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authorDarren Hart <dvhart@linux.intel.com>2010-10-17 08:35:04 -0700
committerThomas Gleixner <tglx@linutronix.de>2010-10-19 11:41:54 +0200
commit7ada876a8703f23befbb20a7465a702ee39b1704 (patch)
treeadee9cf8676fed56a0a6ad1d270ae5fb84d32553 /kernel/futex.c
parent2b666ca4a68cbc22483b0f2e1ba3c0e59b01ae9e (diff)
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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
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c31
1 files changed, 16 insertions, 15 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 6a3a5fa1526d..e328f574c97c 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -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. */