Commit 216f7647 authored Jan 03, 2023 by Yu Kuai Committed by Jens Axboe Jan 15, 2023

block, bfq: switch 'bfqg->ref' to use atomic refcount apis



The updating of 'bfqg->ref' should be protected by 'bfqd->lock', however,
during code review, we found that bfq_pd_free() update 'bfqg->ref'
without holding the lock, which is problematic:

1) bfq_pd_free() triggered by removing cgroup is called asynchronously;
2) bfqq will grab bfqg reference, and exit bfqq will drop the reference,
which can concurrent with 1).

Unfortunately, 'bfqd->lock' can't be held here because 'bfqd' might already
be freed in bfq_pd_free(). Fix the problem by using atomic refcount apis.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230103084755.1256479-1-yukuai1@huaweicloud.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent ee16c404

block/bfq-cgroup.c

+3 −5

Original line number	Diff line number	Diff line
		@@ -316,14 +316,12 @@ struct bfq_group bfqq_group(struct bfq_queue bfqq)

		static void bfqg_get(struct bfq_group *bfqg)
		{
		bfqg->ref++;
		refcount_inc(&bfqg->ref);
		}

		static void bfqg_put(struct bfq_group *bfqg)
		{
		bfqg->ref--;

		if (bfqg->ref == 0)
		if (refcount_dec_and_test(&bfqg->ref))
		kfree(bfqg);
		}

		@@ -530,7 +528,7 @@ static struct blkg_policy_data bfq_pd_alloc(gfp_t gfp, struct request_queue q,
		}

		/* see comments in bfq_bic_update_cgroup for why refcounting */
		bfqg_get(bfqg);
		refcount_set(&bfqg->ref, 1);
		return &bfqg->pd;
		}

block/bfq-iosched.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -928,7 +928,7 @@ struct bfq_group {
		char blkg_path[128];

		/* reference counter (see comments in bfq_bic_update_cgroup) */
		int ref;
		refcount_t ref;
		/* Is bfq_group still online? */
		bool online;