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    SubjectRe: one-line-patch against SCSI-Read-Error-BUG()
    On Tue, Feb 05 2002, Ralf Oehler wrote:
    > Hi, List
    > I think, I found a very simple solution for this annoying BUG().

    You fail to understand that the BUG triggering indicates that their is a
    BUG _somewhere_ -- the triggered BUG is not the bug itself, of course,
    that would be stupid :-)

    > Since at least kernel 2.4.16 there is a BUG() in pci.h,
    > that crashes the kernel on any attempt to read a SCSI-Sector
    > from an erased MO-Medium and on any attempt to read
    > a sector from a SCSI-disk, which returns "Read-Error".
    > There seems to be a thinko in the corresponding code, which
    > does not take into account the case where a SCSI-READ
    > does not return any data because of a "sense code: read error"
    > or a "sense code: blank sector".
    > I simply commented out this BUG() statement (see below)
    > and everything worked well from there on. The BUG()
    > seems to be inadequate.

    The BUG is dangerous, because it means mapping DMA to a 0 address (plus
    offset). Naturally there is no way in hell your "fix" will be applied,
    since it a pretty bad bandaid.

    A safer solution for you right now would be to just terminate the
    mapping when you encounter this. So something ala

    if (!sg[i].page && !sg[i].address)
    return i;

    That's not a bug fix either, but at least it's safer than your version.
    Stock kernel won't be patched until the real problem is found, though.

    Jens Axboe

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