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

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Date:	Wed, 11 Oct 2006 23:43:30 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Dmitriy Monakhov <dmonakhov@...nvz.org>
Cc:	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

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.

> Our customers complain about this issue.

Really?  How often?

What on earth are they doing to trigger this?  writev() without the 2.6.18
writev() bugfix?
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