Re: dm: fix blk-mq request-based DM queue initialization

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Apr 30 2015 at  4:23am -0400,
Christoph Hellwig <hch@lst.de> wrote:

> On Thu, Apr 30, 2015 at 09:22:00AM +0200, Christoph Hellwig wrote:
> > Well - we're obviously trying to reinitialize it here and only error
> > out very low level with your patch.  What I mean is that we shouldn't
> > even try to reinitialize it at a much higher level, so we don't need
> > this blk-mq specific hack down here.

OK, understood.

> FYI, this fixes the isssue for me and seems to be "more correct" at
> a higher level:

Yeah, I like this.  Means the early return in
dm_init_request_based_queue() can be removed too.

> ---
> From: Christoph Hellwig <hch@lst.de>
> Subject: [PATCH] dm: only initialize request_queue once
> 
> We should only inіnitialize the request_queue on the initial table load when
> we assing the device type.

"assing" ;)  Will fix up and also add that this patch fixes the issue
you reported, thanks.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index c8a18e4..de92662 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -1298,21 +1298,22 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
>  		goto err_unlock_md_type;
>  	}
>  
> -	if (dm_get_md_type(md) == DM_TYPE_NONE)
> +	if (dm_get_md_type(md) == DM_TYPE_NONE) {
>  		/* Initial table load: acquire type of table. */
>  		dm_set_md_type(md, dm_table_get_type(t));
> -	else if (dm_get_md_type(md) != dm_table_get_type(t)) {
> +	
> +		/* setup md->queue to reflect md's type (may block) */
> +		r = dm_setup_md_queue(md);
> +		if (r) {
> +			DMWARN("unable to set up device queue for new table.");
> +			goto err_unlock_md_type;
> +		}
> +	} else if (dm_get_md_type(md) != dm_table_get_type(t)) {
>  		DMWARN("can't change device type after initial table load.");
>  		r = -EINVAL;
>  		goto err_unlock_md_type;
>  	}
>  
> -	/* setup md->queue to reflect md's type (may block) */
> -	r = dm_setup_md_queue(md);
> -	if (r) {
> -		DMWARN("unable to set up device queue for new table.");
> -		goto err_unlock_md_type;
> -	}
>  	dm_unlock_md_type(md);
>  
>  	/* stage inactive table */

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