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    SubjectRe: [PATCH]: Fix old SCSI adapter crashes with CD-ROM (take 2)
    On Tue, May 08 2007, Mike Christie wrote:
    > 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).
    > >
    > > 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
    > >
    >
    > Hey Jens and James, one thing I forgot to mention is that I could not
    > remember if I needed an extra bio_get in there. I thought I did not
    > because the caller is not touching the bio after the bio_endio calls
    > like is done with the blk/bio_map_user path. But I did that patch so
    > long ago I do not remember now.

    If you don't touch it after bio_endio(), then you don't need to hold an
    extra reference to it. I'll add your patch.

    --
    Jens Axboe

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