From: "Robert P. J. Day" <rpjday@crashcourse.ca>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Subject: Re: mm: Do not iterate over NR_CPUS in __zone_pcp_update()
Date: Tue, 9 Mar 2010 15:33:26 -0500 (EST) [thread overview]
Message-ID: <alpine.LFD.2.00.1003091530230.11928@localhost> (raw)
In-Reply-To: <20100309122253.3f3d4a53.akpm@linux-foundation.org>
On Tue, 9 Mar 2010, Andrew Morton wrote:
> On Mon, 8 Mar 2010 10:21:04 +0100 (CET)
> Thomas Gleixner <tglx@linutronix.de> wrote:
>
> > __zone_pcp_update() iterates over NR_CPUS instead of limiting the
> > access to the possible cpus. This might result in access to
> > uninitialized areas as the per cpu allocator only populates the per
> > cpu memory for possible cpus.
> >
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > ---
> > mm/page_alloc.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > Index: linux-2.6/mm/page_alloc.c
> > ===================================================================
> > --- linux-2.6.orig/mm/page_alloc.c
> > +++ linux-2.6/mm/page_alloc.c
> > @@ -3224,7 +3224,7 @@ static int __zone_pcp_update(void *data)
> > int cpu;
> > unsigned long batch = zone_batchsize(zone), flags;
> >
> > - for (cpu = 0; cpu < NR_CPUS; cpu++) {
> > + for_each_possible_cpu(cpu) {
> > struct per_cpu_pageset *pset;
> > struct per_cpu_pages *pcp;
>
> I'm having trouble working out whether we want to backport this into
> 2.6.33.x or earlier. Help?
given the above aesthetic mod, shouldn't that same change be applied
to *all* explicit loops of that form? after all, checkpatch.pl warns
against it:
=====
# use of NR_CPUS is usually wrong
# ignore definitions of NR_CPUS and usage to define arrays as likely right
if ($line =~ /\bNR_CPUS\b/ &&
$line !~ /^.\s*\s*#\s*if\b.*\bNR_CPUS\b/ &&
$line !~ /^.\s*\s*#\s*define\b.*\bNR_CPUS\b/ &&
$line !~ /^.\s*$Declare\s.*\[[^\]]*NR_CPUS[^\]]*\]/ &&
$line !~ /\[[^\]]*\.\.\.[^\]]*NR_CPUS[^\]]*\]/ &&
$line !~ /\[[^\]]*NR_CPUS[^\]]*\.\.\.[^\]]*\]/)
{
WARN("usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc\n" . $herecurr);
}
=====
rday
--
========================================================================
Robert P. J. Day Waterloo, Ontario, CANADA
Linux Consulting, Training and Kernel Pedantry.
Web page: http://crashcourse.ca
Twitter: http://twitter.com/rpjday
========================================================================
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next prev parent reply other threads:[~2010-03-09 20:35 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-08 9:21 mm: Do not iterate over NR_CPUS in __zone_pcp_update() Thomas Gleixner
2010-03-08 13:29 ` Pekka Enberg
2010-03-09 2:06 ` Tejun Heo
2010-03-09 15:10 ` Christoph Lameter
2010-03-09 20:04 ` Pekka Enberg
2010-03-09 20:19 ` Andrew Morton
2010-03-08 15:59 ` Christoph Lameter
2010-03-08 16:09 ` Mel Gorman
2010-03-09 6:34 ` KOSAKI Motohiro
2010-03-09 20:22 ` Andrew Morton
2010-03-09 20:33 ` Christoph Lameter
2010-03-09 20:33 ` Robert P. J. Day [this message]
2010-03-09 20:55 ` Christoph Lameter
2010-03-09 21:02 ` Robert P. J. Day
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