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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/cfq-iosched.c
parent9ff01255a01c3d6ffc8670b358b3ac567d5646fc (diff)
downloadlinux-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/cfq-iosched.c')
-rw-r--r--block/cfq-iosched.c4
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;