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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>
This commit is contained in:
Yu Kuai 2023-01-03 16:47:55 +08:00 committed by Jens Axboe
parent ee16c404f9
commit 216f764716
2 changed files with 4 additions and 6 deletions
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8
block/bfq-cgroup.c
View File

@ -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;
}

2
block/bfq-iosched.h
View File

@ -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;