d1..cf18309 100644
--- a/kernel/futex/waitwake.c
+++ b/kernel/futex/waitwake.c
@@ -383,7 +383,7 @@ void futex_do_wait(struct futex_q *q, struct hrtimer_sleeper *timeout)
 		 * flagged for rescheduling. Only call schedule if there
 		 * is no timeout, or if it has yet to expire.
 		 */
-		if (!timeout || timeout->task)
+		if (!timeout || hrtimer_sleeper_task_get(timeout))
 			schedule();
 	}
 	__set_current_state(TASK_RUNNING);
@@ -539,7 +539,7 @@ retry:
 static void futex_sleep_multiple(struct futex_vector *vs, unsigned int count,
 				 struct hrtimer_sleeper *to)
 {
-	if (to && !to->task)
+	if (to && !hrtimer_sleeper_task_get(to))
 		return;
 
 	for (; count; count--, vs++) {
@@ -590,7 +590,7 @@ int futex_wait_multiple(struct futex_vector *vs, unsigned int count,
 		if (ret >= 0)
 			return ret;
 
-		if (to && !to->task)
+		if (to && !hrtimer_sleeper_task_get(to))
 			return -ETIMEDOUT;
 		else if (signal_pending(current))
 			return -ERESTARTSYS;
@@ -725,7 +725,7 @@ retry:
 	if (!futex_unqueue(&q))
 		return 0;
 
-	if (to && !to->task)
+	if (to && !hrtimer_sleeper_task_get(to))
 		return -ETIMEDOUT;
 
 	/*