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    SubjectRe: Timeout regression introduced by 242f9dcb8ba6f68fcd217a119a7648a4f69290e9
    On Tue, Oct 28 2008, Tejun Heo wrote:
    > Mike Anderson wrote:
    > > Tejun Heo <tj@kernel.org> wrote:
    > >> James Bottomley wrote:
    > >>> On Sun, 2008-10-26 at 18:46 +0900, Tejun Heo wrote:
    > >>>> Hello, Jens.
    > >>>>
    > >>>> Commit 242f9dcb8ba6f68fcd217a119a7648a4f69290e9 introduces a strange
    > >>>> regression for libata. The second timeout gives puts different
    > >>>> pointer from the issued command onto eh_cmd_q breaking libata EH
    > >>>> command matching which triggers WARN_ON() in ata_eh_finish() and hangs
    > >>>> command processing or causes oops later depending on circumstances.
    > >>>>
    > >>>> Here are logs with induced timeouts (patch attached). In commit
    > >>>> 242f9dcb8, the XXX messages for the second timeout shows different
    > >>>> scsi_cmd pointers for eh_cmd_q and qc->scmd which is initialized by
    > >>>> ata_scsi_qc_new() during command translation.
    > >>> I can't see a way we could be getting a different command passed in from
    > >>> the actual one, since the only way to lose the command from the request
    > >>> is to go through the command completion routines which free it (and end
    > >>> the request).
    > >> I have no idea either. It's something in the timeout logic because on
    > >> the issue path the scmd pointer is identical but on tiemout pointer
    > >> for another scmd is queued on eh_cmd_q, which doesn't make much sense.
    > >>
    > >
    > > I was trying to recreate this error using ata_ram wth v2.6.28-rc2.
    > > Currently I am not able to see this error on timeout recovery using this
    > > setup. Does IO load (or other factors) effect the error being seen?
    >
    > Not at all. That's the only write command I issued.

    It's all extremely puzzling. Any chance I could talk you into stuffing
    some debug printks in there to see what the hell is going on?

    --
    Jens Axboe



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