diff options
| author | Brian Silverman <bsilver16384@gmail.com> | 2014-10-25 20:20:37 -0400 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2014-12-14 16:23:51 +0000 |
| commit | a708b76a5c74624ac0bb5a70c892511536c37869 (patch) | |
| tree | 54701d227e01bf7fbf45c1c87deab0d3f3c74780 /kernel | |
| parent | 3cd3a349aa3519b88d29845c0bc36bcbae158e93 (diff) | |
futex: Fix a race condition between REQUEUE_PI and task death
commit 30a6b8031fe14031ab27c1fa3483cb9780e7f63c upstream.
free_pi_state and exit_pi_state_list both clean up futex_pi_state's.
exit_pi_state_list takes the hb lock first, and most callers of
free_pi_state do too. requeue_pi doesn't, which means free_pi_state
can free the pi_state out from under exit_pi_state_list. For example:
task A | task B
exit_pi_state_list |
pi_state = |
curr->pi_state_list->next |
| futex_requeue(requeue_pi=1)
| // pi_state is the same as
| // the one in task A
| free_pi_state(pi_state)
| list_del_init(&pi_state->list)
| kfree(pi_state)
list_del_init(&pi_state->list) |
Move the free_pi_state calls in requeue_pi to before it drops the hb
locks which it's already holding.
[ tglx: Removed a pointless free_pi_state() call and the hb->lock held
debugging. The latter comes via a seperate patch ]
Signed-off-by: Brian Silverman <bsilver16384@gmail.com>
Cc: austin.linux@gmail.com
Cc: darren@dvhart.com
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/1414282837-23092-1-git-send-email-bsilver16384@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/futex.c | 22 |
1 files changed, 11 insertions, 11 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index f31f190ef4c4..74815953f54c 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -484,8 +484,14 @@ static struct futex_pi_state * alloc_pi_state(void) return pi_state; } +/* + * Must be called with the hb lock held. + */ static void free_pi_state(struct futex_pi_state *pi_state) { + if (!pi_state) + return; + if (!atomic_dec_and_test(&pi_state->refcount)) return; @@ -1399,15 +1405,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, } retry: - if (pi_state != NULL) { - /* - * We will have to lookup the pi_state again, so free this one - * to keep the accounting correct. - */ - free_pi_state(pi_state); - pi_state = NULL; - } - ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); if (unlikely(ret != 0)) goto out; @@ -1495,6 +1492,8 @@ retry_private: case 0: break; case -EFAULT: + free_pi_state(pi_state); + pi_state = NULL; double_unlock_hb(hb1, hb2); put_futex_key(&key2); put_futex_key(&key1); @@ -1504,6 +1503,8 @@ retry_private: goto out; case -EAGAIN: /* The owner was exiting, try again. */ + free_pi_state(pi_state); + pi_state = NULL; double_unlock_hb(hb1, hb2); put_futex_key(&key2); put_futex_key(&key1); @@ -1580,6 +1581,7 @@ retry_private: } out_unlock: + free_pi_state(pi_state); double_unlock_hb(hb1, hb2); /* @@ -1596,8 +1598,6 @@ out_put_keys: out_put_key1: put_futex_key(&key1); out: - if (pi_state != NULL) - free_pi_state(pi_state); return ret ? ret : task_count; } |