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    SubjectRe: [BUG] ide dma_timer_expiry, then hard lockup
    Hello.

    Linas Vepstas wrote:

    >>Stuart_Hayes@Dell.com wrote:

    >>>I think reading the IDE status register clears the interrupt in the IDE
    >>>device, which might be causing the drive to think it's OK to generate
    >>>another interrupt.

    >> This is not how IDE drives are supposed to act -- they won't proceed any
    >>further until "interrupt pending" condition is cleared, so these aren't
    >>supposed to be "stacked". This behavior however is not strictly specified
    >>by ATA standards IIRC, but I can't readily imagine such situaltion anyway
    >>unless tagged command queueing (which is not supported by IDE core) and/or
    >>ATAPI command overlapping is in action...

    > The problem only manifests during high io load; perhaps a missing mutex
    > somewhere is blasting one thing too many out to the hard drive?

    Hm... not sure about this.

    >>>This could either cause it to get stuck trying to
    >>>service an interrupt that is never getting cleared as you suggested, or
    >>>possibly when the next IRQ comes in the IDE IRQ handler gets stuck
    >>>waiting for a spinlock that the code you're looking at already owns...?

    >> I could also imagine the HPT366 chip going mad and stalling the reads if
    >>the taskfile regs forever because of the incomplete DMA or even the drive
    >>going mad and not replying to I/O cycles with proper -IORDY handshake (i.e.
    >>holding it low all the time)...

    > In my case, ctrl-alt-sysrq doesn't work, which makes it hard to debug.

    > I'm thinking that trying to debug libata is a better idea, rather than
    > investing time in ide, right? Although at the moment, libata works even
    > less; see other email.

    Which makes me think this really is some *hardware* issue.

    > --linas

    MBR, Sergei
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