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Date: Wed, 17 Jun 2009 09:21:27 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: sivanich@....com Cc: kosaki.motohiro@...fujitsu.com, cl@...ux-foundation.org, mel@....ul.ie, nickpiggin@...oo.com.au, linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, akpm@...ux-foundation.org Subject: Re: + page_alloc-oops-when-setting-percpu_pagelist_fraction.patch added to -mm tree (switch to lkml) Sorry for late review. > > The patch titled > page_alloc: Oops when setting percpu_pagelist_fraction > has been added to the -mm tree. Its filename is > page_alloc-oops-when-setting-percpu_pagelist_fraction.patch > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/SubmitChecklist when testing your code *** > > See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find > out what to do about this > > The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ > > ------------------------------------------------------ > Subject: page_alloc: Oops when setting percpu_pagelist_fraction > From: Dimitri Sivanich <sivanich@....com> > > After downing/upping a cpu, an attempt to set > /proc/sys/vm/percpu_pagelist_fraction results in an oops in > percpu_pagelist_fraction_sysctl_handler(). > > To reproduce this: > localhost:/sys/devices/system/cpu/cpu6 # echo 0 >online > localhost:/sys/devices/system/cpu/cpu6 # echo 1 >online > localhost:/sys/devices/system/cpu/cpu6 # cd /proc/sys/vm > localhost:/proc/sys/vm # echo 100000 >percpu_pagelist_fraction > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000004 > IP: [<ffffffff80286946>] percpu_pagelist_fraction_sysctl_handler+0x4a/0x96 > > This is because the zone->pageset[cpu] value has not been set when the cpu > has been brought back up for unpopulated zones (the "Movable" zone in the > case I'm running into). Prior to downing/upping the cpu it had been set > to &boot_pageset[cpu]. > > There are two possible fixes that come to mind. One is to check for an > unpopulated zone or NULL zone pageset for that cpu in > percpu_pagelist_fraction_sysctl_handler(), and simply not set a pagelist > highmark for that zone/cpu combination. > > The other, and the one I'm proposing here, is to set the zone's pageset > back to the boot_pageset when the cpu is brought back up if the zone is > unpopulated. > > Signed-off-by: Dimitri Sivanich <sivanich@....com> > Cc: Nick Piggin <nickpiggin@...oo.com.au> > Cc: Christoph Lameter <cl@...ux-foundation.org> > Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> > Cc: Mel Gorman <mel@....ul.ie> > Cc: <stable@...nel.org> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> > --- > > mm/page_alloc.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff -puN mm/page_alloc.c~page_alloc-oops-when-setting-percpu_pagelist_fraction mm/page_alloc.c > --- a/mm/page_alloc.c~page_alloc-oops-when-setting-percpu_pagelist_fraction > +++ a/mm/page_alloc.c > @@ -2806,7 +2806,11 @@ static int __cpuinit process_zones(int c > > node_set_state(node, N_CPU); /* this node has a cpu */ > > - for_each_populated_zone(zone) { > + for_each_zone(zone) { > + if (!populated_zone(zone)) { > + zone_pcp(zone, cpu) = &boot_pageset[cpu]; > + continue; > + } > zone_pcp(zone, cpu) = kmalloc_node(sizeof(struct per_cpu_pageset), > GFP_KERNEL, node); > if (!zone_pcp(zone, cpu)) I don't think this code works. pcp is only protected local_irq_save(), not spin lock. it assume each cpu have different own pcp. but this patch break this assumption. Now, we can share boot_pageset by multiple cpus. > _ > > Patches currently in -mm which might be from sivanich@....com are > > page_alloc-oops-when-setting-percpu_pagelist_fraction.patch > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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