Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754214AbdDEHrM (ORCPT ); Wed, 5 Apr 2017 03:47:12 -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 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-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2004 Lines: 46 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: --- 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; -- 2.12.2