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| 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/blk-iolatency.c | |
| parent | 9ff01255a01c3d6ffc8670b358b3ac567d5646fc (diff) | |
| download | linux-27e6fa996c534c32702aa4d32db0ffa383acd050.tar.bz2 | |
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/blk-iolatency.c')
| -rw-r--r-- | block/blk-iolatency.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index a6f21527e6c7..82450c37f2aa 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -401,8 +401,8 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio, return; rcu_read_lock(); + bio_associate_blkcg(bio, NULL); blkcg = bio_blkcg(bio); - bio_associate_blkcg(bio, &blkcg->css); blkg = blkg_lookup(blkcg, q); if (unlikely(!blkg)) { if (!lock) |