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Date: Wed, 19 May 2010 10:21:24 -0500 (CDT)
From: Christoph Lameter <cl@...ux.com>
To: Haicheng Li <haicheng.li@...ux.intel.com>
cc: Wu Fengguang <fengguang.wu@...el.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>,
Tejun Heo <tj@...nel.org>
Subject: Re: [RESEND -v2][PATCH 3/3] mem-hotplug: fix potential race while
building zonelist for new populated zone
Looks good on its own....
On Wed, 19 May 2010, Haicheng Li wrote:
> Christoph Lameter wrote:
> > On Tue, 18 May 2010, Haicheng Li wrote:
> >
> > > +extern struct mutex zonelists_pageset_mutex;
> >
> > The mutext is used for multiple serializations having to do with zones.
> > "pageset" suggests its only for pagesets.
>
> hmm yes, "pageset" sounds a little bit confusing.
>
> > So
> >
> > zones_mutex?
> >
> > or
> >
> > zonelists_mutex?
>
> I prefer zonelists_mutex.
>
> Christoph, how about below patch? Thanks.
>
> ---
> From 3ccfd04d6ae9127bf0f5472db0b266e7b3f158bd Mon Sep 17 00:00:00 2001
> From: Haicheng Li <haicheng.li@...ux.intel.com>
> Date: Wed, 19 May 2010 11:07:21 +0800
> Subject: [PATCH] mem-hotplug: fix potential race while building zonelist for
> new populated zone
>
> Add global mutex zonelists_mutex to fix the possible race:
>
> CPU0 CPU1 CPU2
> (1) zone->present_pages += online_pages;
> (2) build_all_zonelists();
> (3)
> alloc_page();
> (4) free_page();
> (5) build_all_zonelists();
> (6) __build_all_zonelists();
> (7) zone->pageset = alloc_percpu();
>
> In step (3,4), zone->pageset still points to boot_pageset, so bad
> things may happen if 2+ nodes are in this state. Even if only 1 node
> is accessing the boot_pageset, (3) may still consume too much memory
> to fail the memory allocations in step (7).
>
> Besides, atomic operation ensures alloc_percpu() in step (7) will never fail
> since there is a new fresh memory block added in step(6).
>
> Signed-off-by: Haicheng Li <haicheng.li@...ux.intel.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> Reviewed-by: Andi Kleen <andi.kleen@...el.com>
> ---
> include/linux/mmzone.h | 1 +
> mm/memory_hotplug.c | 11 +++--------
> mm/page_alloc.c | 15 ++++++++++++++-
> 3 files changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index dbbcd50..4d87baa 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -641,6 +641,7 @@ typedef struct pglist_data {
>
> #include <linux/memory_hotplug.h>
>
> +extern struct mutex zonelists_mutex;
> void get_zone_counts(unsigned long *active, unsigned long *inactive,
> unsigned long *free);
> void build_all_zonelists(void *data);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b564b6a..bc4a942 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -389,11 +389,6 @@ int online_pages(unsigned long pfn, unsigned long
> nr_pages)
> int nid;
> int ret;
> struct memory_notify arg;
> - /*
> - * mutex to protect zone->pageset when it's still shared
> - * in onlined_pages()
> - */
> - static DEFINE_MUTEX(zone_pageset_mutex);
>
> arg.start_pfn = pfn;
> arg.nr_pages = nr_pages;
> @@ -420,14 +415,14 @@ int online_pages(unsigned long pfn, unsigned long
> nr_pages)
> * This means the page allocator ignores this zone.
> * So, zonelist must be updated after online.
> */
> - mutex_lock(&zone_pageset_mutex);
> + mutex_lock(&zonelists_mutex);
> if (!populated_zone(zone))
> need_zonelists_rebuild = 1;
>
> ret = walk_system_ram_range(pfn, nr_pages, &onlined_pages,
> online_pages_range);
> if (ret) {
> - mutex_unlock(&zone_pageset_mutex);
> + mutex_unlock(&zonelists_mutex);
> printk(KERN_DEBUG "online_pages %lx at %lx failed\n",
> nr_pages, pfn);
> memory_notify(MEM_CANCEL_ONLINE, &arg);
> @@ -441,7 +436,7 @@ int online_pages(unsigned long pfn, unsigned long
> nr_pages)
> else
> zone_pcp_update(zone);
>
> - mutex_unlock(&zone_pageset_mutex);
> + mutex_unlock(&zonelists_mutex);
> setup_per_zone_wmarks();
> calculate_zone_inactive_ratio(zone);
> if (onlined_pages) {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 72c1211..c8e6146 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2434,8 +2434,11 @@ int numa_zonelist_order_handler(ctl_table *table, int
> write,
> strncpy((char*)table->data, saved_string,
> NUMA_ZONELIST_ORDER_LEN);
> user_zonelist_order = oldval;
> - } else if (oldval != user_zonelist_order)
> + } else if (oldval != user_zonelist_order) {
> + mutex_lock(&zonelists_mutex);
> build_all_zonelists(NULL);
> + mutex_unlock(&zonelists_mutex);
> + }
> }
> out:
> mutex_unlock(&zl_order_mutex);
> @@ -2778,6 +2781,12 @@ static void setup_pageset(struct per_cpu_pageset *p,
> unsigned long batch);
> static DEFINE_PER_CPU(struct per_cpu_pageset, boot_pageset);
> static void setup_zone_pageset(struct zone *zone);
>
> +/*
> + * Global mutex to protect against size modification of zonelists
> + * as well as to serialize pageset setup for the new populated zone.
> + */
> +DEFINE_MUTEX(zonelists_mutex);
> +
> /* return values int ....just for stop_machine() */
> static __init_refok int __build_all_zonelists(void *data)
> {
> @@ -2821,6 +2830,10 @@ static __init_refok int __build_all_zonelists(void
> *data)
> return 0;
> }
>
> +/*
> + * Called with zonelists_mutex held always
> + * unless system_state == SYSTEM_BOOTING.
> + */
> void build_all_zonelists(void *data)
> {
> set_zonelist_order();
>
--
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