Commit d7c0aef0 authored by Yu Kuai's avatar Yu Kuai Committed by Zheng Zengkai
Browse files

blk-cgroup: prevent rcu_sched detected stalls warnings while iterating blkgs 

mainline inclusion
from mainline-v5.14-rc1
commit a731763f
category: bugfix
bugzilla: 185790 https://gitee.com/openeuler/kernel/issues/I4DDEL
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a731763fc479a9c64456e0643d0ccf64203100c9



---------------------------

We run a test that create millions of cgroups and blkgs, and then trigger
blkg_destroy_all(). blkg_destroy_all() will hold spin lock for a long
time in such situation. Thus release the lock when a batch of blkgs are
destroyed.

blkcg_activate_policy() and blkcg_deactivate_policy() might have the
same problem, however, as they are basically only called from module
init/exit paths, let's leave them alone for now.

Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20210707015649.1929797-1-yukuai3@huawei.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Reviewed-by: default avatarYufen Yu <yuyufen@huawei.com>
Reviewed-by: default avatarHou Tao <houtao1@huawei.com>

Signed-off-by: default avatarChen Jun <chenjun102@huawei.com>
Signed-off-by: default avatarZheng Zengkai <zhengzengkai@huawei.com>
parent c9b0ad23

block/blk-cgroup.c

+15 −0
Original line number Diff line number Diff line
@@ -57,6 +57,8 @@ static LIST_HEAD(all_blkcgs); /* protected by blkcg_pol_mutex */ 
bool blkcg_debug_stats = false;

static struct workqueue_struct *blkcg_punt_bio_wq;



#define BLKG_DESTROY_BATCH_SIZE  64



static bool blkcg_policy_enabled(struct request_queue *q,

				 const struct blkcg_policy *pol)

{
@@ -423,7 +425,9 @@ static void blkg_destroy(struct blkcg_gq *blkg) 
static void blkg_destroy_all(struct request_queue *q)

{

	struct blkcg_gq *blkg, *n;

	int count = BLKG_DESTROY_BATCH_SIZE;



restart:

	spin_lock_irq(&q->queue_lock);

	list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {

		struct blkcg *blkcg = blkg->blkcg;
@@ -431,6 +435,17 @@ static void blkg_destroy_all(struct request_queue *q) 
		spin_lock(&blkcg->lock);

		blkg_destroy(blkg);

		spin_unlock(&blkcg->lock);



		/*

		 * in order to avoid holding the spin lock for too long, release

		 * it when a batch of blkgs are destroyed.

		 */

		if (!(--count)) {

			count = BLKG_DESTROY_BATCH_SIZE;

			spin_unlock_irq(&q->queue_lock);

			cond_resched();

			goto restart;

		}

	}



	q->root_blkg = NULL;