[PATCH -v3] futex: fix reference leak

Peter Zijlstra
2009-02-11T15:35:29Z

So you prefer this version?

---
Subject: futex: fix reference leak
From: Peter Zijlstra <peterz@infradead.org>

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.

This regression was discovered by kmemleak.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
Tested-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Catalin Marinas <catalin.marinas@arm.com>
---
kernel/futex.c | 51 ++++++++++++++++++++++++++++-----------------------
1 files changed, 28 insertions(+), 23 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index f89d373..a4b3cac 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1165,6 +1165,7 @@ static int futex_wait(u32 __user *uaddr, int fshared,
u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
{
struct task_struct *curr = current;
+ struct restart_block *restart;
DECLARE_WAITQUEUE(wait, curr);
struct futex_hash_bucket *hb;
struct futex_q q;
@@ -1216,7 +1217,7 @@ retry:

if (!ret)
goto retry;
- return ret;
+ goto out;
}
ret = -EWOULDBLOCK;
if (uval != val)
@@ -1284,40 +1285,44 @@ retry:
*/

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

/*
* We expect signal_pending(current), but another thread may
* have handled it for us already.
*/
+ ret = -ERESTARTSYS;
if (!abs_time)
- return -ERESTARTSYS;
- else {
- struct restart_block *restart;
- restart = &current_thread_info()->restart_block;
- restart->fn = futex_wait_restart;
- restart->futex.uaddr = (u32 *)uaddr;
- restart->futex.val = val;
- restart->futex.time = abs_time->tv64;
- restart->futex.bitset = bitset;
- restart->futex.flags = 0;
-
- if (fshared)
- restart->futex.flags |= FLAGS_SHARED;
- if (clockrt)
- restart->futex.flags |= FLAGS_CLOCKRT;
- return -ERESTART_RESTARTBLOCK;
- }
+ goto out_put_key;

-out_unlock_put_key:
- queue_unlock(&q, hb);
- put_futex_key(fshared, &q.key);
+ restart = &current_thread_info()->restart_block;
+ restart->fn = futex_wait_restart;
+ restart->futex.uaddr = (u32 *)uaddr;
+ restart->futex.val = val;
+ restart->futex.time = abs_time->tv64;
+ restart->futex.bitset = bitset;
+ restart->futex.flags = 0;

+ if (fshared)
+ restart->futex.flags |= FLAGS_SHARED;
+ if (clockrt)
+ restart->futex.flags |= FLAGS_CLOCKRT;
+
+ ret = -ERESTART_RESTARTBLOCK;
+
+out_put_key:
+ put_futex_key(fshared, &q.key);
out:
return ret;
+
+out_unlock_put_key:
+ queue_unlock(&q, hb);
+ goto out_put_key;
}