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Subject[BUGFIX][PATCH] memory hotplug: fix notiier chain return value (Was Re: 2.6.28-rc4 mem_cgroup_charge_common panic)
Badari, I think you used SLUB. If so, page_cgroup's notifier callback was not
called and newly allocated page's page_cgroup wasn't allocated.
This is a fix. (notifier saw STOP_HERE flag added by slub's notifier.)

I'm now testing modified kernel, which does alloc/free page_cgroup by notifier.
(Usually, all page_cgroups are from bootmem and not freed.
so, modified a bit for test)

And I cannot reproduce panic. I think you do "real" memory hotplug other than
online/offline and saw panic caused by this.

Is this slub's behavior intentional ? page_cgroup's notifier has lower priority
than slub, now.

Thanks,
-Kame
==
notifier callback's notifier_from_errno() just works well in error
route. (It adds mask for "stop here")

Hanlder should return NOTIFY_OK in explict way.

Signed-off-by:KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/page_cgroup.c | 5 ++++-
mm/slub.c | 6 ++++--
2 files changed, 8 insertions(+), 3 deletions(-)

Index: mmotm-2.6.28-Nov10/mm/slub.c
===================================================================
--- mmotm-2.6.28-Nov10.orig/mm/slub.c
+++ mmotm-2.6.28-Nov10/mm/slub.c
@@ -3220,8 +3220,10 @@ static int slab_memory_callback(struct n
case MEM_CANCEL_OFFLINE:
break;
}
-
- ret = notifier_from_errno(ret);
+ if (ret)
+ ret = notifier_from_errno(ret);
+ else
+ ret = NOTIFY_OK;
return ret;
}

Index: mmotm-2.6.28-Nov10/mm/page_cgroup.c
===================================================================
--- mmotm-2.6.28-Nov10.orig/mm/page_cgroup.c
+++ mmotm-2.6.28-Nov10/mm/page_cgroup.c
@@ -216,7 +216,10 @@ static int page_cgroup_callback(struct n
break;
}

- ret = notifier_from_errno(ret);
+ if (ret)
+ ret = notifier_from_errno(ret);
+ else
+ ret = NOTIFY_OK;

return ret;
}



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