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Subject: Re: [PATCH v2] block: Skip destroyed blkg when restart in
 blkg_destroy_all()
To:     Tao Su <tao1.su@linux.intel.com>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk,
        yukuai1@huaweicloud.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20230428045149.1310073-1-tao1.su@linux.intel.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <c007f189-8573-8390-4338-ae4c281ffbee@huaweicloud.com>
Date:   Fri, 28 Apr 2023 14:12:06 +0800
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Hi,

?? 2023/04/28 12:51, Tao Su д??:
> Kernel hang in blkg_destroy_all() when total blkg greater than
> BLKG_DESTROY_BATCH_SIZE, because of not removing destroyed blkg in
> blkg_list. So the size of blkg_list is same after destroying a
> batch of blkg, and the infinite 'restart' occurs.
> 
> Since blkg should stay on the queue list until blkg_free_workfn(),
> skip destroyed blkg when restart a new round, which will solve this
> kernel hang issue and satisfy the previous will to restart.

Please add a fix tag:

Fixes: f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from 
blkg_free_workfn() and blkcg_deactivate_policy()")
> 
> Reported-by: Xiangfei Ma <xiangfeix.ma@intel.com>
> Tested-by: Xiangfei Ma <xiangfeix.ma@intel.com>
> Tested-by: Farrah Chen <farrah.chen@intel.com>
> Signed-off-by: Yu Kuai <yukuai1@huaweicloud.com>

You can remove this tag, and feel free to add:

Suggested-and-reviewed-by: Yu Kuai <yukuai3@huawei.com>

Thanks,
Kuai
> Signed-off-by: Tao Su <tao1.su@linux.intel.com>
> ---
> v2:
> - change 'directly remove destroyed blkg' to 'skip destroyed blkg'
> 
> v1:
> - https://lore.kernel.org/all/20230425075911.839539-1-tao1.su@linux.intel.com/
> 
>   block/blk-cgroup.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index bd50b55bdb61..75bad5d60c9f 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -528,6 +528,9 @@ static void blkg_destroy_all(struct gendisk *disk)
>   	list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
>   		struct blkcg *blkcg = blkg->blkcg;
>   
> +		if (hlist_unhashed(&blkg->blkcg_node))
> +			continue;
> +
>   		spin_lock(&blkcg->lock);
>   		blkg_destroy(blkg);
>   		spin_unlock(&blkcg->lock);
>