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Message-Id: <20221227031541.2595647-1-yukuai1@huaweicloud.com>
Date: Tue, 27 Dec 2022 11:15:41 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: jack@...e.cz, tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk,
paolo.valente@...aro.org
Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, yukuai3@...wei.com,
yukuai1@...weicloud.com, yi.zhang@...wei.com
Subject: [PATCH RFC] block, bfq: switch 'bfqg->ref' to use atomic refcount apis
From: Yu Kuai <yukuai3@...wei.com>
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 concurrenty 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@...wei.com>
---
block/bfq-cgroup.c | 8 +++-----
block/bfq-iosched.h | 2 +-
2 files changed, 4 insertions(+), 6 deletions(-)
diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 1b2829e99dad..aa9c4f02e3a3 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -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;
}
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 41aa151ccc22..466e4865ace6 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -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;
--
2.31.1
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