linux-kernel - Re: [4.10, panic, regression] iscsi: null pointer deref at iscsi_tcp_segment

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Date:   Sat, 24 Dec 2016 14:17:26 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Christoph Hellwig <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Chris Leech <cleech@...hat.com>, Ming Lei <tom.leiming@...il.com>,
        Dave Chinner <david@...morbit.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lee Duncan <lduncan@...e.com>, open-iscsi@...glegroups.com,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Jens Axboe <axboe@...com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [4.10, panic, regression] iscsi: null pointer deref at
 iscsi_tcp_segment_done+0x20d/0x2e0

On 12/24/2016 11:07 AM, Christoph Hellwig wrote:
> On Fri, Dec 23, 2016 at 11:42:45AM -0800, Linus Torvalds wrote:
>> Ugh. This patch is nasty.
>
> It's the same SCSI has done for ages - except that is uses a separate
> kmalloc for the sense buffer.
>
>> I think we should just fix blk_execute_rq() instead.
>
> As you found out below it's not just blk_execute_rq, it's the whole
> architecture of the BLOCK_PC code, which expects a caller provided
> sense buffer.  But with the way blk-mq allocates request structures
> we can actually fix it, but I first need to extent the way it allows
> drivers to allocate private data to the old request code.  I've
> actually already implemented that for SCSI long time ago, and have
> started to life it to the block layer.
>
Would be cool to have a generic sense buffer.
I always found it slightly odd, pretending that 'struct request' is 
protocol-agnostic and refusing to add a sense data pointer, but at the 
same time having a field 'sense_len' (which gives the length of what 
exactly?).

Christoph, do you have a pointer to your patchset?
Not that I'll be able to do any meaningful work until next year, but 
having a look would be nice. Just to get a feeling where you want to 
head to; I might be able to work on this start of January.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)