futex: fix reference leak

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>

1 files changed, 28 insertions, 25 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index f89d373a9c6d..438701adce23 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;
@@ -1216,11 +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;
 }