[PATCH RFC 2/9] aio: Use accessor for hrtimer_sleeper ->task field

[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.

KCSAN located this issue.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Benjamin LaHaise <bcrl@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
Cc: <linux-aio@xxxxxxxxx>
Cc: <linux-fsdevel@xxxxxxxxxxxxxxx>
---
 fs/aio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/aio.c b/fs/aio.c
index f57fa21a250353..e8cd65fce41eba 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1402,7 +1402,7 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
 		w.min_nr = min_nr - ret;
 
 		ret2 = prepare_to_wait_event(&ctx->wait, &w.w, TASK_INTERRUPTIBLE);
-		if (!ret2 && !t.task)
+		if (!ret2 && !hrtimer_sleeper_task_get(&t))
 			ret2 = -ETIME;
 
 		if (aio_read_events(ctx, min_nr, nr, event, &ret) || ret2)
-- 
2.40.1