Re: [patch for-3.7 v2] mm, mempolicy: avoid taking mutex insidespinlock when reading numa_maps

[KOSAKI Motohiro]

>> Can't we have another way to fix ? like this ? too ugly ?
>> Again, I'm sorry if I misunderstand the points.
>>
> Sorry this patch itself may be buggy. please don't test..
> I missed that kernel/exit.c sets task->mempolicy to be NULL.
> fixed one here.
>
> --
> From 5581c71e68a7f50e52fd67cca00148911023f9f5 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Date: Thu, 18 Oct 2012 13:50:29 +0900
>
> Subject: [PATCH] hold task->mempolicy while numa_maps scans.
>
>  /proc/<pid>/numa_maps scans vma and show mempolicy under
>  mmap_sem. It sometimes accesses task->mempolicy which can
>  be freed without mmap_sem and numa_maps can show some
>  garbage while scanning.
>
> This patch tries to take reference count of task->mempolicy at reading
> numa_maps before calling get_vma_policy(). By this, task->mempolicy
> will not be freed until numa_maps reaches its end.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> V1->V2
>  -  access task->mempolicy only once and remember it.  Becase kernel/exit.c
>     can overwrite it.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

Ok, this is acceptable to me. go ahead.
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