blk-throttle: Free up a group only after one rcu grace period

Soon we will allow accessing a throtl_grp under rcu_read_lock(). Hence start freeing up throtl_grp after one rcu grace period. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

blk-throttle: Free up a group only after one rcu grace period
Soon we will allow accessing a throtl_grp under rcu_read_lock(). Hence start freeing up throtl_grp after one rcu grace period. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Vivek Goyal · Jens Axboe
1 parent 5617cbef77
Showing 1 changed file with 21 additions and 1 deletions Side-by-side Diff
block/blk-throttle.c
@@ -78,6 +78,8 @@
  
 	/* Some throttle limits got updated for the group */
 	int limits_changed;
+
+	struct rcu_head rcu_head;
 };
  
 struct throtl_data
  
@@ -151,12 +153,30 @@
 	return tg;
 }
  
+static void throtl_free_tg(struct rcu_head *head)
+{
+	struct throtl_grp *tg;
+
+	tg = container_of(head, struct throtl_grp, rcu_head);
+	kfree(tg);
+}
+
 static void throtl_put_tg(struct throtl_grp *tg)
 {
 	BUG_ON(atomic_read(&tg->ref) <= 0);
 	if (!atomic_dec_and_test(&tg->ref))
 		return;
-	kfree(tg);
+
+	/*
+	 * A group is freed in rcu manner. But having an rcu lock does not
+	 * mean that one can access all the fields of blkg and assume these
+	 * are valid. For example, don't try to follow throtl_data and
+	 * request queue links.
+	 *
+	 * Having a reference to blkg under an rcu allows acess to only
+	 * values local to groups like group stats and group rate limits
+	 */
+	call_rcu(&tg->rcu_head, throtl_free_tg);
 }
  
 static void throtl_init_group(struct throtl_grp *tg)
...	...	@@ -78,6 +78,8 @@
78	78
79	79	/* Some throttle limits got updated for the group */
80	80	int limits_changed;
	81	+
	82	+ struct rcu_head rcu_head;
81	83	};
82	84
83	85	struct throtl_data
84	86
...	...	@@ -151,12 +153,30 @@
151	153	return tg;
152	154	}
153	155
	156	+static void throtl_free_tg(struct rcu_head *head)
	157	+{
	158	+ struct throtl_grp *tg;
	159	+
	160	+ tg = container_of(head, struct throtl_grp, rcu_head);
	161	+ kfree(tg);
	162	+}
	163	+
154	164	static void throtl_put_tg(struct throtl_grp *tg)
155	165	{
156	166	BUG_ON(atomic_read(&tg->ref) <= 0);
157	167	if (!atomic_dec_and_test(&tg->ref))
158	168	return;
159		- kfree(tg);
	169	+
	170	+ /*
	171	+ * A group is freed in rcu manner. But having an rcu lock does not
	172	+ * mean that one can access all the fields of blkg and assume these
	173	+ * are valid. For example, don't try to follow throtl_data and
	174	+ * request queue links.
	175	+ *
	176	+ * Having a reference to blkg under an rcu allows acess to only
	177	+ * values local to groups like group stats and group rate limits
	178	+ */
	179	+ call_rcu(&tg->rcu_head, throtl_free_tg);
160	180	}
161	181
162	182	static void throtl_init_group(struct throtl_grp *tg)