linux-kernel - Re: [patch] nbd: blk_mq_init_queue returns an error code on failure, not NULL

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Message-ID: <20170109202707.GA29762@vader.DHCP.thefacebook.com>
Date:   Mon, 9 Jan 2017 12:27:07 -0800
From:   Omar Sandoval <osandov@...ndov.com>
To:     Jeff Moyer <jmoyer@...hat.com>
Cc:     axboe@...nel.dk, Markus Pargmann <mpa@...gutronix.de>,
        linux-block@...r.kernel.org, nbd-general@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Josef Bacik <jbacik@...com>
Subject: Re: [patch] nbd: blk_mq_init_queue returns an error code on failure,
 not NULL

On Mon, Jan 09, 2017 at 03:20:31PM -0500, Jeff Moyer wrote:
> Additionally, don't assign directly to disk->queue, otherwise
> blk_put_queue (called via put_disk) will choke (panic) on the errno
> stored there.
> 
> Bug found by code inspection after Omar found a similar issue in
> virtio_blk.  Compile-tested only.
> 
> Signed-off-by: Jeff Moyer <jmoyer@...hat.com>

Reviewed-by: Omar Sandoval <osandov@...com>

Compile-reviewed only :) Josef can probably test it if he cares enough,
but it looks right.

> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 38c576f..50a2020 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1042,6 +1042,7 @@ static int __init nbd_init(void)
>  		return -ENOMEM;
>  
>  	for (i = 0; i < nbds_max; i++) {
> +		struct request_queue *q;
>  		struct gendisk *disk = alloc_disk(1 << part_shift);
>  		if (!disk)
>  			goto out;
> @@ -1067,12 +1068,13 @@ static int __init nbd_init(void)
>  		 * every gendisk to have its very own request_queue struct.
>  		 * These structs are big so we dynamically allocate them.
>  		 */
> -		disk->queue = blk_mq_init_queue(&nbd_dev[i].tag_set);
> -		if (!disk->queue) {
> +		q = blk_mq_init_queue(&nbd_dev[i].tag_set);
> +		if (IS_ERR(q)) {
>  			blk_mq_free_tag_set(&nbd_dev[i].tag_set);
>  			put_disk(disk);
>  			goto out;
>  		}
> +		disk->queue = q;
>  
>  		/*
>  		 * Tell the block layer that we are not a rotational device