From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BA21CA1005 for ; Tue, 5 Sep 2023 16:51:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243925AbjIEQtg (ORCPT ); Tue, 5 Sep 2023 12:49:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38200 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354543AbjIEM3I (ORCPT ); Tue, 5 Sep 2023 08:29:08 -0400 Received: from outbound-smtp08.blacknight.com (outbound-smtp08.blacknight.com [46.22.139.13]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4D2DE1A8 for ; Tue, 5 Sep 2023 05:29:01 -0700 (PDT) Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp08.blacknight.com (Postfix) with ESMTPS id B86FE1C3975 for ; Tue, 5 Sep 2023 13:28:59 +0100 (IST) Received: (qmail 3911 invoked from network); 5 Sep 2023 12:28:59 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.20.191]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 5 Sep 2023 12:28:59 -0000 Date: Tue, 5 Sep 2023 13:28:57 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Lecopzer Chen , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, nsaenzju@redhat.com, yj.chiang@mediatek.com, Mark-pk Tsai , Joe Liu Subject: Re: [PATCH] mm: page_alloc: fix cma pageblock was stolen in rmqueue fallback Message-ID: <20230905122857.b3kwlxm6qxa2tgpb@techsingularity.net> References: <20230830111332.7599-1-lecopzer.chen@mediatek.com> <20230905090922.zy7srh33rg5c3zao@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 05, 2023 at 11:37:30AM +0200, Vlastimil Babka wrote: > On 9/5/23 11:09, Mel Gorman wrote: > > On Wed, Aug 30, 2023 at 07:13:33PM +0800, Lecopzer Chen wrote: > >> commit 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a > >> spinlock") fallback freeing page to free_one_page() if pcp trylock > >> failed. This make MIGRATE_CMA be able to fallback and be stolen > >> whole pageblock by MIGRATE_UNMOVABLE in the page allocation. > >> > >> PCP free is fine because free_pcppages_bulk() will always get > >> migratetype again before freeing the page, thus this only happen when > >> someone tried to put CMA page in to other MIGRATE_TYPE's freelist. > >> > >> Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock") > >> Reported-by: Joe Liu > >> Signed-off-by: Lecopzer Chen > >> Cc: Mark-pk Tsai > >> Cc: Joe Liu > > > > Sorry for the long delay and thanks Lecopzer for the patch. > > > > This changelog is difficult to parse but the fix may also me too specific > > and could be more robust against types other than CMA. It is true that > > a failed PCP acquire may return a !is_migrate_isolate page to the wrong > > list but it's more straight-forward to unconditionally lookup the PCP > > migratetype of the spinlock is not acquired. > > > > How about this? It unconditionally looks up the PCP migratetype after > > spinlock contention. It's build tested only > > > > --8<-- > > mm: page_alloc: Free pages to correct buddy list after PCP lock contention > > > > Commit 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock") > > returns pages to the buddy list on PCP lock contention. However, for > > migratetypes that are not MIGRATE_PCPTYPES, the migratetype may have > > been clobbered already for pages that are not being isolated. In > > practice, this means that CMA pages may be returned to the wrong > > buddy list. While this might be harmless in some cases as it is > > MIGRATE_MOVABLE, the pageblock could be reassigned in rmqueue_fallback > > and prevent a future CMA allocation. Lookup the PCP migratetype > > against unconditionally if the PCP lock is contended. > > > > [lecopzer.chen@mediatek.com: CMA-specific fix] > > Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock") > > I think we should Cc: stable for the sake of 6.1 LTS? > Yep. > > Reported-by: Joe Liu > > Signed-off-by: Mel Gorman > > Acked-by: Vlastimil Babka > Thanks. -- Mel Gorman SUSE Labs