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SubjectRe: hda: error: DMA in progress..
On Fri, Jun 21 2002, Jens Axboe wrote:
> > And now we see that it is indeed apparently really interacting with
> > the TCQ code in bad ways. But if I look down from the above code (Just
> > below in ide.c)
> >
> > if (blk_queue_plugged(&drive->queue)) {
> > BUG_ON(!drive->using_tcq);
> > break;
> > }
> >
> > It seems like the check which is catching reality right now
> > is bogous in itself. Becouse having DMA running would be
> > only problematic if the queue was still plugged. (Right?)
> > So please just disable the check.
> Not exactly, let me see if I remember the race here... The queue can
> become plugged when we queue one request with the drive (the only on the
> queue at that time), and then try to queue another right after (hence
> only a tcq issue). In that time period, we drop the queue lock, so it's
> indeed possible for the block layer to plug the queue before we reach
> the above code again. The drive can be in two states here, 1) IDE_DMA is
> set because the drive didn't release the bus (or it did, and it already
> reconnected), or 2) drive is disconnected from the bus.

Sorry that's not true (#1), it's _never_ valid for IDE_DMA to be set
here even when using TCQ (less so, if possible, for non-tcq :-). At
least according to the old semantics. That's only the case when using
speculative starts of the dma engine for tcq with release interrupt
enabled, which we don't use on Linux.

Jens Axboe

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