linux-kernel - [PATCH v5 2/6] mm/page_isolation: exit early when pageblock is isolated in set_migratetype

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Date:   Sun, 16 Aug 2020 14:53:29 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        David Hildenbrand <david@...hat.com>,
        Baoquan He <bhe@...hat.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Michael S . Tsirkin" <mst@...hat.com>, Qian Cai <cai@....pw>
Subject: [PATCH v5 2/6] mm/page_isolation: exit early when pageblock is isolated in set_migratetype_isolate()

Right now, if we have two isolations racing on a pageblock that's in the
MOVABLE zone, we would trigger the WARN_ON_ONCE(). Let's just return
directly, simplifying error handling.

The change was introduced in commit 3d680bdf60a5 ("mm/page_isolation: fix
potential warning from user"). As far as I can see, we currently don't have
alloc_contig_range() users that use the ZONE_MOVABLE (anymore), so it's
currently more a cleanup and a preparation for the future than a fix.

Reviewed-by: Baoquan He <bhe@...hat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@...il.com>
Acked-by: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: Qian Cai <cai@....pw>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/page_isolation.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index f6d07c5f0d34d..7d7d263ce7f4b 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -29,10 +29,12 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
 	/*
 	 * We assume the caller intended to SET migrate type to isolate.
 	 * If it is already set, then someone else must have raced and
-	 * set it before us.  Return -EBUSY
+	 * set it before us.
 	 */
-	if (is_migrate_isolate_page(page))
-		goto out;
+	if (is_migrate_isolate_page(page)) {
+		spin_unlock_irqrestore(&zone->lock, flags);
+		return -EBUSY;
+	}
 
 	/*
 	 * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
@@ -52,7 +54,6 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
 		ret = 0;
 	}
 
-out:
 	spin_unlock_irqrestore(&zone->lock, flags);
 	if (!ret) {
 		drain_all_pages(zone);
-- 
2.26.2