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From: Vlastimil Babka <vbabka@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Michal Hocko <mhocko@kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Johannes Weiner <hannes@cmpxchg.org>,
	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 <vbabka@suse.cz>,
	stable@vger.kernel.org, Andrey Ryabinin <aryabinin@virtuozzo.com>
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> (raw)
In-Reply-To: <20170405074700.29871-1-vbabka@suse.cz>

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 <aryabinin@virtuozzo.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
---
 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

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-05  7:46 [PATCH 0/4] more robust PF_MEMALLOC handling Vlastimil Babka
2017-04-05  7:46 ` Vlastimil Babka [this message]
2017-04-05 11:21   ` [PATCH 1/4] mm: prevent potential recursive reclaim due to clearing PF_MEMALLOC Michal Hocko
2017-04-05 11:40   ` Andrey Ryabinin
2017-04-07  9:21     ` Vlastimil Babka
2017-04-07  7:33   ` Hillf Danton
2017-04-05  7:46 ` [PATCH 2/4] mm: introduce memalloc_noreclaim_{save,restore} Vlastimil Babka
2017-04-05 11:28   ` Michal Hocko
2017-04-07  7:38   ` Hillf Danton
2017-04-05  7:46 ` [PATCH 3/4] treewide: convert PF_MEMALLOC manipulations to new helpers Vlastimil Babka
2017-04-05 11:30   ` Michal Hocko
2017-04-06  6:38     ` [Nbd] " Wouter Verhelst
2017-04-06 11:25       ` Mel Gorman
2017-04-05  7:47 ` [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim_*() Vlastimil Babka
2017-04-05 11:31   ` Michal Hocko
2017-04-05 11:36     ` Richard Weinberger
2017-04-05 11:39       ` Vlastimil Babka
2017-04-05 12:09         ` Michal Hocko
2017-04-06  6:33         ` Adrian Hunter
2017-04-06  7:27           ` Michal Hocko

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