Commit 89061d3d authored Oct 15, 2009 by Darren Hart Committed by Ingo Molnar Oct 16, 2009

futex: Move drop_futex_key_refs out of spinlock'ed region



When requeuing tasks from one futex to another, the reference held
by the requeued task to the original futex location needs to be
dropped eventually.

Dropping the reference may ultimately lead to a call to
"iput_final" and subsequently call into filesystem- specific code -
which may be non-atomic.

It is therefore safer to defer this drop operation until after the
futex_hash_bucket spinlock has been dropped.

Originally-From: Helge Bahmann <hcb@chaoticmind.net>
Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Cc: <stable@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Dinakar Guniguntala <dino@in.ibm.com>
Cc: John Stultz <johnstul@linux.vnet.ibm.com>
Cc: Sven-Thorsten Dietrich <sdietrich@novell.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <4AD7A298.5040802@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 237c80c5

kernel/futex.c

+2 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1029,7 +1029,6 @@ static inline
	void requeue_pi_wake_futex(struct futex_q q, union futex_key key,		void requeue_pi_wake_futex(struct futex_q q, union futex_key key,
	struct futex_hash_bucket *hb)		struct futex_hash_bucket *hb)
	{		{
	drop_futex_key_refs(&q->key);
	get_futex_key_refs(key);		get_futex_key_refs(key);
	q->key = *key;		q->key = *key;

	@@ -1227,6 +1226,7 @@ retry_private:
	*/		*/
	if (ret == 1) {		if (ret == 1) {
	WARN_ON(pi_state);		WARN_ON(pi_state);
			drop_count++;
	task_count++;		task_count++;
	ret = get_futex_value_locked(&curval2, uaddr2);		ret = get_futex_value_locked(&curval2, uaddr2);
	if (!ret)		if (!ret)
	@@ -1305,6 +1305,7 @@ retry_private:
	if (ret == 1) {		if (ret == 1) {
	/* We got the lock. */		/* We got the lock. */
	requeue_pi_wake_futex(this, &key2, hb2);		requeue_pi_wake_futex(this, &key2, hb2);
			drop_count++;
	continue;		continue;
	} else if (ret) {		} else if (ret) {
	/* -EDEADLK */		/* -EDEADLK */

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