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futex: Move drop_futex_key_refs out of spinlock'ed region

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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>
This commit is contained in:
Darren Hart 2009-10-15 15:30:48 -07:00 committed by Ingo Molnar
parent 237c80c5c8
commit 89061d3d58
1 changed files with 2 additions and 1 deletions
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3
kernel/futex.c
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@ -1029,7 +1029,6 @@ static inline
void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
struct futex_hash_bucket *hb)
{
drop_futex_key_refs(&q->key);
get_futex_key_refs(key);
q->key = *key;
@ -1227,6 +1226,7 @@ static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
*/
if (ret == 1) {
WARN_ON(pi_state);
drop_count++;
task_count++;
ret = get_futex_value_locked(&curval2, uaddr2);
if (!ret)
@ -1305,6 +1305,7 @@ static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
if (ret == 1) {
/* We got the lock. */
requeue_pi_wake_futex(this, &key2, hb2);
drop_count++;
continue;
} else if (ret) {
/* -EDEADLK */