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Date:   Mon, 9 Apr 2018 15:09:38 -0700
From:   Tejun Heo <tj@kernel.org>
To:     Alexandru Moise <00moses.alexander00@gmail.com>
Cc:     axboe@kernel.dk, shli@fb.com, nborisov@suse.com, arnd@arndb.de,
        gregkh@linuxfoundation.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: [PATCH v2] blk-cgroup: remove entries in blkg_tree before queue
 release
Message-ID: <20180409220938.GI3126663@devbig577.frc2.facebook.com>
References: <20180407102148.GA9729@gmail.com>
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(cc'ing Joseph as he worked on the area recently, hi!)

Hello,

On Sat, Apr 07, 2018 at 12:21:48PM +0200, Alexandru Moise wrote:
> The q->id is used as an index within the blkg_tree radix tree.
> 
> If the entry is not released before reclaiming the blk_queue_ida's id
> blkcg_init_queue() within a different driver from which this id
> was originally for can fail due to the entry at that index within
> the radix tree already existing.
> 
> Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com>
> ---
> v2: Added no-op for !CONFIG_BLK_CGROUP
> 
>  block/blk-cgroup.c         | 2 +-
>  block/blk-sysfs.c          | 4 ++++
>  include/linux/blk-cgroup.h | 3 +++
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 1c16694ae145..224e937dbb59 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -369,7 +369,7 @@ static void blkg_destroy(struct blkcg_gq *blkg)
>   *
>   * Destroy all blkgs associated with @q.
>   */
> -static void blkg_destroy_all(struct request_queue *q)
> +void blkg_destroy_all(struct request_queue *q)
>  {
>  	struct blkcg_gq *blkg, *n;
>  
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index d00d1b0ec109..a72866458f22 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -816,6 +816,10 @@ static void __blk_release_queue(struct work_struct *work)
>  	if (q->bio_split)
>  		bioset_free(q->bio_split);
>  
> +	spin_lock_irq(q->queue_lock);
> +	blkg_destroy_all(q);
> +	spin_unlock_irq(q->queue_lock);
> +
>  	ida_simple_remove(&blk_queue_ida, q->id);
>  	call_rcu(&q->rcu_head, blk_free_queue_rcu);

But we already do this through calling blkcg_exit_queue() from
__blk_release_queue().  What's missing?

Thanks.

-- 
tejun