blkcg: fix edge case for blk_get_rl() under memory pressure
authorDennis Zhou <dennis@kernel.org>
Sat, 20 Oct 2018 18:56:11 +0000 (14:56 -0400)
committerJens Axboe <axboe@kernel.dk>
Sat, 20 Oct 2018 21:39:54 +0000 (15:39 -0600)
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
blk_get_rl().

Fixes: e2b0989954ae ("blkcg: cleanup and make blk_get_rl use blkg_lookup_create")
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
include/linux/blk-cgroup.h

index b7fd08013de281b3bd387373424456ba5fa8369c..1e76ceebeb5dc58c7f98e9f1d18d65fbe62477ef 100644 (file)
@@ -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 (unlikely(!blkg))
                blkg = __blkg_lookup_create(blkcg, q);
 
-       if (!blkg_tryget(blkg))
+       if (blkg->blkcg == &blkcg_root || !blkg_tryget(blkg))
                goto rl_use_root;
 
        rcu_read_unlock();
                goto rl_use_root;
 
        rcu_read_unlock();