From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlastimil Babka 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> References: <20170405074700.29871-1-vbabka@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: nbd-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Michal Hocko , linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Johannes Weiner , Andrey Ryabinin , open-iscsi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, Mel Gorman , Vlastimil Babka To: Andrew Morton Return-path: In-Reply-To: <20170405074700.29871-1-vbabka-AlSwsSmVLrQ@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: nbd-general-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: netdev.vger.kernel.org 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 ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot