linux-kernel - [PATCH 4/4] mm, page_alloc: Check once if a zone has isolated pageblocks -fix

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Date:	Wed, 27 Apr 2016 13:24:45 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 4/4] mm, page_alloc: Check once if a zone has isolated pageblocks -fix

Vlastimil Babka pointed out that the original code was protected by
the zone lock and provided a fix.

This is a fix to the mmotm patch
mm-page_alloc-check-once-if-a-zone-has-isolated-pageblocks.patch . Once
applied the following line should be removed from the changelog "Technically
this is race-prone but so is the existing code."

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 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 599bd1a49384..269cdb53297c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1098,9 +1098,10 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 	int migratetype = 0;
 	int batch_free = 0;
 	unsigned long nr_scanned;
-	bool isolated_pageblocks = has_isolate_pageblock(zone);
+	bool isolated_pageblocks;
 
 	spin_lock(&zone->lock);
+	isolated_pageblocks = has_isolate_pageblock(zone);
 	nr_scanned = zone_page_state(zone, NR_PAGES_SCANNED);
 	if (nr_scanned)
 		__mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned);
-- 
2.6.4