linux-kernel - Re: [PATCH] proc: pagemap: Hold mmap

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Message-ID: <1270105771.3552.1143.camel@calx>
Date:	Thu, 01 Apr 2010 02:09:31 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	San Mehat <san@...gle.com>, linux-kernel@...r.kernel.org,
	Brian Swetland <swetland@...gle.com>,
	Dave Hansen <haveblue@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	n-horiguchi@...jp.nec.com
Subject: Re: [PATCH] proc: pagemap: Hold mmap_sem during page walk

On Thu, 2010-04-01 at 15:34 +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 1 Apr 2010 15:09:56 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> 
> >
> > +		pm.pos = 0;
> > +		start_vaddr += PAGEMAP_WALK_SIZE;
> > +		end = start_vaddr + PAGEMAP_WALK_SIZE;
> 
> Sigh...this is bad..
> 
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> In initial design, walk_page_range() was designed just for walking page table and
> it didn't require mmap_sem. Now, find_vma() etc.. are used in walk_page_range()
> and we need mmap_sem around it.

This looks pretty reasonable. However, it also looks very similar to my
first version of pagemap (which started with double-buffering). It's
going to need re-testing to make sure it hasn't reintroduced any
wrapping, alignment, or off-by-one bugs that have already been ironed
out once or twice.

-- 
http://selenic.com : development and support for Mercurial and Linux


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