linux-kernel - Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend)

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Message-ID: <20120727084254.GA612@suse.de>
Date:	Fri, 27 Jul 2012 09:42:54 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Rik van Riel <riel@...hat.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Michal Hocko <mhocko@...e.cz>,
	Linux-MM <linux-mm@...ck.org>,
	David Gibson <david@...son.dropbear.id.au>,
	Ken Chen <kenchen@...gle.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Larry Woodman <lwoodman@...hat.com>
Subject: Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown
 of hugetlbfs shared page tables V2 (resend)

On Thu, Jul 26, 2012 at 01:42:26PM -0400, Rik van Riel wrote:
> On 07/23/2012 12:04 AM, Hugh Dickins wrote:
> 
> >Please don't be upset if I say that I don't like either of your patches.
> >Mainly for obvious reasons - I don't like Mel's because anything with
> >trylock retries and nested spinlocks worries me before I can even start
> >to think about it; and I don't like Michal's for the same reason as Mel,
> >that it spreads more change around in common paths than we would like.
> 
> I have a naive question.
> 
> In huge_pmd_share, we protect ourselves by taking
> the mapping->i_mmap_mutex.
> 
> Is there any reason we could not take the i_mmap_mutex
> in the huge_pmd_unshare path?
> 

We do, in 3.4 at least - callers of __unmap_hugepage_range hold the
i_mmap_mutex. Locking changes in mmotm and there is a patch there that
needs to be reverted. What tree are you looking at?

-- 
Mel Gorman
SUSE Labs
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