futex: split out fixup owner logic from futex_lock_pi()
Darren Hart [Fri, 3 Apr 2009 20:40:02 +0000 (13:40 -0700)]
Refactor the post lock acquisition logic from futex_lock_pi(). This
code will be reused in futex_wait_requeue_pi().

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/futex.c

index 986b16e..af831fb 100644 (file)
@@ -1256,6 +1256,79 @@ handle_fault:
 static long futex_wait_restart(struct restart_block *restart);
 
 /**
+ * fixup_owner() - Post lock pi_state and corner case management
+ * @uaddr:     user address of the futex
+ * @fshared:   whether the futex is shared (1) or not (0)
+ * @q:         futex_q (contains pi_state and access to the rt_mutex)
+ * @locked:    if the attempt to take the rt_mutex succeeded (1) or not (0)
+ *
+ * After attempting to lock an rt_mutex, this function is called to cleanup
+ * the pi_state owner as well as handle race conditions that may allow us to
+ * acquire the lock. Must be called with the hb lock held.
+ *
+ * Returns:
+ *  1 - success, lock taken
+ *  0 - success, lock not taken
+ * <0 - on error (-EFAULT)
+ */
+static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
+                      int locked)
+{
+       struct task_struct *owner;
+       int ret = 0;
+
+       if (locked) {
+               /*
+                * Got the lock. We might not be the anticipated owner if we
+                * did a lock-steal - fix up the PI-state in that case:
+                */
+               if (q->pi_state->owner != current)
+                       ret = fixup_pi_state_owner(uaddr, q, current, fshared);
+               goto out;
+       }
+
+       /*
+        * Catch the rare case, where the lock was released when we were on the
+        * way back before we locked the hash bucket.
+        */
+       if (q->pi_state->owner == current) {
+               /*
+                * Try to get the rt_mutex now. This might fail as some other
+                * task acquired the rt_mutex after we removed ourself from the
+                * rt_mutex waiters list.
+                */
+               if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
+                       locked = 1;
+                       goto out;
+               }
+
+               /*
+                * pi_state is incorrect, some other task did a lock steal and
+                * we returned due to timeout or signal without taking the
+                * rt_mutex. Too late. We can access the rt_mutex_owner without
+                * locking, as the other task is now blocked on the hash bucket
+                * lock. Fix the state up.
+                */
+               owner = rt_mutex_owner(&q->pi_state->pi_mutex);
+               ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
+               goto out;
+       }
+
+       /*
+        * Paranoia check. If we did not take the lock, then we should not be
+        * the owner, nor the pending owner, of the rt_mutex.
+        */
+       if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
+               printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
+                               "pi-state %p\n", ret,
+                               q->pi_state->pi_mutex.owner,
+                               q->pi_state->owner);
+
+out:
+       return ret ? ret : locked;
+}
+
+/**
  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
  * @hb:                the futex hash bucket, must be locked by the caller
  * @q:         the futex_q to queue up on
@@ -1459,11 +1532,10 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
                         int detect, ktime_t *time, int trylock)
 {
        struct hrtimer_sleeper timeout, *to = NULL;
-       struct task_struct *curr = current;
        struct futex_hash_bucket *hb;
        u32 uval;
        struct futex_q q;
-       int ret;
+       int res, ret;
 
        if (refill_pi_state_cache())
                return -ENOMEM;
@@ -1527,71 +1599,21 @@ retry_private:
        }
 
        spin_lock(q.lock_ptr);
-
-       if (!ret) {
-               /*
-                * Got the lock. We might not be the anticipated owner
-                * if we did a lock-steal - fix up the PI-state in
-                * that case:
-                */
-               if (q.pi_state->owner != curr)
-                       ret = fixup_pi_state_owner(uaddr, &q, curr, fshared);
-       } else {
-               /*
-                * Catch the rare case, where the lock was released
-                * when we were on the way back before we locked the
-                * hash bucket.
-                */
-               if (q.pi_state->owner == curr) {
-                       /*
-                        * Try to get the rt_mutex now. This might
-                        * fail as some other task acquired the
-                        * rt_mutex after we removed ourself from the
-                        * rt_mutex waiters list.
-                        */
-                       if (rt_mutex_trylock(&q.pi_state->pi_mutex))
-                               ret = 0;
-                       else {
-                               /*
-                                * pi_state is incorrect, some other
-                                * task did a lock steal and we
-                                * returned due to timeout or signal
-                                * without taking the rt_mutex. Too
-                                * late. We can access the
-                                * rt_mutex_owner without locking, as
-                                * the other task is now blocked on
-                                * the hash bucket lock. Fix the state
-                                * up.
-                                */
-                               struct task_struct *owner;
-                               int res;
-
-                               owner = rt_mutex_owner(&q.pi_state->pi_mutex);
-                               res = fixup_pi_state_owner(uaddr, &q, owner,
-                                                          fshared);
-
-                               /* propagate -EFAULT, if the fixup failed */
-                               if (res)
-                                       ret = res;
-                       }
-               } else {
-                       /*
-                        * Paranoia check. If we did not take the lock
-                        * in the trylock above, then we should not be
-                        * the owner of the rtmutex, neither the real
-                        * nor the pending one:
-                        */
-                       if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
-                               printk(KERN_ERR "futex_lock_pi: ret = %d "
-                                      "pi-mutex: %p pi-state %p\n", ret,
-                                      q.pi_state->pi_mutex.owner,
-                                      q.pi_state->owner);
-               }
-       }
+       /*
+        * Fixup the pi_state owner and possibly acquire the lock if we
+        * haven't already.
+        */
+       res = fixup_owner(uaddr, fshared, &q, !ret);
+       /*
+        * If fixup_owner() returned an error, proprogate that.  If it acquired
+        * the lock, clear our -ETIMEDOUT or -EINTR.
+        */
+       if (res)
+               ret = (res < 0) ? res : 0;
 
        /*
-        * If fixup_pi_state_owner() faulted and was unable to handle the
-        * fault, unlock it and return the fault to userspace.
+        * If fixup_owner() faulted and was unable to handle the fault, unlock
+        * it and return the fault to userspace.
         */
        if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
                rt_mutex_unlock(&q.pi_state->pi_mutex);
@@ -1599,9 +1621,7 @@ retry_private:
        /* Unqueue and drop the lock */
        unqueue_me_pi(&q);
 
-       if (to)
-               destroy_hrtimer_on_stack(&to->timer);
-       return ret != -EINTR ? ret : -ERESTARTNOINTR;
+       goto out;
 
 out_unlock_put_key:
        queue_unlock(&q, hb);
@@ -1611,7 +1631,7 @@ out_put_key:
 out:
        if (to)
                destroy_hrtimer_on_stack(&to->timer);
-       return ret;
+       return ret != -EINTR ? ret : -ERESTARTNOINTR;
 
 uaddr_faulted:
        /*