From patchwork Wed Apr 5 07:46:57 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vlastimil Babka X-Patchwork-Id: 9663165 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id D69A760352 for ; Wed, 5 Apr 2017 07:47:12 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C81AA262FF for ; Wed, 5 Apr 2017 07:47:12 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id BC890269DA; Wed, 5 Apr 2017 07:47:12 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3DB0B262FF for ; Wed, 5 Apr 2017 07:47:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753780AbdDEHrL (ORCPT ); Wed, 5 Apr 2017 03:47:11 -0400 Received: from mx2.suse.de ([195.135.220.15]:51288 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753661AbdDEHrJ (ORCPT ); Wed, 5 Apr 2017 03:47:09 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 8A72BAAB2; Wed, 5 Apr 2017 07:47:07 +0000 (UTC) From: Vlastimil Babka To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Mel Gorman , Johannes Weiner , linux-block@vger.kernel.org, nbd-general@lists.sourceforge.net, open-iscsi@googlegroups.com, linux-scsi@vger.kernel.org, netdev@vger.kernel.org, Vlastimil Babka , stable@vger.kernel.org, Andrey Ryabinin Subject: [PATCH 1/4] mm: prevent potential recursive reclaim due to clearing PF_MEMALLOC Date: Wed, 5 Apr 2017 09:46:57 +0200 Message-Id: <20170405074700.29871-2-vbabka@suse.cz> X-Mailer: git-send-email 2.12.2 In-Reply-To: <20170405074700.29871-1-vbabka@suse.cz> References: <20170405074700.29871-1-vbabka@suse.cz> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The function __alloc_pages_direct_compact() sets PF_MEMALLOC to prevent deadlock during page migration by lock_page() (see the comment in __unmap_and_move()). Then it unconditionally clears the flag, which can clear a pre-existing PF_MEMALLOC flag and result in recursive reclaim. This was not a problem until commit a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath"), because direct compation was called only after direct reclaim, which was skipped when PF_MEMALLOC flag was set. Even now it's only a theoretical issue, as the new callsite of __alloc_pages_direct_compact() is reached only for costly orders and when gfp_pfmemalloc_allowed() is true, which means either __GFP_NOMEMALLOC is in gfp_flags or in_interrupt() is true. There is no such known context, but let's play it safe and make __alloc_pages_direct_compact() robust for cases where PF_MEMALLOC is already set. Fixes: a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath") Reported-by: Andrey Ryabinin Signed-off-by: Vlastimil Babka Cc: Acked-by: Michal Hocko Acked-by: Hillf Danton --- mm/page_alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3589f8be53be..b84e6ffbe756 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3288,6 +3288,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, enum compact_priority prio, enum compact_result *compact_result) { struct page *page; + unsigned int noreclaim_flag = current->flags & PF_MEMALLOC; if (!order) return NULL; @@ -3295,7 +3296,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, current->flags |= PF_MEMALLOC; *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, prio); - current->flags &= ~PF_MEMALLOC; + current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag; if (*compact_result <= COMPACT_INACTIVE) return NULL;