linux-kernel - Re: [PATCH 1/3] Preserve the dirty bit in init_page

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Message-ID: <m1wsys6vwo.fsf@ebiederm.dsl.xmission.com>
Date:	Mon, 28 May 2007 23:28:23 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Preserve the dirty bit in init_page_buffers

Nick Piggin <nickpiggin@...oo.com.au> writes:

> Eric W. Biederman wrote:
>> Nick Piggin <nickpiggin@...oo.com.au> writes:
>
>>> However we
>>>could still set_page_dirty of a block device page without buffers
>>>via an mmap.
>>
>>
>> After the page is made dirty via mmap we have:
>> sys_write -> ... -> block_prepare_write -> ... -> create_empty_buffers.
>
> Yep, that's what I mean.
>
>
>> I suspect that is a pretty rare case but it does indeed seem to exist
>> as a problem.
>
> I think so too. But either we have some misunderstanding of the
> codepaths involved, or the author of the comments there didn't
> consider this case, so...

Which is likely.

Which is why I brought up the try_to_free_buffers case.

There has been some significant dancing around trying to
sort things out and make them race free in this code.

Eric
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