Re: [PATCH V2 05/13] block: only account passthrough IO from userspace

From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-scsi@vger.kernel.org
Subject: Re: [PATCH V2 05/13] block: only account passthrough IO from userspace
Date: Tue, 25 Jan 2022 07:16:34 +0100	[thread overview]
Message-ID: <20220125061634.GA26495@lst.de> (raw)
In-Reply-To: <Ye8xleeYZfmwA3D7@T590>

On Tue, Jan 25, 2022 at 07:09:09AM +0800, Ming Lei wrote:
> > Please explain why you want to change this.
> 
> Please see the following code:

This needs to go into the commit log.

> 
>         /* passthrough requests can hold bios that do not have ->bi_bdev set */
>         if (rq->bio && rq->bio->bi_bdev)
>                 rq->part = rq->bio->bi_bdev;
>         else if (rq->q->disk)
>                 rq->part = rq->q->disk->part0;
> 
> q->disk can be cleared by disk_release() just when referring the above line, then
> NULL ptr reference is caused, and similar issue with any reference to rq->part for
> passthrough request sent not from userspace.

So why not key off accouning off "rq->bio && rq->bio->bi_bdev"
and remove the need for the flag and the second half of the assignment
above?  That is much less error probe and removes code size.