linux-kernel - Re: [PATCH v2] blk-cgroup: remove entries in blkg

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Date:   Wed, 11 Apr 2018 23:23:20 +0200
From:   Alexandru Moise <00moses.alexander00@...il.com>
To:     Bart Van Assche <bart.vanassche@....com>
Cc:     "tj@...nel.org" <tj@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "nborisov@...e.com" <nborisov@...e.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>, "shli@...com" <shli@...com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "joseph.qi@...ux.alibaba.com" <joseph.qi@...ux.alibaba.com>,
        "arnd@...db.de" <arnd@...db.de>
Subject: Re: [PATCH v2] blk-cgroup: remove entries in blkg_tree before queue
 release

On Wed, Apr 11, 2018 at 01:55:25PM -0600, Bart Van Assche wrote:
> On 04/11/18 13:00, Alexandru Moise wrote:
> > But the root cause of it is in blkcg_init_queue() when blkg_create() returns
> > an ERR ptr, because it tries to insert into a populated index into blkcg->blkg_tree,
> > the entry that we fail to remove at __blk_release_queue().
> 
> Hello Alex,
> 
> Had you considered something like the untested patch below?
> 
> Thanks,
> 
> Bart.
> 
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 1c16694ae145..f2ced19e74b8 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -1191,14 +1191,17 @@ int blkcg_init_queue(struct request_queue *q)
>  	if (preloaded)
>  		radix_tree_preload_end();
> 
> -	if (IS_ERR(blkg))
> -		return PTR_ERR(blkg);
> +	if (IS_ERR(blkg)) {
> +		ret = PTR_ERR(blkg);
> +		goto destroy_all;
> +	}
> 
>  	q->root_blkg = blkg;
>  	q->root_rl.blkg = blkg;
> 
>  	ret = blk_throtl_init(q);
>  	if (ret) {
> +destroy_all:
>  		spin_lock_irq(q->queue_lock);
>  		blkg_destroy_all(q);
>  		spin_unlock_irq(q->queue_lock);
> 

Hi, I tested it, it doesn't solve the problem.
By the time you get here it's already too late, my patch
prevents this from failing in the first place.

I would have liked this more than my solution though.

../Alex