linux-kernel - Re: [PATCH] Fix __pfn_to_page(pfn) for CONFIG

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Date:	Sat, 8 Nov 2008 14:12:21 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH] Fix __pfn_to_page(pfn) for CONFIG_DISCONTIGMEM=y

On Saturday, 8 of November 2008, Pavel Machek wrote:
> Hi!
> 
> > This would be good to have in .28 IMO.
> 
> Actually, this makes sense even for .27-stable, AFAICT.

Yes, it does, but it has to be merged first. :-)

> > From: Rafael J. Wysocki <rjw@...k.pl>
> > Subject: Fix __pfn_to_page(pfn) for CONFIG_DISCONTIGMEM=y
> > 
> > Fix macro __pfn_to_page(pfn) so that it doesn't evaluate its
> > argument twice in the CONFIG_DISCONTIGMEM=y case, because 'pfn' may
> > be a result of a funtion call having side effects.
> 
> function call?

Oh, I mean __pfn_to_page(a_function(something)), where a_function() does more
than just computing the result.
 
> > For example, the hibernation code applies pfn_to_page(pfn) to the
> > result of a function returning the pfn corresponding to the next set
> > bit in a bitmap and the current bit position is modified on each
> > call.  This leads to "interesting" failures for CONFIG_DISCONTIGMEM=y
> > due to the current behavior of __pfn_to_page(pfn).
> > 
> > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > Cc: Pavel Machek <pavel@...e.cz>
> 
> Acked-by: Pavel Machek <pavel@...e.cz>
> 
> 
> >  include/asm-generic/memory_model.h |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > Index: linux-2.6/include/asm-generic/memory_model.h
> > ===================================================================
> > --- linux-2.6.orig/include/asm-generic/memory_model.h
> > +++ linux-2.6/include/asm-generic/memory_model.h
> > @@ -34,7 +34,7 @@
> >  
> >  #define __pfn_to_page(pfn)			\
> >  ({	unsigned long __pfn = (pfn);		\
> > -	unsigned long __nid = arch_pfn_to_nid(pfn);  \
> > +	unsigned long __nid = arch_pfn_to_nid(__pfn);  \
> >  	NODE_DATA(__nid)->node_mem_map + arch_local_page_offset(__pfn, __nid);\
> >  })

Thanks,
Rafael
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