diff options
author | Brian Silverman <bsilver16384@gmail.com> | 2014-10-25 20:20:37 -0400 |
---|---|---|
committer | Zefan Li <lizefan@huawei.com> | 2015-02-02 17:05:05 +0800 |
commit | b1a76f1c42ec736247cd9a789d67532f7f2a1d31 (patch) | |
tree | 0aa981018542362f019b490aeda77b202bd890a3 /kernel | |
parent | aab6a6fa71741bb96288b634d4506e1630dba46a (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>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@huawei.com>
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 fafc54fef885..6b320c2ad6fa 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -486,8 +486,14 @@ 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; @@ -1401,15 +1407,6 @@ 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; @@ -1497,6 +1494,8 @@ 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); @@ -1506,6 +1505,8 @@ 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); @@ -1582,6 +1583,7 @@ retry_private: } out_unlock: + free_pi_state(pi_state); double_unlock_hb(hb1, hb2); /* @@ -1598,8 +1600,6 @@ 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; } |