diff options
| author | Dennis Zhou (Facebook) <dennisszhou@gmail.com> | 2018-08-31 23:22:44 +0300 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-08-31 23:48:58 +0300 |
| commit | 3111885015b458c97b4cf272e2a87f1d6f0ed06a (patch) | |
| tree | 828379a8a4a92e45414f08b05a9e143d72e7d7ea | |
| parent | 59b57717fff8b562825d9d25e0180ad7e8048ca9 (diff) | |
| download | linux-3111885015b458c97b4cf272e2a87f1d6f0ed06a.tar.xz | |
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>
| -rw-r--r-- | block/bio.c | 3 | ||||
| -rw-r--r-- | block/blk-throttle.c | 5 |
2 files changed, 5 insertions, 3 deletions
diff --git a/block/bio.c b/block/bio.c index b12966e415d3..8c680a776171 100644 --- a/block/bio.c +++ b/block/bio.c @@ -2015,7 +2015,8 @@ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg) { if (unlikely(bio->bi_blkg)) return -EBUSY; - blkg_get(blkg); + if (!blkg_try_get(blkg)) + return -ENODEV; bio->bi_blkg = blkg; return 0; } diff --git a/block/blk-throttle.c b/block/blk-throttle.c index a3eede00d302..01d0620a4e4a 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -2129,8 +2129,9 @@ static inline void throtl_update_latency_buckets(struct throtl_data *td) static void blk_throtl_assoc_bio(struct throtl_grp *tg, struct bio *bio) { #ifdef CONFIG_BLK_DEV_THROTTLING_LOW - if (bio->bi_css) - bio_associate_blkg(bio, tg_to_blkg(tg)); + /* fallback to root_blkg if we fail to get a blkg ref */ + if (bio->bi_css && (bio_associate_blkg(bio, tg_to_blkg(tg)) == -ENODEV)) + bio_associate_blkg(bio, bio->bi_disk->queue->root_blkg); bio_issue_init(&bio->bi_issue, bio_sectors(bio)); #endif } |