Re: [PATCH 7/8] loop: only freeze the queue in __loop_clr_fd when needed

From: Jan Kara <jack@suse.cz>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Jan Kara <jack@suse.cz>,
	linux-block@vger.kernel.org, Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH 7/8] loop: only freeze the queue in __loop_clr_fd when needed
Date: Thu, 27 Jan 2022 12:01:43 +0100	[thread overview]
Message-ID: <20220127110143.g3jsi3z5vpxhotep@quack3.lan> (raw)
In-Reply-To: <20220126155040.1190842-8-hch@lst.de>

On Wed 26-01-22 16:50:39, Christoph Hellwig wrote:
> ->release is only called after all outstanding I/O has completed, so only
> freeze the queue when clearing the backing file of a live loop device.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good. I was just wondering: Is there anything which prevents us from
moving blk_mq_freeze_queue() & blk_mq_unfreeze_queue() calls to
loop_clr_fd() around __loop_clr_fd() call?

Anyway feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  drivers/block/loop.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index d9a0e2205762f..fc0cdd1612b1d 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1110,7 +1110,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
>  	return error;
>  }
>  
> -static void __loop_clr_fd(struct loop_device *lo)
> +static void __loop_clr_fd(struct loop_device *lo, bool release)
>  {
>  	struct file *filp;
>  	gfp_t gfp = lo->old_gfp_mask;
> @@ -1139,8 +1139,13 @@ static void __loop_clr_fd(struct loop_device *lo)
>  	if (test_bit(QUEUE_FLAG_WC, &lo->lo_queue->queue_flags))
>  		blk_queue_write_cache(lo->lo_queue, false, false);
>  
> -	/* freeze request queue during the transition */
> -	blk_mq_freeze_queue(lo->lo_queue);
> +	/*
> +	 * Freeze the request queue when unbinding on a live file descriptor and
> +	 * thus an open device.  When called from ->release we are guaranteed
> +	 * that there is no I/O in progress already.
> +	 */
> +	if (!release)
> +		blk_mq_freeze_queue(lo->lo_queue);
>  
>  	destroy_workqueue(lo->workqueue);
>  	loop_free_idle_workers(lo, true);
> @@ -1163,7 +1168,8 @@ static void __loop_clr_fd(struct loop_device *lo)
>  	/* let user-space know about this change */
>  	kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
>  	mapping_set_gfp_mask(filp->f_mapping, gfp);
> -	blk_mq_unfreeze_queue(lo->lo_queue);
> +	if (!release)
> +		blk_mq_unfreeze_queue(lo->lo_queue);
>  
>  	disk_force_media_change(lo->lo_disk, DISK_EVENT_MEDIA_CHANGE);
>  
> @@ -1201,7 +1207,7 @@ static void loop_rundown_workfn(struct work_struct *work)
>  	struct block_device *bdev = lo->lo_device;
>  	struct gendisk *disk = lo->lo_disk;
>  
> -	__loop_clr_fd(lo);
> +	__loop_clr_fd(lo, true);
>  	kobject_put(&bdev->bd_device.kobj);
>  	module_put(disk->fops->owner);
>  	loop_rundown_completed(lo);
> @@ -1247,7 +1253,7 @@ static int loop_clr_fd(struct loop_device *lo)
>  	lo->lo_state = Lo_rundown;
>  	mutex_unlock(&lo->lo_mutex);
>  
> -	__loop_clr_fd(lo);
> +	__loop_clr_fd(lo, false);
>  	loop_rundown_completed(lo);
>  	return 0;
>  }
> -- 
> 2.30.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR