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From: Tejun Heo <tj@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	cgroups@vger.kernel.org, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH v5 3/3] blk-cgroup: Optimize blkcg_rstat_flush()
Date: Thu, 2 Jun 2022 06:58:52 -1000	[thread overview]
Message-ID: <YpjsTNZx4DG+kot4@slm.duckdns.org> (raw)
In-Reply-To: <20220602133543.128088-4-longman@redhat.com>

Hello,

On Thu, Jun 02, 2022 at 09:35:43AM -0400, Waiman Long wrote:
> @@ -2011,9 +2076,16 @@ void blk_cgroup_bio_start(struct bio *bio)
>  	}
>  	bis->cur.ios[rwd]++;
>  
> +	if (!READ_ONCE(bis->lnode.next)) {
> +		struct llist_head *lhead = per_cpu_ptr(blkcg->lhead, cpu);
> +
> +		llist_add(&bis->lnode, lhead);
> +		percpu_ref_get(&bis->blkg->refcnt);

Hmm... what guarantees that more than one threads race here? llist assumes
that there's a single writer for a given llist_node and the ref count would
be off too, right?

Thanks.

-- 
tejun

  reply	other threads:[~2022-06-02 16:59 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-01 21:18 [PATCH v3 0/2] blk-cgroup: Optimize blkcg_rstat_flush() Waiman Long
2022-06-01 21:18 ` Waiman Long
2022-06-01 21:18 ` [PATCH v3 1/2] blk-cgroup: Correctly free percpu iostat_cpu in blkg on error exit Waiman Long
2022-06-01 21:18 ` [PATCH v3 2/2] blk-cgroup: Optimize blkcg_rstat_flush() Waiman Long
2022-06-01 21:18   ` Waiman Long
2022-06-01 21:26   ` Tejun Heo
2022-06-01 21:30     ` Waiman Long
2022-06-02  6:32   ` kernel test robot
2022-06-02  1:54 ` [PATCH v4 " Waiman Long
2022-06-02  1:54   ` Waiman Long
2022-06-02 13:35 ` [PATCH v5 0/3] " Waiman Long
2022-06-02 13:35 ` [PATCH v5 1/3] blk-cgroup: Correctly free percpu iostat_cpu in blkg on error exit Waiman Long
2022-06-02 18:54   ` [PATCH v5 4/4] blk-cgroup: Document the design of new lockless iostat_cpu list Waiman Long
2022-06-02 18:54     ` Waiman Long
2022-06-02 19:05     ` Tejun Heo
2022-06-02 19:12       ` Waiman Long
2022-06-02 19:12         ` Waiman Long
2022-06-02 13:35 ` [PATCH v5 2/3] blk-cgroup: Return -ENOMEM directly in blkcg_css_alloc() error path Waiman Long
2022-06-02 13:35   ` Waiman Long
2022-06-02 16:16   ` Tejun Heo
2022-06-02 17:17     ` Waiman Long
2022-06-02 17:17       ` Waiman Long
2022-06-02 13:35 ` [PATCH v5 3/3] blk-cgroup: Optimize blkcg_rstat_flush() Waiman Long
2022-06-02 16:58   ` Tejun Heo [this message]
2022-06-02 17:26     ` Waiman Long
2022-06-02 17:26       ` Waiman Long
2022-06-02 17:46       ` Tejun Heo
2022-06-02 17:46         ` Tejun Heo
2022-06-02 18:18         ` Waiman Long
2022-06-02 18:18           ` Waiman Long

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