linux-kernel - Re: 2.6.19-rc6: known regressions (v4)

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Date:	Wed, 22 Nov 2006 09:58:21 -0500
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	Pavel Emelianov <xemul@...nvz.org>,
	Linus Torvalds <torvalds@...l.org>
Cc:	Morton Andrew Morton <akpm@...l.org>, mingo@...hat.com,
	Adrian Bunk <bunk@...sta.de>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	dev@...ru
Subject: Re: 2.6.19-rc6: known regressions (v4)

On Wed, Nov 22, 2006 at 12:44:14PM +0300, Pavel Emelianov wrote:
> > I really think this is wrong.
> >
> > The original patch was wrong, and the _real_ problem is in __do_IRQ() that
> > got the desc->lock too early.
> >
> > I _think_ the correct fix is to simply revert the broken commit, and fix
> > the _one_ place that called "misnote_interrupt()" with the lock held.
> >
> > Something like this..
> >
> > I also think that the real fix will be to move the whole
> >
> > 	if (!noirqdebug)
> > 		note_interrupt(irq, desc, action_ret);
> >
> >
> > into handle_IRQ_event itself, since every caller (except for
> > "misrouted_irq()" itself, and that should probably be done separately)
> > should always do it. Right now we have a lot of people that just do
> >
> > 	action_ret = handle_IRQ_event(irq, action);
> > 	if (!noirqdebug)
> > 		note_interrupt(irq, desc, action_ret);
> >
> > explicitly.
> >
> > The only thing that keeps us from doing that is that we don't pass in
> > "desc", but we should just do that.
> >
> > But in the meantime, this appears to be the minimal fix. Can people please
> > test and verify?
> 
> This works for me, but is this normal that desc's fields are
> modified non-atomically in note_interrupt()?
> 
> And one more thing - report_bad_irq() traverses desc->action
> list without any locking either.

Works for me too. But Pavel's concern look genuine. May be we should take
the lock again in note_interrupt()/report_bad_irq() whenever we are
accessing/modifying desc.

Thanks
Vivek
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