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From:   David Hildenbrand <david@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     virtualization@lists.linux-foundation.org, linux-mm@kvack.org,
        David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        "Michael S . Tsirkin" <mst@redhat.com>
Subject: [PATCH v1 2/6] mm/page_isolation: don't dump_page(NULL) in set_migratetype_isolate()
Date:   Tue, 30 Jun 2020 16:26:35 +0200
Message-Id: <20200630142639.22770-3-david@redhat.com>
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Right now, if we have two isolations racing, we might trigger the
WARN_ON_ONCE() and to dump_page(NULL), dereferencing NULL. Let's just
return directly.

In the future, we might want to report -EAGAIN to the caller instead, as
this could indicate a temporary isolation failure only.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/page_isolation.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index f6d07c5f0d34d..553b49a34cf71 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.
-- 
2.26.2