From 7ada876a8703f23befbb20a7465a702ee39b1704 Mon Sep 17 00:00:00 2001 From: Darren Hart Date: Sun, 17 Oct 2010 08:35:04 -0700 Subject: [PATCH] futex: Fix errors in nested key ref-counting MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Reported-and-tested-by: Matthieu Fertré Reported-by: Louis Rilling Cc: Peter Zijlstra Cc: Eric Dumazet Cc: John Kacur Cc: Rusty Russell LKML-Reference: <4CBB17A8.70401@linux.intel.com> Signed-off-by: Thomas Gleixner Cc: stable@kernel.org --- kernel/futex.c | 31 ++++++++++++++++--------------- 1 file 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 = ¤t_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. */ -- 2.30.2