[PATCH 1/2] blkcg: fix edge case for blk_get_rl() under memory pressure

From: Dennis Zhou
Date: Sat Oct 20 2018 - 14:56:40 EST

It is possible for blkg creation to fail when in blk_get_rl(). In this
situation, the fallback logic returns the nearest created blkg. There is
however special handling for the request_list for the root blkcg. This
fixes the missing edge case from the earlier series changing

Fixes: e2b0989954ae ("blkcg: cleanup and make blk_get_rl use blkg_lookup_create")
Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx>
include/linux/blk-cgroup.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index b7fd08013de2..1e76ceebeb5d 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -597,7 +597,7 @@ static inline struct request_list *blk_get_rl(struct request_queue *q,
if (unlikely(!blkg))
blkg = __blkg_lookup_create(blkcg, q);

- if (!blkg_tryget(blkg))
+ if (blkg->blkcg == &blkcg_root || !blkg_tryget(blkg))
goto rl_use_root;