Date: Fri, 21 Jul 2017 18:43:43 +0200
From: Johannes Thumshirn <jthumshirn@suse.de>
To: Jason L Tibbitts III <tibbs@math.uh.edu>,
        Doug Gilbert <dgilbert@interlog.com>
Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        dvyukov@google.com, hare@suse.com, hch@lst.de,
        martin.petersen@oracle.com, jth@kernel.org
Subject: Re: [REGRESSION] 28676d869bbb (scsi: sg: check for valid direction
 before starting the request) breaks mtx tape library control
Message-ID: <20170721164343.GA4086@linux-x5ow.site>
References: <ufafudubmkd.fsf@epithumia.math.uh.edu>
 <20170718073747.GD4875@linux-x5ow.site>
 <ufak235abug.fsf@epithumia.math.uh.edu>
 <20170719070335.GC4151@linux-x5ow.site>
 <ufazic0974h.fsf@epithumia.math.uh.edu>
 <20170719083654.GE4151@linux-x5ow.site>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20170719083654.GE4151@linux-x5ow.site>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1428
Lines: 43

Doug,

On Wed, Jul 19, 2017 at 10:36:54AM +0200, Johannes Thumshirn wrote:
> On Wed, Jul 19, 2017 at 03:13:34AM -0500, Jason L Tibbitts III wrote:
> > [   46.304530] sg_is_valid_dxfer: dxfer_direction: -2, dxfer_len: 0
> 
> Ahh now I see the -2 (SG_DXFER_TO_DEV) is the crucial point here. It is 0 in
> your case.
> 
> This would "fix" it but I'm not generally sure it is _the_ solution:
> 
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 1e82d4128a84..b421ec81d775 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -764,7 +764,7 @@ static bool sg_is_valid_dxfer(sg_io_hdr_t *hp)
>  		return true;
>  	case SG_DXFER_TO_DEV:
>  	case SG_DXFER_TO_FROM_DEV:
> -		if (!hp->dxferp || hp->dxfer_len == 0)
> +		if (!hp->dxferp)
>  			return false;
>  		return true;
>  	case SG_DXFER_UNKNOWN:
> 
> Doug, what are the rules for SG_DXFER_TO_{FROM_}DEV? Apparently we can't
> be sure len > 0, can we rely on dxferp being present?

Any comments on this?

Jason, can you try the above? If it works and Doug doesn't respond, I'm
inclined yo submit this band aid.

Thanks,
	Johannes

-- 
Johannes Thumshirn                                          Storage
jthumshirn@suse.de                                +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 N?rnberg
GF: Felix Imend?rffer, Jane Smithard, Graham Norton
HRB 21284 (AG N?rnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850