list_lru: organize all list_lrus to list

To make list_lru memcg aware, we need all list_lrus to be kept on a list
protected by a mutex, so that we could sleep while walking over the
list.

Therefore after this change list_lru_destroy may sleep. Fortunately,
there is only one user that calls it from an atomic context - it's
put_super - and we can easily fix it by calling list_lru_destroy before
put_super in destroy_locked_super - anyway we don't longer need lrus by
that time.

Another point that should be noted is that list_lru_destroy is allowed
to be called on an uninitialized zeroed-out object, in which case it is
a no-op. Before this patch this was guaranteed by kfree, but now we
need an explicit check there.

Signed-off-by: Vladimir Davydov <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Greg Thelen <[e-mail]>
Cc: Glauber Costa <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/super.c

···
 		unregister_shrinker(&s->s_shrink);
 		fs->kill_sb(s);
 
+		/*
+		 * Since list_lru_destroy() may sleep, we cannot call it from
+		 * put_super(), where we hold the sb_lock. Therefore we destroy
+		 * the lru lists right now.
+		 */
+		list_lru_destroy(&s->s_dentry_lru);
+		list_lru_destroy(&s->s_inode_lru);
+
 		put_filesystem(fs);
 		put_super(s);
 	} else {

include/linux/list_lru.h

···
 
 struct list_lru {
 	struct list_lru_node	*node;
+#ifdef CONFIG_MEMCG_KMEM
+	struct list_head	list;
+#endif
 };
 
 void list_lru_destroy(struct list_lru *lru);

mm/list_lru.c

···
 #include <linux/mm.h>
 #include <linux/list_lru.h>
 #include <linux/slab.h>
+#include <linux/mutex.h>
+
+#ifdef CONFIG_MEMCG_KMEM
+static LIST_HEAD(list_lrus);
+static DEFINE_MUTEX(list_lrus_mutex);
+
+static void list_lru_register(struct list_lru *lru)
+{
+	mutex_lock(&list_lrus_mutex);
+	list_add(&lru->list, &list_lrus);
+	mutex_unlock(&list_lrus_mutex);
+}
+
+static void list_lru_unregister(struct list_lru *lru)
+{
+	mutex_lock(&list_lrus_mutex);
+	list_del(&lru->list);
+	mutex_unlock(&list_lrus_mutex);
+}
+#else
+static void list_lru_register(struct list_lru *lru)
+{
+}
+
+static void list_lru_unregister(struct list_lru *lru)
+{
+}
+#endif /* CONFIG_MEMCG_KMEM */
 
 bool list_lru_add(struct list_lru *lru, struct list_head *item)
 {
···
 		INIT_LIST_HEAD(&lru->node[i].list);
 		lru->node[i].nr_items = 0;
 	}
+	list_lru_register(lru);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(list_lru_init_key);
 
 void list_lru_destroy(struct list_lru *lru)
 {
+	/* Already destroyed or not yet initialized? */
+	if (!lru->node)
+		return;
+	list_lru_unregister(lru);
 	kfree(lru->node);
+	lru->node = NULL;
 }
 EXPORT_SYMBOL_GPL(list_lru_destroy);