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.

Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Link: http://lkml.kernel.org/r/20200816125333.7434-3-david@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 63a3db1..ad3aa7a 100644 (file)
--- 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);