mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-07-22 02:17:36 -04:00
Code Issues Packages Projects Releases Wiki Activity

blk-cgroup: don't nest queue_lock under blkcg->lock in blkcg_destroy_blkgs()

Browse Source 
The correct lock order is q->queue_lock before blkcg->lock, and in order
to prevent deadlock from blkcg_destroy_blkgs(), trylock is used for
q->queue_lock while blkcg->lock is already held, this is hacky.

Refactor blkcg_destroy_blkgs() to hold blkcg->lock only long enough to
get the first blkg and then release it. Then take q->queue_lock and
blkcg->lock in the correct order to destroy the blkg. This is a very cold
path, so the extra lock/unlock cycles are acceptable.

Also prepare to convert protecting blkcg with blkcg_mutex instead of
queue_lock.

Signed-off-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/00b03cf74a9937cb4d6dd67a189ddc00a3de0451.1780621988.git.yukuai@fygo.io
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai
2026-06-08 11:42:47 +08:00
committed by Jens Axboe
parent 457d3c4f0f
commit 4cfd7c1cff
1 changed files with 26 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

45
block/blk-cgroup.c
View File

@@ -1239,6 +1239,21 @@ struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css)
* This finally frees the blkcg.
*/
static struct blkcg_gq *blkcg_get_first_blkg(struct blkcg *blkcg)
{
struct blkcg_gq *blkg = NULL;
spin_lock_irq(&blkcg->lock);
if (!hlist_empty(&blkcg->blkg_list)) {
blkg = hlist_entry(blkcg->blkg_list.first, struct blkcg_gq,
blkcg_node);
blkg_get(blkg);
}
spin_unlock_irq(&blkcg->lock);
return blkg;
}
/**
* blkcg_destroy_blkgs - responsible for shooting down blkgs
* @blkcg: blkcg of interest
@@ -1252,32 +1267,24 @@ struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css)
*/
static void blkcg_destroy_blkgs(struct blkcg *blkcg)
{
struct blkcg_gq *blkg;
might_sleep();
spin_lock_irq(&blkcg->lock);
while (!hlist_empty(&blkcg->blkg_list)) {
struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
struct blkcg_gq, blkcg_node);
while ((blkg = blkcg_get_first_blkg(blkcg))) {
struct request_queue *q = blkg->q;
if (need_resched() || !spin_trylock(&q->queue_lock)) {
/*
* Given that the system can accumulate a huge number
* of blkgs in pathological cases, check to see if we
* need to rescheduling to avoid softlockup.
*/
spin_unlock_irq(&blkcg->lock);
cond_resched();
spin_lock_irq(&blkcg->lock);
continue;
}
spin_lock_irq(&q->queue_lock);
spin_lock(&blkcg->lock);
blkg_destroy(blkg);
spin_unlock(&q->queue_lock);
}
spin_unlock_irq(&blkcg->lock);
spin_unlock(&blkcg->lock);
spin_unlock_irq(&q->queue_lock);
blkg_put(blkg);
cond_resched();
}
}
/**