linux-kernel - Re: 2.6.19-rc2-mm1

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Message-ID: <4537BF8A.9040004@yahoo.com.au>
Date:	Fri, 20 Oct 2006 04:10:18 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Carsten Otte <cotte@...enet.de>
CC:	Andrew Morton <akpm@...l.org>, Cedric Le Goater <clg@...ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Gabriel C <nix.or.die@...glemail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.19-rc2-mm1

Carsten Otte wrote:
> Andrew Morton wrote:
> 
>> The page we're writing into isn't locked, so there's no deadlock afaict.
>>
>> But then, I forget how xip works.  Carsten, is it actually being used for
>> anything?
>>   
> 
> The comment may be superfluous. I did not quite understand the deadlock 
> condition refered to by the comment in filemap, therefore I cut&pasted 
> it over. I will send a patch that removes it.

Yes, it wasn't a good comment. Basically we can't hold the page lock and
then enter the page fault handler. mm-fix-pagecache-write-deadlocks.patch
has quite a lot of comments to explain it.

I don't believe filemap_xip holds the page lock, so you don't need to do
the atomic copy, and you don't need to do the fault_in_pages_readable.

-- 
SUSE Labs, Novell Inc.
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