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| author | Peter Zijlstra <peterz@infradead.org> | 2021-03-28 22:42:32 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-03-30 14:41:42 +0200 |
| commit | 5083fb83381fd011fe4a8e84b7089fcde8cfcb25 (patch) | |
| tree | 6152d3bc1e074a17c1dfc507bb74c2528cff9f23 | |
| parent | b4f92d8dec9ba55c6d68cd190f139c682e9700ae (diff) | |
| download | linux-stable-5083fb83381fd011fe4a8e84b7089fcde8cfcb25.tar.gz linux-stable-5083fb83381fd011fe4a8e84b7089fcde8cfcb25.tar.bz2 linux-stable-5083fb83381fd011fe4a8e84b7089fcde8cfcb25.zip | |
futex: Fix (possible) missed wakeup
commit b061c38bef43406df8e73c5be06cbfacad5ee6ad upstream.
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 60be2d3cfdd7..5677fbb97aea 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1553,11 +1553,7 @@ 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 @@ -1566,6 +1562,13 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) * store to lock_ptr from getting ahead of the plist_del. */ 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); } /* |