1 files changed, 29 insertions, 15 deletions

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index b2009650afc2..5f477501bb3d 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4765,6 +4765,8 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
  */
 void bfq_put_queue(struct bfq_queue *bfqq)
 {
+	struct bfq_queue *item;
+	struct hlist_node *n;
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 	struct bfq_group *bfqg = bfqq_group(bfqq);
 #endif
@@ -4809,6 +4811,33 @@ void bfq_put_queue(struct bfq_queue *bfqq)
 			bfqq->bfqd->burst_size--;
 	}
 
+	/*
+	 * bfqq does not exist any longer, so it cannot be woken by
+	 * any other queue, and cannot wake any other queue. Then bfqq
+	 * must be removed from the woken list of its possible waker
+	 * queue, and all queues in the woken list of bfqq must stop
+	 * having a waker queue. Strictly speaking, these updates
+	 * should be performed when bfqq remains with no I/O source
+	 * attached to it, which happens before bfqq gets freed. In
+	 * particular, this happens when the last process associated
+	 * with bfqq exits or gets associated with a different
+	 * queue. However, both events lead to bfqq being freed soon,
+	 * and dangling references would come out only after bfqq gets
+	 * freed. So these updates are done here, as a simple and safe
+	 * way to handle all cases.
+	 */
+	/* remove bfqq from woken list */
+	if (!hlist_unhashed(&bfqq->woken_list_node))
+		hlist_del_init(&bfqq->woken_list_node);
+
+	/* reset waker for all queues in woken list */
+	hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
+				  woken_list_node) {
+		item->waker_bfqq = NULL;
+		bfq_clear_bfqq_has_waker(item);
+		hlist_del_init(&item->woken_list_node);
+	}
+
 	if (bfqq->bfqd && bfqq->bfqd->last_completed_rq_bfqq == bfqq)
 		bfqq->bfqd->last_completed_rq_bfqq = NULL;
 
@@ -4839,9 +4868,6 @@ static void bfq_put_cooperator(struct bfq_queue *bfqq)
 
 static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 {
-	struct bfq_queue *item;
-	struct hlist_node *n;
-
 	if (bfqq == bfqd->in_service_queue) {
 		__bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT);
 		bfq_schedule_dispatch(bfqd);
@@ -4851,18 +4877,6 @@ static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 
 	bfq_put_cooperator(bfqq);
 
-	/* remove bfqq from woken list */
-	if (!hlist_unhashed(&bfqq->woken_list_node))
-		hlist_del_init(&bfqq->woken_list_node);
-
-	/* reset waker for all queues in woken list */
-	hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
-				  woken_list_node) {
-		item->waker_bfqq = NULL;
-		bfq_clear_bfqq_has_waker(item);
-		hlist_del_init(&item->woken_list_node);
-	}
-
 	bfq_put_queue(bfqq); /* release process reference */
 }