---

yaml
---
r: 287907
b: refs/heads/master
c: 971316f
h: refs/heads/master
i:
  287905: 69eed9b
  287903: 2193b1e
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: d80e731ecab420ddcb79ee9d0ac427acbc187b4b
+refs/heads/master: 971316f0503a5c50633d07b83b6db2f15a3a5b00

trunk/fs/eventpoll.c

@@ -320,6 +320,11 @@ static inline int ep_is_linked(struct list_head *p)
 	return !list_empty(p);
 }
 
+static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_t *p)
+{
+	return container_of(p, struct eppoll_entry, wait);
+}
+
 /* Get the "struct epitem" from a wait queue pointer */
 static inline struct epitem *ep_item_from_wait(wait_queue_t *p)
 {
@@ -467,6 +472,18 @@ static void ep_poll_safewake(wait_queue_head_t *wq)
 	put_cpu();
 }
 
+static void ep_remove_wait_queue(struct eppoll_entry *pwq)
+{
+	wait_queue_head_t *whead;
+
+	rcu_read_lock();
+	/* If it is cleared by POLLFREE, it should be rcu-safe */
+	whead = rcu_dereference(pwq->whead);
+	if (whead)
+		remove_wait_queue(whead, &pwq->wait);
+	rcu_read_unlock();
+}
+
 /*
  * This function unregisters poll callbacks from the associated file
  * descriptor.  Must be called with "mtx" held (or "epmutex" if called from
@@ -481,7 +498,7 @@ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
 		pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
 
 		list_del(&pwq->llink);
-		remove_wait_queue(pwq->whead, &pwq->wait);
+		ep_remove_wait_queue(pwq);
 		kmem_cache_free(pwq_cache, pwq);
 	}
 }
@@ -842,9 +859,16 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
 	struct epitem *epi = ep_item_from_wait(wait);
 	struct eventpoll *ep = epi->ep;
 
-	/* the caller holds eppoll_entry->whead->lock */
-	if ((unsigned long)key & POLLFREE)
+	if ((unsigned long)key & POLLFREE) {
+		ep_pwq_from_wait(wait)->whead = NULL;
+		/*
+		 * whead = NULL above can race with ep_remove_wait_queue()
+		 * which can do another remove_wait_queue() after us, so we
+		 * can't use __remove_wait_queue(). whead->lock is held by
+		 * the caller.
+		 */
 		list_del_init(&wait->task_list);
+	}
 
 	spin_lock_irqsave(&ep->lock, flags);
 

trunk/fs/signalfd.c

@@ -33,7 +33,11 @@
 void signalfd_cleanup(struct sighand_struct *sighand)
 {
 	wait_queue_head_t *wqh = &sighand->signalfd_wqh;
-
+	/*
+	 * The lockless check can race with remove_wait_queue() in progress,
+	 * but in this case its caller should run under rcu_read_lock() and
+	 * sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return.
+	 */
 	if (likely(!waitqueue_active(wqh)))
 		return;