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| author | Peter Zijlstra <peterz@infradead.org> | 2018-11-29 14:44:49 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-01-21 11:15:38 +0100 |
| commit | b061c38bef43406df8e73c5be06cbfacad5ee6ad (patch) | |
| tree | c031de9bb7878fd8a24cc0fb339151044e2fae12 | |
| parent | 4c4e3731564c8945ac5ac90fc2a1e1f21cb79c92 (diff) | |
| download | linux-b061c38bef43406df8e73c5be06cbfacad5ee6ad.tar.gz linux-b061c38bef43406df8e73c5be06cbfacad5ee6ad.tar.bz2 linux-b061c38bef43406df8e73c5be06cbfacad5ee6ad.zip | |
futex: Fix (possible) missed wakeup
We must not rely on wake_q_add() to delay the wakeup; in particular
commit:
1d0dcb3ad9d3 ("futex: Implement lockless wakeups")
moved wake_q_add() before smp_store_release(&q->lock_ptr, NULL), which
could result in futex_wait() waking before observing ->lock_ptr ==
NULL and going back to sleep again.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 1d0dcb3ad9d3 ("futex: Implement lockless wakeups")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | kernel/futex.c | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index be3bff2315ff..fdd312da0992 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1452,11 +1452,7 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) return; - /* - * Queue the task for later wakeup for after we've released - * the hb->lock. wake_q_add() grabs reference to p. - */ - wake_q_add(wake_q, p); + get_task_struct(p); __unqueue_futex(q); /* * The waiting task can free the futex_q as soon as q->lock_ptr = NULL @@ -1466,6 +1462,13 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) * plist_del in __unqueue_futex(). */ smp_store_release(&q->lock_ptr, NULL); + + /* + * Queue the task for later wakeup for after we've released + * the hb->lock. wake_q_add() grabs reference to p. + */ + wake_q_add(wake_q, p); + put_task_struct(p); } /* |