Re: [PATCH] ksm: make rmap walks more scalable

From: Linus Torvalds
Date: Thu Dec 20 2012 - 17:27:12 EST

On Thu, Dec 20, 2012 at 1:49 PM, Sasha Levin <sasha.levin@xxxxxxxxxx> wrote:
> On 12/19/2012 08:44 PM, Hugh Dickins wrote:
>> The rmap walks in ksm.c are like those in rmap.c:
>> they can safely be done with anon_vma_lock_read().
>> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
>> ---
> Hi Hugh,
> This patch didn't fix the ksm oopses I'm seeing.
> This is with both patches applied:

Looks like another NULL mm pointer in ksmd.. Hugh fixed one in
2832bc19f666 ("sched: numa: ksm: fix oops in task_numa_placment()"),
this looks like more of the same.

At a guess, it looks like get_mergeable_page() has a rmap_item with no
mm. No idea how that happened. Hugh? Some race due to something that
depended on the mmap_sem being exclusive, rather than for

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