From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:49497 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933279AbdDELVJ (ORCPT ); Wed, 5 Apr 2017 07:21:09 -0400 Date: Wed, 5 Apr 2017 13:21:04 +0200 From: Michal Hocko To: Vlastimil Babka Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, 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, Andrey Ryabinin Subject: Re: [PATCH 1/4] mm: prevent potential recursive reclaim due to clearing PF_MEMALLOC Message-ID: <20170405112104.GJ6035@dhcp22.suse.cz> References: <20170405074700.29871-1-vbabka@suse.cz> <20170405074700.29871-2-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170405074700.29871-2-vbabka@suse.cz> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Wed 05-04-17 09:46:57, 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 > 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 > --- > 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 -- Michal Hocko SUSE Labs