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futex: Fix errors in nested key ref-counting 

futex_wait() is leaking key references due to futex_wait_setup()
acquiring an additional reference via the queue_lock() routine. The
nested key ref-counting has been masking bugs and complicating code
analysis. queue_lock() is only called with a previously ref-counted
key, so remove the additional ref-counting from the queue_(un)lock()
functions.

Also futex_wait_requeue_pi() drops one key reference too many in
unqueue_me_pi(). Remove the key reference handling from
unqueue_me_pi(). This was paired with a queue_lock() in
futex_lock_pi(), so the count remains unchanged.

Document remaining nested key ref-counting sites.

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Reported-and-tested-by: Matthieu Fertré<matthieu.fertre@kerlabs.com>
Reported-by: Louis Rilling<louis.rilling@kerlabs.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <4CBB17A8.70401@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
This commit is contained in:
Darren Hart 2010-10-17 08:35:04 -07:00 committed by Thomas Gleixner
parent 2b666ca4a6
commit 7ada876a87
1 changed files with 16 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
kernel/futex.c
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@ -1363,7 +1363,6 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
{
struct futex_hash_bucket *hb;
get_futex_key_refs(&q->key);
hb = hash_futex(&q->key);
q->lock_ptr = &hb->lock;
@ -1375,7 +1374,6 @@ static inline void
queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
{
spin_unlock(&hb->lock);
drop_futex_key_refs(&q->key);
}
/**
@ -1480,8 +1478,6 @@ static void unqueue_me_pi(struct futex_q *q)
q->pi_state = NULL;
spin_unlock(q->lock_ptr);
drop_futex_key_refs(&q->key);
}
/*
@ -1812,7 +1808,10 @@ static int futex_wait(u32 __user *uaddr, int fshared,
}
retry:
/* Prepare to wait on uaddr. */
/*
* Prepare to wait on uaddr. On success, holds hb lock and increments
* q.key refs.
*/
ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
if (ret)
goto out;
@ -1822,24 +1821,23 @@ retry:
/* If we were woken (and unqueued), we succeeded, whatever. */
ret = 0;
/* unqueue_me() drops q.key ref */
if (!unqueue_me(&q))
goto out_put_key;
goto out;
ret = -ETIMEDOUT;
if (to && !to->task)
goto out_put_key;
goto out;
/*
* We expect signal_pending(current), but we might be the
* victim of a spurious wakeup as well.
*/
if (!signal_pending(current)) {
put_futex_key(fshared, &q.key);
if (!signal_pending(current))
goto retry;
}
ret = -ERESTARTSYS;
if (!abs_time)
goto out_put_key;
goto out;
restart = &current_thread_info()->restart_block;
restart->fn = futex_wait_restart;
@ -1856,8 +1854,6 @@ retry:
ret = -ERESTART_RESTARTBLOCK;
out_put_key:
put_futex_key(fshared, &q.key);
out:
if (to) {
hrtimer_cancel(&to->timer);
@ -2236,7 +2232,10 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
q.rt_waiter = &rt_waiter;
q.requeue_pi_key = &key2;
/* Prepare to wait on uaddr. */
/*
* Prepare to wait on uaddr. On success, increments q.key (key1) ref
* count.
*/
ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
if (ret)
goto out_key2;
@ -2254,7 +2253,9 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
* In order for us to be here, we know our q.key == key2, and since
* we took the hb->lock above, we also know that futex_requeue() has
* completed and we no longer have to concern ourselves with a wakeup
* race with the atomic proxy lock acquition by the requeue code.
* race with the atomic proxy lock acquisition by the requeue code. The
* futex_requeue dropped our key1 reference and incremented our key2
* reference count.
*/
/* Check if the requeue code acquired the second futex for us. */