linux-kernel - Re: [PATCH -V2] acpi: don't cond

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Message-Id: <1260510373.10543.17.camel@minggr.sh.intel.com>
Date:	Fri, 11 Dec 2009 13:46:13 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Alexey Starikovskiy <astarikovskiy@...e.de>
Cc:	Xiaotian Feng <dfeng@...hat.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	"Moore, Robert" <robert.moore@...el.com>,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH -V2] acpi: don't cond_resched if irq is disabled

On Thu, 2009-12-10 at 20:21 +0800, Alexey Starikovskiy wrote:
> Hi Xiaotian,
> 
> I think, this is another round of "armor vs. bullet" race... It will hold until
> might_sleep() logic changes again.
> 
> Please consider using preemptible() -- IMHO this is the check we should perform 
> in our case of voluntary preemption.

preemptible() may not work here because it always returns 0 for
non-preemptible kernel.

#ifdef CONFIG_PREEMPT
# define preemptible()  (preempt_count() == 0 && !irqs_disabled())
# define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
#else
# define preemptible()  0
# define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
#endif

Lin Ming

> 
> Regards,
> Alex.
> 
> 
> Xiaotian Feng пишет:
> > commit 8bd108d adds preemption point after each opcode parse, then
> > a sleeping function called from invalid context bug was founded
> > during suspend/resume stage. this was fixed in commit abe1dfa by
> > don't cond_resched when irq_disabled. But recent commit 138d156 changes
> > the behaviour to don't cond_resched when in_atomic. This makes the
> > sleeping function called from invalid context bug happen again, which
> > is reported in http://lkml.org/lkml/2009/12/1/371.
> > 
> > This patch also fixes http://bugzilla.kernel.org/show_bug.cgi?id=14483
> > 
> > Reported-and-bisected-by: Larry Finger <Larry.Finger@...inger.net>
> > Reported-and-bisected-by: Justin P. Mattock <justinmattock@...il.com>
> > Signed-off-by: Xiaotian Feng <dfeng@...hat.com>
> > Cc: Len Brown <lenb@...nel.org>
> > Cc: Bob Moore <robert.moore@...el.com>
> > Cc: Lin Ming <ming.m.lin@...el.com>
> > Cc: Alexey Starikovskiy <astarikovskiy@...e.de>
> > Cc: Pavel Machek <pavel@....cz>
> > ---
> >  include/acpi/platform/aclinux.h |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/include/acpi/platform/aclinux.h b/include/acpi/platform/aclinux.h
> > index 9d7febd..0946997 100644
> > --- a/include/acpi/platform/aclinux.h
> > +++ b/include/acpi/platform/aclinux.h
> > @@ -152,7 +152,7 @@ static inline void *acpi_os_acquire_object(acpi_cache_t * cache)
> >  #include <linux/hardirq.h>
> >  #define ACPI_PREEMPTION_POINT() \
> >  	do { \
> > -		if (!in_atomic_preempt_off()) \
> > +		if (!in_atomic_preempt_off() && !irqs_disabled()) \
> >  			cond_resched(); \
> >  	} while (0)
> >  
> 

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