From 3b627a3f934c493ada71217f14681e5157e95783 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Tue, 24 Nov 2015 15:58:53 -0700
Subject: [PATCH] block: clarify blk_add_timer() use case for blk-mq
Just a comment update on not needing queue_lock, and that we aren't
really adding the request to a timeout list for !mq.
Signed-off-by: Jens Axboe <axboe@fb.com>
---
block/blk-timeout.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index aa40aa93381b6..3610af5617488 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -186,6 +186,7 @@ unsigned long blk_rq_timeout(unsigned long timeout)
* Notes:
* Each request has its own timer, and as it is added to the queue, we
* set up the timer. When the request completes, we cancel the timer.
+ * Queue lock must be held for the non-mq case, mq case doesn't care.
*/
void blk_add_timer(struct request *req)
{
@@ -209,6 +210,11 @@ void blk_add_timer(struct request *req)
req->timeout = q->rq_timeout;
req->deadline = jiffies + req->timeout;
+
+ /*
+ * Only the non-mq case needs to add the request to a protected list.
+ * For the mq case we simply scan the tag map.
+ */
if (!q->mq_ops)
list_add_tail(&req->timeout_list, &req->q->timeout_list);
--
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