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

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Message-ID: <465A6197.5010402@yahoo.com.au>
Date:	Mon, 28 May 2007 14:59:03 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
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 wrote:
> Eric W. Biederman wrote:

>> When we initialize the ramdisk by writing to /dev/ram0 usually in
>> init/do_mounts_rd.c we don't allocate buffer heads but we do set
>> the dirty bit, and the page is in the page cache.  So when we
>> later call getblk it reuses the same page and then calls
>> init_page_buffers.
> 
> 
> Hmm, so this would be a problem for block_dev.c as well, then?
> Because it would be possible to have a dirty block dev page
> have its buffers reclaimed and then reinitialised via
> init_page_buffers, AFAIKS.

Oh, no, try_to_free_buffers won't drop dirty buffers. However we
could still set_page_dirty of a block device page without buffers
via an mmap.

-- 
SUSE Labs, Novell Inc.
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