linux-kernel - Re: [PATCH] mm: softdirty: keep bit when zapping file pte

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Message-ID: <20140925063006.GN2227@moon>
Date:	Thu, 25 Sep 2014 10:30:06 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Peter Feiner <pfeiner@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Jamie Liu <jamieliu@...gle.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH] mm: softdirty: keep bit when zapping file pte

On Wed, Sep 24, 2014 at 02:59:27PM -0700, Andrew Morton wrote:
> On Sat, 20 Sep 2014 01:03:07 -0700 Peter Feiner <pfeiner@...gle.com> wrote:
> 
> > Fixes the same bug as b43790eedd31e9535b89bbfa45793919e9504c34 and
> > 9aed8614af5a05cdaa32a0b78b0f1a424754a958 where the return value of
> > pte_*mksoft_dirty was being ignored.
> > 
> > To be sure that no other pte/pmd "mk" function return values were
> > being ignored, I annotated the functions in
> > arch/x86/include/asm/pgtable.h with __must_check and rebuilt.
> > 
> 
> Grumble.
> 
> It is useful to identify preceding similar patches but that isn't a
> good way of describing *this* patch.  What is wrong with the current
> code, how does the patch fix it.

The userspace effect is that without this patch softdirty mark might be lost
if file mapped pte get zapped. It should go into @stable series after 3.12.

> 
> And, particularly, what do you think are the end-user visible effects
> of the bug?  This info helps people to work out which kernel versions
> need the fix.
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