| From | Kamal Mostafa <> | Subject | [PATCH 3.13 139/162] futex: Fix a race condition between REQUEUE_PI and task death | Date | Thu, 6 Nov 2014 14:36:43 -0800 |
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3.13.11.11 -stable review patch. If anyone has any objections, please let me know.
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From: Brian Silverman <bsilver16384@gmail.com>
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> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- kernel/futex.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c index 2b1583e..7947e4c 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -492,8 +492,14 @@ 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; @@ -1407,15 +1413,6 @@ 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; @@ -1503,6 +1500,8 @@ 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); @@ -1512,6 +1511,8 @@ 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); @@ -1588,6 +1589,7 @@ retry_private: } out_unlock: + free_pi_state(pi_state); double_unlock_hb(hb1, hb2); /* @@ -1604,8 +1606,6 @@ 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; } -- 1.9.1
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