diff options
| author | Joseph Qi <joseph.qi@linux.alibaba.com> | 2018-03-16 14:51:27 +0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-03-16 10:35:12 -0600 |
| commit | 4c6994806f708559c2812b73501406e21ae5dcd0 (patch) | |
| tree | a559dc2d5afe1689c02c3f8058a782cfe3c21c89 /include/linux/blk-cgroup.h | |
| parent | 5f990d316085aca11b04dc0f63d6df5e508d73c7 (diff) | |
blk-throttle: fix race between blkcg_bio_issue_check() and cgroup_rmdir()
We've triggered a WARNING in blk_throtl_bio() when throttling writeback
io, which complains blkg->refcnt is already 0 when calling blkg_get(),
and then kernel crashes with invalid page request.
After investigating this issue, we've found it is caused by a race
between blkcg_bio_issue_check() and cgroup_rmdir(), which is described
below:
writeback kworker cgroup_rmdir
cgroup_destroy_locked
kill_css
css_killed_ref_fn
css_killed_work_fn
offline_css
blkcg_css_offline
blkcg_bio_issue_check
rcu_read_lock
blkg_lookup
spin_trylock(q->queue_lock)
blkg_destroy
spin_unlock(q->queue_lock)
blk_throtl_bio
spin_lock_irq(q->queue_lock)
...
spin_unlock_irq(q->queue_lock)
rcu_read_unlock
Since rcu can only prevent blkg from releasing when it is being used,
the blkg->refcnt can be decreased to 0 during blkg_destroy() and schedule
blkg release.
Then trying to blkg_get() in blk_throtl_bio() will complains the WARNING.
And then the corresponding blkg_put() will schedule blkg release again,
which result in double free.
This race is introduced by commit ae1188963611 ("blkcg: consolidate blkg
creation in blkcg_bio_issue_check()"). Before this commit, it will
lookup first and then try to lookup/create again with queue_lock. Since
revive this logic is a bit drastic, so fix it by only offlining pd during
blkcg_css_offline(), and move the rest destruction (especially
blkg_put()) into blkcg_css_free(), which should be the right way as
discussed.
Fixes: ae1188963611 ("blkcg: consolidate blkg creation in blkcg_bio_issue_check()")
Reported-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/linux/blk-cgroup.h')
| -rw-r--r-- | include/linux/blk-cgroup.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 69bea82ebeb1..6c666fd7de3c 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -88,6 +88,7 @@ struct blkg_policy_data { /* the blkg and policy id this per-policy data belongs to */ struct blkcg_gq *blkg; int plid; + bool offline; }; /* |