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authorDennis Zhou (Facebook) <dennisszhou@gmail.com>2018-09-11 14:41:26 -0400
committerJens Axboe <axboe@kernel.dk>2018-09-21 20:29:02 -0600
commit27e6fa996c534c32702aa4d32db0ffa383acd050 (patch)
treefbeed4501b887851cc4b48af3ddb9d24d8e2dd9f /block/blk-iolatency.c
parent9ff01255a01c3d6ffc8670b358b3ac567d5646fc (diff)
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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.c2
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)