linux-kernel - Re: SCSI breakage on non-cache coherent architectures

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Message-Id: <1195501984.6970.1.camel@pasglop>
Date:	Tue, 20 Nov 2007 06:53:04 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Russell King <rmk@....linux.org.uk>
Subject: Re: SCSI breakage on non-cache coherent architectures


On Mon, 2007-11-19 at 05:32 -0700, Matthew Wilcox wrote:
> On Mon, Nov 19, 2007 at 04:35:23PM +1100, Benjamin Herrenschmidt wrote:
> > The other one I'm hitting now is that the SCSI layer nowadays embeds the
> 
> 'nowadays'?  It has always been so.

Wasn't it kmalloc'ed at one point ?

> > sense_buffer inside the scsi_cmnd structure without any kind of
> > alignment whatsoever. I've been hitting irregulary is a crash on SCSI command
> > completion that seems to be related to corruption of the "request"
> > pointer in struct scsi_cmnd and I think it might be the cause.
> > I'm now trying to setup a proper repro-case.
> 
> What other drivers do is DMA to their own allocation and then memcpy to
> the sense buffer.

What "other drivers" ? Those architectures use the same drivers as
everything else.

> There is a movement to allocate the sense data as its own sg list, but
> I don't think that patch has even been posted yet.

I've seen code creating an sglist from the scsi_cmnd->sense_buffer and
passing that to drivers. That breaks.

Ben.

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