blkcg: use tryget logic when associating a blkg with a bio
authorDennis Zhou (Facebook) <dennisszhou@gmail.com>
Fri, 31 Aug 2018 20:22:44 +0000 (16:22 -0400)
committerJens Axboe <axboe@kernel.dk>
Fri, 31 Aug 2018 20:48:58 +0000 (14:48 -0600)
commit3111885015b458c97b4cf272e2a87f1d6f0ed06a
tree828379a8a4a92e45414f08b05a9e143d72e7d7ea
parent59b57717fff8b562825d9d25e0180ad7e8048ca9
blkcg: use tryget logic when associating a blkg with a bio

There is a very small change a bio gets caught up in a really
unfortunate race between a task migration, cgroup exiting, and itself
trying to associate with a blkg. This is due to css offlining being
performed after the css->refcnt is killed which triggers removal of
blkgs that reach their blkg->refcnt of 0.

To avoid this, association with a blkg should use tryget and fallback to
using the root_blkg.

Fixes: 08e18eab0c579 ("block: add bi_blkg to the bio for cgroups")
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Cc: Jiufei Xue <jiufei.xue@linux.alibaba.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block/bio.c
block/blk-throttle.c