futex: fix reference leak
Peter Zijlstra [Wed, 11 Feb 2009 17:10:10 +0000 (18:10 +0100)]
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.

Reported-by: Catalin Marinas <catalin.marinas@arm.com>
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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/futex.c

index f89d373..438701a 100644 (file)
@@ -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;
@@ -1216,11 +1217,13 @@ retry:
 
                if (!ret)
                        goto retry;
-               return ret;
+               goto out;
        }
        ret = -EWOULDBLOCK;
-       if (uval != val)
-               goto out_unlock_put_key;
+       if (unlikely(uval != val)) {
+               queue_unlock(&q, hb);
+               goto out_put_key;
+       }
 
        /* Only actually queue if *uaddr contained val.  */
        queue_me(&q, hb);
@@ -1284,38 +1287,38 @@ 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;
 }