1 files changed, 22 insertions, 19 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 3717e7b306e0..20ef219bbe9b 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -716,7 +716,7 @@ static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
                                 struct futex_pi_state **ps,
                                 struct task_struct *task, int set_waiters)
 {
-        int lock_taken, ret, ownerdied = 0;
+        int lock_taken, ret, force_take = 0;
         u32 uval, newval, curval, vpid = task_pid_vnr(task);
 
 retry:
@@ -755,17 +755,15 @@ retry:
         newval = curval | FUTEX_WAITERS;
 
         /*
-         * There are two cases, where a futex might have no owner (the
-         * owner TID is 0): OWNER_DIED. We take over the futex in this
-         * case. We also do an unconditional take over, when the owner
-         * of the futex died.
-         *
-         * This is safe as we are protected by the hash bucket lock !
+         * Should we force take the futex? See below.
          */
-        if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
-                /* Keep the OWNER_DIED bit */
+        if (unlikely(force_take)) {
+                /*
+                 * Keep the OWNER_DIED and the WAITERS bit and set the
+                 * new TID value.
+                 */
                 newval = (curval & ~FUTEX_TID_MASK) | vpid;
-                ownerdied = 0;
+                force_take = 0;
                 lock_taken = 1;
         }
 
@@ -775,7 +773,7 @@ retry:
                 goto retry;
 
         /*
-         * We took the lock due to owner died take over.
+         * We took the lock due to forced take over.
          */
         if (unlikely(lock_taken))
                 return 1;
@@ -790,20 +788,25 @@ retry:
                 switch (ret) {
                 case -ESRCH:
                         /*
-                         * No owner found for this futex. Check if the
-                         * OWNER_DIED bit is set to figure out whether
-                         * this is a robust futex or not.
+                         * We failed to find an owner for this
+                         * futex. So we have no pi_state to block
+                         * on. This can happen in two cases:
+                         *
+                         * 1) The owner died
+                         * 2) A stale FUTEX_WAITERS bit
+                         *
+                         * Re-read the futex value.
                          */
                         if (get_futex_value_locked(&curval, uaddr))
                                 return -EFAULT;
 
                         /*
-                         * We simply start over in case of a robust
-                         * futex. The code above will take the futex
-                         * and return happy.
+                         * If the owner died or we have a stale
+                         * WAITERS bit the owner TID in the user space
+                         * futex is 0.
                          */
-                        if (curval & FUTEX_OWNER_DIED) {
-                                ownerdied = 1;
+                        if (!(curval & FUTEX_TID_MASK)) {
+                                force_take = 1;
                                 goto retry;
                         }
                 default: