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From: Peter Zijlstra <peterz@infradead.org>
To: David Brownell <david-b@pacbell.net>
Cc: Pierre Ossman <drzeus-mmc@drzeus.cx>,
	lkml <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
	Russell King <rmk@arm.linux.org.uk>,
	Nicolas Ferre <nicolas.ferre@rfo.atmel.com>,
	Andrew Victor <linux@maxim.org.za>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [patch 2.6.28-rc2] at91_mci: workaround lockdep
Date: Tue, 28 Oct 2008 18:36:56 +0100	[thread overview]
Message-ID: <1225215416.15763.32.camel@lappy.programming.kicks-ass.net> (raw)
In-Reply-To: <200810281022.42803.david-b@pacbell.net>

On Tue, 2008-10-28 at 10:22 -0700, David Brownell wrote:
> On Tuesday 28 October 2008, Peter Zijlstra wrote:
> > On Mon, 2008-10-27 at 14:26 -0700, David Brownell wrote:
> > > From: David Brownell <dbrownell@users.sourceforge.net>
> > > 
> > > Lockdep reported a problem in the at91_mci driver ... in this case, the
> > > issue is with lockdep, not with the driver. ...
> > > 
> > > When __flush_dcache_aliases() returns -- inlined into flush_dcache_page(),
> > > above -- it re-enables IRQs ... since that evidently may only be called with
> > > IRQs enabled.  That's OK since the (unshared) IRQ handler doesn't ask for IRQs
> > > to be disabled.   Except ... that lockdep went and disabled them, then went on
> > > to complains about the breakage *it* caused!
> > > 
> > > Workaround: depend on LOCKDEP=n ... 
> > 
> > In all previous such cases it was deemed the IRQ handler should deal
> > with whatever it gets.
> 
> In which case I'll wait until someone changes that IRQ handler (or that
> ARM MM utility, or lockdep), and give up using AT91 platforms for sanity
> testing kernel changes; lockdep is important, when it doesn't lie.
> 
> I do think that lockdep should warn when that it's ignoring such driver
> requests, however.  I seem to have been tripping over it a lot lately,
> and knowing that IRQ handlers were using strange modes would have saved
> a bunch of time from being wasted.
> 
> Threaded IRQ handlers are going to need to rely even more on running
> with IRQs enabled ... not to mention needing to sleep.  So it's clear
> to me that there *are* lockdep issues yet to be adressed here.

Sure, care so send a patch fixing those? :-)


  reply	other threads:[~2008-10-28 17:37 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-27 21:26 David Brownell
2008-10-28 17:04 ` Peter Zijlstra
2008-10-28 17:22   ` David Brownell
2008-10-28 17:36     ` Peter Zijlstra [this message]
2008-10-28 19:41       ` David Brownell
2008-10-29  7:20     ` David Brownell
2008-11-03 13:47     ` Nicolas Ferre
2008-11-17  9:28 ` Nicolas Ferre
2008-11-19 18:45   ` Pierre Ossman
2008-11-20 15:02     ` Nicolas Ferre
2008-11-20 15:42       ` Pierre Ossman
2008-11-23 14:26   ` Peter Zijlstra

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