linux-kernel - Re: [PATCH] mm: page_alloc: place zone id check before VM_BUG_ON

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Message-ID: <20141209095922.GB21903@suse.de>
Date:	Tue, 9 Dec 2014 09:59:22 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Weijie Yang <weijie.yang@...sung.com>
Cc:	'Andrew Morton' <akpm@...ux-foundation.org>,
	'Johannes Weiner' <hannes@...xchg.org>,
	'Rik van Riel' <riel@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	'Weijie Yang' <weijie.yang.kh@...il.com>
Subject: Re: [PATCH] mm: page_alloc: place zone id check before
 VM_BUG_ON_PAGE check

On Tue, Dec 09, 2014 at 03:40:35PM +0800, Weijie Yang wrote:
> If the free page and its buddy has different zone id, the current
> zone->lock cann't prevent buddy page getting allocated, this could
> trigger VM_BUG_ON_PAGE in a very tiny chance:
> 

Under what circumstances can a buddy page be allocated without the
zone->lock? Any parallel allocation from that zone that takes place will
be from the per-cpu allocator and should not be affected by this. Have
you actually hit this race?

-- 
Mel Gorman
SUSE Labs
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