Re: [PATCH] 2.5.15 IDE 62

Jens Axboe
2002-05-13T15:38:26Z

On Mon, May 13 2002, Martin Dalecki wrote:
> Uz.ytkownik Jens Axboe napisa?:
> >On Mon, May 13 2002, Martin Dalecki wrote:
> >
> >>Mon May 13 12:38:11 CEST 2002 ide-clean-62
> >>
> >>- Add missing locking around ide_do_request in do_ide_request().
> >
> >
> >This is broken, do_ide_request() is already called with the request lock
> >held. tq_disk run -> generic_unplug_device (grab lock) ->
> >__generic_unplug_device -> do_ide_request(). You just introduced a
> >deadlock.
> >
> >This code would have caused hangs or massive corruption immediately if
> >ide_lock wasn't ready held there. Not to mention instant spin_unlock
> >BUG() triggers in queue_command()
> >
>
> Oops. Indeed I see now that the ide_lock is exported to
> the upper layers above it in ide-probe.c
>
> blk_init_queue(q, do_ide_request, &ide_lock);
>
> But this is problematic in itself, since it means that
> we are basically serialiazing between *all* requests
> on all channels.

Correct.

> So I think we should have per channel locks on this level
> right? This is anyway our unit for serialization.
> (I'm just surprised that blk_init_queue() doesn't
> provide queue specific locking and relies on exported
> locks from the drivers...)

Sure go ahead and fine grain it, I had no time to go that much into
detail when ripping out io_request_lock. A drive->lock passed to
blk_init_queue would do nicely.

But beware that ide locking is a lot nastier than you think. I saw other
irq changes earlier, I just want to make sure that you are _absolutely_
certain that these changes are safe??

--
Jens Axboe