linux-kernel - Re: kernel 3.0: BUG: soft lockup: find_get

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Date:	Mon, 31 Oct 2011 17:34:22 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Nai Xia <nai.xia@...il.com>
Cc:	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Pawel Sikora <pluto@...k.net>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	jpiszcz@...idpixels.com, arekm@...-linux.org,
	linux-kernel@...r.kernel.org
Subject: Re: kernel 3.0: BUG: soft lockup: find_get_pages+0x51/0x110

Hi Nai,

On Sat, Oct 22, 2011 at 01:07:11PM +0800, Nai Xia wrote:
> Yeah, anon_vma root lock is a big lock. And JFYI, actually I am doing 
> some very nasty hacking on anon_vma and one of the side effects is 
> breaking the root lock into pieces. But this area is pretty 
> convolved by many racing conditions. I hope some day I will finally make
> my patch work and have your precious review of it. :-)

:) It's going to be not trivial, initially it was not a shared lock
but it wasn't safe that way (especially with migrate required a
reliable rmap_walk) and using a shared lock across all
same_anon_vma/same_vma lists was the only way to be safe and solve the
races.
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