linux-kernel - Re: [PATCH] hugetlb: fix lockdep splat caused by pmd sharing

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Date:	Tue, 30 Jul 2013 19:37:23 -0400
From:	Dave Jones <davej@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] hugetlb: fix lockdep splat caused by pmd sharing

On Wed, Jul 31, 2013 at 08:35:30AM +0900, Minchan Kim wrote:
 > > which is a false positive caused by hugetlb pmd sharing code which
 > > allocates a new pmd from withing mappint->i_mmap_mutex. If this
 > > allocation causes reclaim then the lockdep detector complains that we
 > > might self-deadlock.
 > > 
 > > This is not correct though, because hugetlb pages are not reclaimable so
 > > their mapping will be never touched from the reclaim path.
 > > 
 > > The patch tells lockup detector that hugetlb i_mmap_mutex is special
 > > by assigning it a separate lockdep class so it won't report possible
 > > deadlocks on unrelated mappings.
 > > 
 > > [peterz@...radead.org: comment for annotation]
 > > Reported-by: Dave Jones <davej@...hat.com>
 > > Signed-off-by: Michal Hocko <mhocko@...e.cz>
 > Reviewed-by: Minchan Kim <minchan@...nel.org>
 > 
 > Thanks, Michal!
 > Only remained thing is Dave's testing.

I've added it to my builds, all is quiet so far..

	Dave





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