diff options
| author | Dennis Zhou (Facebook) <dennisszhou@gmail.com> | 2018-09-11 14:41:26 -0400 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-09-21 20:29:02 -0600 |
| commit | 27e6fa996c534c32702aa4d32db0ffa383acd050 (patch) | |
| tree | fbeed4501b887851cc4b48af3ddb9d24d8e2dd9f /block/cfq-iosched.c | |
| parent | 9ff01255a01c3d6ffc8670b358b3ac567d5646fc (diff) | |
blkcg: fix ref count issue with bio_blkcg using task_css
The accessor function bio_blkcg either returns the blkcg associated with
the bio or finds one in the current context. This can cause an issue
when trying to associate a bio with a blkcg. Particularly, it's the
third case that is problematic:
return css_to_blkcg(task_css(current, io_cgrp_id));
As the above may race against task migration and the cgroup exiting, it
is not always ok to take a reference on the blkcg returned from
bio_blkcg.
This patch adds association ahead of calling bio_blkcg rather than
after. This makes association a required and explicit step along the
code paths for calling bio_blkcg. blk_get_rl is modified as well to get
a reference to the blkcg it may use and blk_put_rl will always put the
reference back. Association is also moved above the bio_blkcg call to
ensure it will not return NULL in blk-iolatency.
BFQ and CFQ utilize this flaw, but due to the complexity, I do not want
to address this in this series. I've created a private version of the
function with notes not to use it describing the flaw. Hopefully soon,
that code can be cleaned up.
Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/cfq-iosched.c')
| -rw-r--r-- | block/cfq-iosched.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 2eb87444b157..d219e9a1af65 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -3753,7 +3753,7 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) uint64_t serial_nr; rcu_read_lock(); - serial_nr = bio_blkcg(bio)->css.serial_nr; + serial_nr = __bio_blkcg(bio)->css.serial_nr; rcu_read_unlock(); /* @@ -3818,7 +3818,7 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic, struct cfq_group *cfqg; rcu_read_lock(); - cfqg = cfq_lookup_cfqg(cfqd, bio_blkcg(bio)); + cfqg = cfq_lookup_cfqg(cfqd, __bio_blkcg(bio)); if (!cfqg) { cfqq = &cfqd->oom_cfqq; goto out; |