summaryrefslogtreecommitdiff
path: root/kernel
diff options
context:
space:
mode:
authorBrian Silverman <bsilver16384@gmail.com>2014-10-25 20:20:37 -0400
committerBen Hutchings <ben@decadent.org.uk>2014-12-14 16:23:51 +0000
commita708b76a5c74624ac0bb5a70c892511536c37869 (patch)
tree54701d227e01bf7fbf45c1c87deab0d3f3c74780 /kernel
parent3cd3a349aa3519b88d29845c0bc36bcbae158e93 (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.c22
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;
}