linux-kernel - Re: [PATCH] target: fix crash in cmd tracing when cmd didn't match a LUN

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Date:	Fri, 24 Jul 2015 13:32:14 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Christoph Hellwig <hch@....de>
Cc:	Spencer Baugh <sbaugh@...ern.com>,
	Sagi Grimberg <sagig@...lanox.com>,
	Bart Van Assche <bart.vanassche@...disk.com>,
	Alexei Potashnik <alexei@...estorage.com>,
	Andy Grover <agrover@...hat.com>,
	Christophe Vu-Brugier <cvubrugier@...tmail.fm>,
	Roland Dreier <roland@...estorage.com>,
	"open list:TARGET SUBSYSTEM" <linux-scsi@...r.kernel.org>,
	"open list:TARGET SUBSYSTEM" <target-devel@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	Joern Engel <joern@...estorage.com>,
	Spencer Baugh <Spencer.baugh@...estorage.com>
Subject: Re: [PATCH] target: fix crash in cmd tracing when cmd didn't match
 a LUN

On Fri, 2015-07-24 at 12:52 +0200, Christoph Hellwig wrote:
> On Thu, Jul 23, 2015 at 03:19:32PM -0700, Spencer Baugh wrote:
> > From: Alexei Potashnik <alexei@...estorage.com>
> > 
> > If command didn't match a LUN and we're sending check condition, the
> > target_cmd_complete ftrace point will crash because it assumes that
> > cmd->t_task_cdb has been set.
> > 
> > The fix will temporarily set t_task_cdb to the se_cmd buffer
> > and copy first 6 bytes of cdb in there as soon as possible.
> > At a later point t_task_cdb is reset to the correct buffer,
> > but until then traces and printks don't cause a crash.
> 
> This is too ugly to live.  Just dropping the t_task_cdb dereference
> from the trace point sounds like the simples quick fix for now,

Yes, that is what I'd prefer as well.

> and removing the crazy layering violation in iSCSI that opencode
> target_submit_cmd is the proper long term fix.

We've already been through this discussion a couple of years back when
target_submit_cmd() first came into existence.

The reason iscsi/iser-target continues to be a special case is due to
immediate data vs. non immediate data and their respective command
sequence number ordering requirements.

--nab

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