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    SubjectRe: [PATCH]: Fix old SCSI adapter crashes with CD-ROM (take 2)
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    On Tue, 2007-05-08 at 18:40 +0200, Jens Axboe wrote:
    > 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@redhat.com>
    > > >
    > > > Signed-off-by: Jens Axboe <jens.axboe@oracle.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.

    It won't? I thought the issue (from the fix) is that cgc->buffer is
    outside of the device accessibility mask. The scsi_execute path
    allocates a request and then calls blk_rq_map_kern on the buffer (in
    this case cgc->buffer) ... the problem is that blk_rq_map_kern() doesn't
    currently bounce the buffer, but if it did (which is the functionality
    Mike's patch adds), surely the need to bounce it in the ioctl path would
    go away?

    James


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