Patch "blk-mq: fix race between timeout and CPU hotplug" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

blk-mq: fix race between timeout and CPU hotplug

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
blk-mq-fix-race-between-timeout-and-cpu-hotplug.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ming Lei <[email protected]>
Date: Tue, 21 Apr 2015 10:00:19 +0800
Subject: blk-mq: fix race between timeout and CPU hotplug

From: Ming Lei <[email protected]>

commit f054b56c951bf1731ba7314a4c7f1cc0b2977cc9 upstream.

Firstly during CPU hotplug, even queue is freezed, timeout handler still may come and access hctx->tags, which may cause use after free, so this patch deactivates timeout handler inside CPU hotplug notifier.

Secondly, tags can be shared by more than one queues, so we have to check if the hctx has been unmapped, otherwise still use-after-free on tags can be triggered.

---
 block/blk-mq.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

@@ -675,8 +675,11 @@ static void blk_mq_rq_timer(unsigned lon
 		data.next = blk_rq_timeout(round_jiffies_up(data.next));
 		mod_timer(&q->timeout, data.next);
 	} else {
-		queue_for_each_hw_ctx(q, hctx, i)
-			blk_mq_tag_idle(hctx);
+		queue_for_each_hw_ctx(q, hctx, i) {
+			/* the hctx may be unmapped, so check it here */
+			if (blk_mq_hw_queue_mapped(hctx))
+				blk_mq_tag_idle(hctx);
+		}
 	}
 }
 

@@ -2075,9 +2078,16 @@ static int blk_mq_queue_reinit_notify(st
 	 */
 	list_for_each_entry(q, &all_q_list, all_q_node)
 		blk_mq_freeze_queue_start(q);
-	list_for_each_entry(q, &all_q_list, all_q_node)
+	list_for_each_entry(q, &all_q_list, all_q_node) {
 		blk_mq_freeze_queue_wait(q);
 
+		/*
+		 * timeout handler can't touch hw queue during the
+		 * reinitialization
+		 */
+		del_timer_sync(&q->timeout);
+	}
+
 	list_for_each_entry(q, &all_q_list, all_q_node)
 		blk_mq_queue_reinit(q);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/blk-mq-fix-race-between-timeout-and-cpu-hotplug.patch queue-4.0/blk-mq-fix-cpu-hotplug-handling.patch