linux-kernel - Re: [PATCH 1/2] Allow rwlocks to re-enable interrupts

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Message-Id: <1224703183.20069.55.camel@twins>
Date:	Wed, 22 Oct 2008 21:19:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Petr Tesarik <ptesarik@...e.cz>, linux-kernel@...r.kernel.org,
	linux-ia64@...r.kernel.org, tee@....com,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 1/2] Allow rwlocks to re-enable interrupts

On Wed, 2008-10-22 at 13:05 -0600, Matthew Wilcox wrote:
> On Wed, Oct 22, 2008 at 07:24:31PM +0200, Peter Zijlstra wrote:
> > > No problem. I could then also use it for _spin_lock_irqsave, if the
> > > answer to the above question is use CONFIG_LOCK_STAT there as well.
> > 
> > If you create LOCK_CONTEDED_FLAGS() the whole issue goes away nicely.

Gah, I looked at it again, and that #ifdef isn't only to select between
LOCK_CONTENDED and not, but we can't actually have the re-enable for
anything lockdep.

So I was wrong.

> Should it also be used for _spin_lock_irq()?  I'm puzzled why it's only
> used for _irqsave().

Right, not sure how this maze is done.

The thing is, with spin_lock_irq() you know the irq state and can do the
enable unconditionally - then again, with ticket locks we cannot do it
at all.

The _flags() version needs the flags to see if irqs was enabled before
we entered the op, if it wasn't we cannot go around enabling them.

> (should _spin_lock_bh() re-enable BHs while waiting?  Is it just not big
> enough of a deal?)

Doubt it.. dunno.. personally I'd rather see softirqs die sooner rather
than later.
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