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Date: Fri, 26 Sep 2003 14:26:46 +0200
From: Jens Axboe <axboe@suse.de>
To: Matthew Wilcox <willy@debian.org>
Cc: Steven Dake <sdake@mvista.com>, linux-scsi@vger.kernel.org,
       linux-kernel@vger.kernel.org
Subject: Re: kernel BUG using multipath on 2.6.0-test5
Message-ID: <20030926122646.GA15415@suse.de>
References: <1064541435.4763.51.camel@persist.az.mvista.com> <20030926121703.GG24824@parcelfarce.linux.theplanet.co.uk>
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On Fri, Sep 26 2003, Matthew Wilcox wrote:
> On Thu, Sep 25, 2003 at 06:57:15PM -0700, Steven Dake wrote:
> > kernel BUG at drivers/scsi/scsi_lib.c:544!
> 
>         BUG_ON(!cmd->use_sg);
> 
> >  [<c01f631d>] scsi_init_io+0x7a/0x13d
> 
> static int scsi_init_io(struct scsi_cmnd *cmd)
>         struct request     *req = cmd->request;
>         cmd->use_sg = req->nr_phys_segments;
>         sgpnt = scsi_alloc_sgtable(cmd, GFP_ATOMIC);
> 
> >  [<c01f6455>] scsi_prep_fn+0x75/0x171
> 
> static int scsi_prep_fn(struct request_queue *q, struct request *req)
>         struct scsi_cmnd *cmd;
>         cmd->request = req;
>         ret = scsi_init_io(cmd);
> 
> .. this is getting outside my area of confidence.  Ask axboe why we might
> get a zero nr_phys_segments request passed in.

Looks like an mp bug. I'd suggest adding something ala

	if (!rq->nr_phys_segments || !rq->nr_hw_segments) {
		blk_dump_rq_flags(req, "scsi_init_io");
		return BLKPREP_KILL;
	}

inside the first

	} else if (req->flags & (REQ_CMD | REQ_BLOCK_PC)) {

drivers/scsi/scsi_lib.c:scsi_prep_fn(). That will show the state of such
a buggy request. I'm pretty sure this is an mp bug though.

-- 
Jens Axboe

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