linux-kernel - Re: [RFC][PATCH] EXT3: problem with page fault inside a transaction

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Message-ID: <452DE82F.3080803@yahoo.com.au>
Date:	Thu, 12 Oct 2006 17:01:03 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...l.org>
CC:	Dmitriy Monakhov <dmonakhov@...nvz.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Memory Management <linux-mm@...ck.org>,
	devel@...nvz.org, ext2-devel@...ts.sourceforge.net,
	Andrey Savochkin <saw@...oft.com>
Subject: Re: [RFC][PATCH] EXT3: problem with page fault inside a transaction

Andrew Morton wrote:
> On Thu, 12 Oct 2006 09:57:26 +0400
> Dmitriy Monakhov <dmonakhov@...nvz.org> wrote:
> 
> 
>>While reading Andrew's generic_file_buffered_write patches i've remembered
>>one more EXT3 issue.journal_start() in prepare_write() causes different ranking
>>violations if copy_from_user() triggers a page fault. It could cause 
>>GFP_FS allocation, re-entering into ext3 code possibly with a different
>>superblock and journal, ranking violation of journalling serialization 
>>and mmap_sem and page lock and all other kinds of funny consequences.
> 
> 
> With the stuff Nick and I are looking at, we won't take pagefaults inside
> prepare_write()/commit_write() any more.

Yep. Because the page is locked, it is too much to deal with even
without a filesystem in the picture.

-- 
SUSE Labs, Novell Inc.
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