linux-kernel - Re: [PATCH]: Fix old SCSI adapter crashes with CD-ROM (take 2)

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Message-ID: <20070508164059.GD4163@kernel.dk>
Date:	Tue, 8 May 2007 18:40:59 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	James Bottomley <James.Bottomley@...elEye.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-scsi@...r.kernel.org,
	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH]: Fix old SCSI adapter crashes with CD-ROM (take 2)

On Tue, May 08 2007, James Bottomley wrote:
> On Tue, 2007-05-08 at 18:14 +0200, Jens Axboe wrote:
> > On Tue, May 08 2007, Alan Cox wrote:
> > > The CD-ROM layer doesn't bounce requests for old ISA controllers (and
> > > nor should it). However they get injected into the SCSI layer via
> > > sr_ioctl which also doesn't bounce them and SCSI then passes the buffer
> > > along to a device with unchecked_isa_dma set which either panics or
> > > truncates the buffer to 24bits.
> > > 
> > > According to Jens the right long term fix is for the CD layer to route
> > > the requests differently but in the mean time this has been tested by a
> > > victim and verified to sort the problem out. For the other 99.9% of users
> > > it's a no-op and doesn't bounce data.
> > > 
> > > Signed-off-by: Alan Cox <alan@...hat.com>
> > 
> > Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> > 
> > Christoph passed me his patch to get rid of ->generic_packet() in the
> > cdrom layer, so the work is almost complete. This patch is fine as a
> > work-around until that gets merged, though.
> 
> Actually, I think the new scsi request infrastructure should be doing
> the bouncing (rather than have it done in each problem path we
> discover).

Of course, bouncing should only be done in one layer (the block layer).
>
> Mike Christie tells me we're missing bouncing by accident in the
> scsi_execute path (but not the scsi_execute_async path).  He says this
> is the fix he proposed:
> 
> http://marc.info/?l=linux-scsi&m=115981479822790&w=2
> 
> Can we just merge this instead?

That's another issue. The problem here are requests (cgc's) initiated by
the cdrom.c layer. Those _should_ get mapped to a request and put on the
queue for the device, and thus get bounced by the block layer if
appropriate.

Mike's fix looks legit and should be merged as well, but it wont fix
this issue.

-- 
Jens Axboe

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