Re: [PATCH] [BUGFIX] update mm->owner even if no next owner.

[Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>]

2011/6/12 Andrea Arcangeli <aarcange@redhat.com>:
> On Sat, Jun 11, 2011 at 07:51:36PM +0200, Johannes Weiner wrote:
>> This is a problem with the patch, but I think Kame's analysis and
>> approach to fix it are still correct.
>
> I agree with Kame's analysis too. This explains why removing the
> mmap_sem read mode introduced the problem, it was quite some
> unexpected subtleness not apparent to the naked eye, as memcg didn't
> explicitly relay on mmap_sem but it did implicitly during exit because
> of the __khugepaged_exit waiting if we were collapsing an hugepage...
>
> So the fix is safe because the task struct is freed with
> delayed_put_task_struct and that won't run until we rcu_read_unlock
> after mem_cgroup_from_task.
>
> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
>

Thank you all.

Regards,
-Kame

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