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

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Message-ID: <20140708204017.GG17860@moon.sw.swsoft.com>
Date:	Wed, 9 Jul 2014 00:40:17 +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 01:19:20PM -0700, Andrew Morton wrote:
> On Tue, 8 Jul 2014 23:21:51 +0400 Cyrill Gorcunov <gorcunov@...il.com> wrote:
> 
> > Otherwise we may not notice that pte was softdirty because pte_mksoft_dirty
> > helper _returns_ new pte but not modifies argument.
> 
> When fixing a bug, please describe the end-user visible effects of that
> bug.
> 
> [for the 12,000th time :(]

"we may not notice that pte was softdirty" I thought it's enough, because
that's the effect user sees -- pte is not dirtified where it should.

Really sorry Andrew if I were not clear enough. What about: In case if page
fault happend on dirty filemapping the newly created pte may not
notice if old one were already softdirtified because pte_mksoft_dirty
doesn't modify its argument but rather returns new pte value.
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