linux-kernel - Re: [PATCH v3] block: genhd: don't call probe function with major_names

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Date:   Tue, 17 Aug 2021 19:18:09 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Christoph Hellwig <hch@....de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>,
        linux-kernel@...r.kernel.org,
        linux-block <linux-block@...r.kernel.org>
Subject: Re: [PATCH v3] block: genhd: don't call probe function with
 major_names_lock held

On 2021/08/17 17:10, Hillf Danton wrote:
> See if it is safe to kfree(lo) after removing it from idr, with the
> deadlock dissolved.

It is not safe to call loop_remove() after idr_remove(). Please see HIDDEN_LOOP_DEVICE magic
in "[PATCH] loop: break loop_ctl_mutex into loop_idr_spinlock and loop_removal_mutex".

> 
> --- x/drivers/block/loop.c
> +++ y/drivers/block/loop.c
> @@ -2459,7 +2459,9 @@ static int loop_control_remove(int idx)
>  	mutex_unlock(&lo->lo_mutex);
>  
>  	idr_remove(&loop_index_idr, lo->lo_number);
> +	mutex_unlock(&loop_ctl_mutex);
>  	loop_remove(lo);
> +	return 0;
>  out_unlock_ctrl:
>  	mutex_unlock(&loop_ctl_mutex);
>  	return ret;
> --
> 

"[PATCH] loop: break loop_ctl_mutex into loop_idr_spinlock and loop_removal_mutex" can be a further
improvement after "[PATCH v3] block: genhd: don't call probe function with major_names_lock held".

I really would like to apply "[PATCH v3] block: genhd: don't call probe function with major_names_lock held" first.