[PATCH 2/2] mm/shrinker: add init_shrinker() function

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

All zeroes shrinker is now treated as 'initialized, but
not registered'. If, for some reason, you can't zero your
shrinker struct (or don't want to) then use init_shrinker()
function. Otherwise, in some cases, unregister_shrinker()
may Oops.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 include/linux/shrinker.h |  1 +
 mm/vmscan.c              | 12 ++++++++++++
 2 files changed, 13 insertions(+)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 4fcacd9..bffb660 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -67,6 +67,7 @@ struct shrinker {
 #define SHRINKER_NUMA_AWARE	(1 << 0)
 #define SHRINKER_MEMCG_AWARE	(1 << 1)
 
+extern void init_shrinker(struct shrinker *);
 extern int register_shrinker(struct shrinker *);
 extern void unregister_shrinker(struct shrinker *);
 #endif
diff --git a/mm/vmscan.c b/mm/vmscan.c
index cadc8a2..4bbcfcf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -221,6 +221,18 @@ static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
 }
 
 /*
+ * All-zeroes shrinker considered to be initialized. Use this
+ * function if you can't (don't want to) zero out your shrinker
+ * structure.
+ */
+void init_shrinker(struct shrinker *shrinker)
+{
+	shrinker->nr_deferred = NULL;
+	INIT_LIST_HEAD(&shrinker->list);
+}
+EXPORT_SYMBOL(init_shrinker);
+
+/*
  * Add a shrinker callback to be called from the vm.
  */
 int register_shrinker(struct shrinker *shrinker)
-- 
2.4.5

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