futex: Ensure the correct return value from futex_lock_pi()

In case that futex_lock_pi() was aborted by a signal or a timeout and the
task returned without acquiring the rtmutex, but is the designated owner of
the futex due to a concurrent futex_unlock_pi() fixup_owner() is invoked to
establish consistent state. In that case it invokes fixup_pi_state_owner()
which in turn tries to acquire the rtmutex again. If that succeeds then it
does not propagate this success to fixup_owner() and futex_lock_pi()
returns -EINTR or -ETIMEOUT despite having the futex locked.

Return success from fixup_pi_state_owner() in all cases where the current
task owns the rtmutex and therefore the futex and propagate it correctly
through fixup_owner(). Fixup the other callsite which does not expect a
positive return value.

Fixes: c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org

diff --git a/kernel/futex.c b/kernel/futex.c
index c47d101..d5e61c2 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2373,8 +2373,8 @@ retry:
                }
 
                if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
-                       /* We got the lock after all, nothing to fix. */
-                       ret = 0;
+                       /* We got the lock. pi_state is correct. Tell caller. */
+                       ret = 1;
                        goto out_unlock;
                }
 
@@ -2402,7 +2402,7 @@ retry:
                         * We raced against a concurrent self; things are
                         * already fixed up. Nothing to do.
                         */
-                       ret = 0;
+                       ret = 1;
                        goto out_unlock;
                }
                newowner = argowner;
@@ -2448,7 +2448,7 @@ retry:
        raw_spin_unlock(&newowner->pi_lock);
        raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
 
-       return 0;
+       return argowner == current;
 
        /*
         * In order to reschedule or handle a page fault, we need to drop the
@@ -2490,7 +2490,7 @@ handle_err:
         * Check if someone else fixed it for us:
         */
        if (pi_state->owner != oldowner) {
-               ret = 0;
+               ret = argowner == current;
                goto out_unlock;
        }
 
@@ -2523,8 +2523,6 @@ static long futex_wait_restart(struct restart_block *restart);
  */
 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
 {
-       int ret = 0;
-
        if (locked) {
                /*
                 * Got the lock. We might not be the anticipated owner if we
@@ -2535,8 +2533,8 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
                 * stable state, anything else needs more attention.
                 */
                if (q->pi_state->owner != current)
-                       ret = fixup_pi_state_owner(uaddr, q, current);
-               return ret ? ret : locked;
+                       return fixup_pi_state_owner(uaddr, q, current);
+               return 1;
        }
 
        /*
@@ -2547,10 +2545,8 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
         * Another speculative read; pi_state->owner == current is unstable
         * but needs our attention.
         */
-       if (q->pi_state->owner == current) {
-               ret = fixup_pi_state_owner(uaddr, q, NULL);
-               return ret;
-       }
+       if (q->pi_state->owner == current)
+               return fixup_pi_state_owner(uaddr, q, NULL);
 
        /*
         * Paranoia check. If we did not take the lock, then we should not be
@@ -2563,7 +2559,7 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
                                q->pi_state->owner);
        }
 
-       return ret;
+       return 0;
 }
 
 /**
@@ -3261,7 +3257,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
                if (q.pi_state && (q.pi_state->owner != current)) {
                        spin_lock(q.lock_ptr);
                        ret = fixup_pi_state_owner(uaddr2, &q, current);
-                       if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
+                       if (ret < 0 && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
                                pi_state = q.pi_state;
                                get_pi_state(pi_state);
                        }
@@ -3271,6 +3267,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
                         */
                        put_pi_state(q.pi_state);
                        spin_unlock(q.lock_ptr);
+                       /*
+                        * Adjust the return value. It's either -EFAULT or
+                        * success (1) but the caller expects 0 for success.
+                        */
+                       ret = ret < 0 ? ret : 0;
                }
        } else {
                struct rt_mutex *pi_mutex;