[PATCH RFC 9/9] futex: Use accessor for hrtimer_sleeper ->task field in requeue

[Paul E. McKenney]

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 handle_early_requeue_pi_wakeup().

KCSAN located this issue.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Darren Hart <dvhart@xxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: "André Almeida" <andrealmeid@xxxxxxxxxx>
Cc: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
---
 kernel/futex/requeue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/futex/requeue.c b/kernel/futex/requeue.c
index 79823ad136830a..196d6ff148a4d8 100644
--- a/kernel/futex/requeue.c
+++ b/kernel/futex/requeue.c
@@ -736,7 +736,7 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
 
 	/* Handle spurious wakeups gracefully */
 	ret = -EWOULDBLOCK;
-	if (timeout && !timeout->task)
+	if (timeout && !hrtimer_sleeper_task_get(timeout))
 		ret = -ETIMEDOUT;
 	else if (signal_pending(current))
 		ret = -ERESTARTNOINTR;
-- 
2.40.1