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Date: Tue, 30 Jul 2013 19:37:23 -0400
From: Dave Jones <davej@redhat.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>, Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Rik van Riel <riel@redhat.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Hillf Danton <dhillf@gmail.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH] hugetlb: fix lockdep splat caused by pmd sharing
Message-ID: <20130730233722.GA28747@redhat.com>
Mail-Followup-To: Dave Jones <davej@redhat.com>,
	Minchan Kim <minchan@kernel.org>, Michal Hocko <mhocko@suse.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	Rik van Riel <riel@redhat.com>,
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	Hillf Danton <dhillf@gmail.com>, linux-kernel@vger.kernel.org,
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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@infradead.org: comment for annotation]
 > > Reported-by: Dave Jones <davej@redhat.com>
 > > Signed-off-by: Michal Hocko <mhocko@suse.cz>
 > Reviewed-by: Minchan Kim <minchan@kernel.org>
 > 
 > Thanks, Michal!
 > Only remained thing is Dave's testing.

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

	Dave