linux-kernel - Re: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic

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Date:	Sat, 25 Jul 2009 12:15:10 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"David Rientjes" <rientjes@...gle.com>, lee.schermerhorn@...com,
	kosaki.motohiro@...fujitsu.com, miaox@...fujitsu.com,
	mingo@...e.hu, a.p.zijlstra@...llo.nl, cl@...ux-foundation.org,
	menage@...gle.com, nickpiggin@...oo.com.au, y-goto@...fujitsu.com,
	penberg@...helsinki.fi, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic

KAMEZAWA Hiroyuki wrote:
> KAMEZAWA Hiroyuki wrote:
> Then, here is a much easier fix. for trusting cpuset more.
>
just a memo about memory hotplug

_Direct_ use of task->mems_allowed is only in cpuset and mempolicy.
If no policy is used, it's not checked.
(See alloc_pages_current())

memory hotplug's notifier just updates top_cpuset's mems_allowed.
But it doesn't update each task's ones.
Then, task's bahavior is

 - tasks which don't use mempolicy will use all nodes, N_HIGH_MEMORY.
 - tasks under cpuset will be controlled under their own cpuset.
 - tasks under mempolicy will use their own policy.
   but no new policy is re-calculated and, then, no new mask.

Now, even if all memory on nodes a removed, pgdat just remains.
Then, cpuset/mempolicy will never access NODE_DATA(nid) which is NULL.

Thanks,
-Kame

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