linux-kernel - Re: [PATCH] mm: Don't forget to set softdirty on file mapped fault

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Date:	Wed, 9 Jul 2014 01:15:06 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] mm: Don't forget to set softdirty on file mapped fault

On Tue, Jul 08, 2014 at 02:05:01PM -0700, Andrew Morton wrote:
> > 
> > In case if page fault happend on dirty filemapping the newly created pte
> > may loose softdirty bit thus if a userspace program is tracking memory
> > changes with help of a memory tracker (CONFIG_MEM_SOFT_DIRTY) it might
> > miss modification of a memory page (which in worts case may lead to
> > data inconsistency).
> 
> Much better, thanks.
> 
> It's a rather gross-looking bug and data inconsistency sounds serious. 
> Do you think a -stable backport is needed?

It seems the memory tracker is not that widespread in userspace
programs (I mean at the moment as far as I know only we use it
intensively) so I don't consider it as critical but moving it
into stable won't hurt. Still I fear in 3.16 the mm/memory.c
code has been significantly reworked so this patch won't apply
on its own. I can prepare a patch for 3.15 though, just say
a word.
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