From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 9DDBF6B03AB for ; Fri, 7 Apr 2017 05:21:49 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id e11so9653365wra.0 for ; Fri, 07 Apr 2017 02:21:49 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z8si33534744wmz.53.2017.04.07.02.21.47 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 07 Apr 2017 02:21:48 -0700 (PDT) Subject: Re: [PATCH 1/4] mm: prevent potential recursive reclaim due to clearing PF_MEMALLOC References: <20170405074700.29871-1-vbabka@suse.cz> <20170405074700.29871-2-vbabka@suse.cz> <1f26f654-abaf-3878-6abb-5e27ff3a289e@virtuozzo.com> From: Vlastimil Babka Message-ID: <9c6ff585-f22f-3f90-fce7-793c56485019@suse.cz> Date: Fri, 7 Apr 2017 11:21:45 +0200 MIME-Version: 1.0 In-Reply-To: <1f26f654-abaf-3878-6abb-5e27ff3a289e@virtuozzo.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrey Ryabinin , 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, stable@vger.kernel.org On 04/05/2017 01:40 PM, Andrey Ryabinin wrote: > On 04/05/2017 10:46 AM, Vlastimil Babka wrote: >> 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 > is false > >> 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; > > Perhaps this would look better: > > tsk_restore_flags(current, noreclaim_flag, PF_MEMALLOC); > > ? Well, I didn't care much considering this is for stable only, and patch 2/4 rewrites this to the new api. >> if (*compact_result <= COMPACT_INACTIVE) >> return NULL; >> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org