[PATCH] futex: fix reference leak

Peter Zijlstra
2009-02-09T18:26:39Z

Venki, does this perchance solve your issue with my futex patch?

Darren, could you please have a look at this before Ingo pushes it out
to Linus?

---
Catalin noticed that (38d47c1b7075: futex: rely on
get_user_pages() for shared futexes) caused an mm_struct leak.

Some tracing with the function graph tracer quickly pointed out that
futex_wait() has exit paths with unbalanced reference counts.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/futex.c | 23 +++++++++++++++--------
1 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index f89d373..7b76c8e 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1284,18 +1284,23 @@ retry:
*/

/* If we were woken (and unqueued), we succeeded, whatever. */
- if (!unqueue_me(&q))
- return 0;
- if (rem)
- return -ETIMEDOUT;
+ if (!unqueue_me(&q)) {
+ ret = 0;
+ goto out_put_key;
+ }
+ if (rem) {
+ ret = -ETIMEDOUT;
+ goto out_put_key;
+ }

/*
* We expect signal_pending(current), but another thread may
* have handled it for us already.
*/
- if (!abs_time)
- return -ERESTARTSYS;
- else {
+ if (!abs_time) {
+ ret = -ERESTARTSYS;
+ goto out_put_key;
+ } else {
struct restart_block *restart;
restart = &current_thread_info()->restart_block;
restart->fn = futex_wait_restart;
@@ -1309,11 +1314,13 @@ retry:
restart->futex.flags |= FLAGS_SHARED;
if (clockrt)
restart->futex.flags |= FLAGS_CLOCKRT;
- return -ERESTART_RESTARTBLOCK;
+ ret = -RESTART_RESTARTBLOCK;
+ goto out_put_key;
}

out_unlock_put_key:
queue_unlock(&q, hb);
+out_put_key:
put_futex_key(fshared, &q.key);