From 65c77fd9e8a1c8c3da0bbbea6b7efa3d6ef265f8 Mon Sep 17 00:00:00 2001
From: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Date: Mon, 22 Oct 2012 10:15:37 +0900
Subject: [PATCH] blkcg: stop iteration early if root_rl is the only request
list
__blk_queue_next_rl() finds next request list based on blkg_list
while skipping root_blkg in the list.
OTOH, root_rl is special as it may exist even without root_blkg.
Though the later part of the function handles such a case correctly,
exiting early is good for readability of the code.
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
block/blk-cgroup.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 3ad5e3fbf579e..d0b770391ad40 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -333,6 +333,9 @@ struct request_list *__blk_queue_next_rl(struct request_list *rl,
*/
if (rl == &q->root_rl) {
ent = &q->blkg_list;
+ /* There are no more block groups, hence no request lists */
+ if (list_empty(ent))
+ return NULL;
} else {
blkg = container_of(rl, struct blkcg_gq, rl);
ent = &blkg->q_node;
--
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