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 <[email protected]>
Signed-off-by: Darren Hart <[email protected]>
Cc: <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Dinakar Guniguntala <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Sven-Thorsten Dietrich <[email protected]>
Cc: John Kacur <[email protected]>
LKML-Reference: <4AD7A298.5040802@us.ibm.com>
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/kernel/futex.c b/kernel/futex.c
index 06938e560ac9e832e11a044824589622be8f2efd..642f3bbaacc7483221ec76aaeb6b1b080b5b8c8f 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -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 @@ retry_private:
                 */
                if (ret == 1) {
                        WARN_ON(pi_state);
+                       drop_count++;
                        task_count++;
                        ret = get_futex_value_locked(&curval2, uaddr2);
                        if (!ret)
@@ -1305,6 +1305,7 @@ retry_private:
                        if (ret == 1) {
                                /* We got the lock. */
                                requeue_pi_wake_futex(this, &key2, hb2);
+                               drop_count++;
                                continue;
                        } else if (ret) {
                                /* -EDEADLK */