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Re: ext4dev build failure on mips: "empty_zero_page" undefined

To: Dmitri Vorobiev <dmitri.vorobiev@gmail.com>
Subject: Re: ext4dev build failure on mips: "empty_zero_page" undefined
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 13 May 2008 06:12:52 +0100
Cc: Theodore Tso <tytso@mit.edu>, Martin Michlmayr <tbm@cyrius.com>, linux-mips@linux-mips.org, linux-ext4@vger.kernel.org
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On Tue, May 13, 2008 at 05:50:29AM +0100, Ralf Baechle wrote:

> > Normally I push my patches via the mips tree, and now I'm Cc:ing Ralf for 
> > that.
> > 
> > Hopefully Ralf will react quickly. :)
> 
> I prefer to do it myself so I can apply it at the same time to the MIPS
> -stable branches.
> 
> I'm a little irriated that this thread seems to be only about
> empty_zero_page but apparently not zero_page_mask?  empty_zero_page is
> actualy an array of pages on MIPS and ZERO_PAGE() will pick the right one
> for a particular user space mapping based on the virtual address but
> ZERO_PAGE() also references zero_page_mask.  So I sense more brokenness
> here.

The ZERO_PAGE(0) call in ext4_ext_zeroout is the culprit.  Using a zero
argument allows the compiler to eleminate the reference to zero_page_mask.

Am I reading this right that ZERO_PAGE() is being used without any
mappings to userspace being involved?

  Ralf

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