Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756490AbaLJNio (ORCPT ); Wed, 10 Dec 2014 08:38:44 -0500 Received: from mail-ie0-f177.google.com ([209.85.223.177]:53335 "EHLO mail-ie0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755867AbaLJNin (ORCPT ); Wed, 10 Dec 2014 08:38:43 -0500 MIME-Version: 1.0 In-Reply-To: <20141209095922.GB21903@suse.de> References: <000001d01383$8e0f1120$aa2d3360$%yang@samsung.com> <20141209095922.GB21903@suse.de> Date: Wed, 10 Dec 2014 21:38:42 +0800 Message-ID: Subject: Re: [PATCH] mm: page_alloc: place zone id check before VM_BUG_ON_PAGE check From: Weijie Yang To: Mel Gorman Cc: Weijie Yang , Andrew Morton , Johannes Weiner , Rik van Riel , Linux-MM , Linux-Kernel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 9, 2014 at 5:59 PM, Mel Gorman wrote: > 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? My description maybe not clear, if the free page and its buddy is not at the same zone, the holding zone->lock cann't prevent buddy page getting allocated. zone_1->lock prevents the freeing page getting allocated zone_2->lock prevents the buddy page getting allocated they are not the same zone->lock. I found it when review the code, not a running test. However, if we cann't remove the zone_id check statement, I think we should handle this rare race. If I miss something or make a mistake, please let me know. Thanks > -- > Mel Gorman > SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/