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authorVivek Goyal <vgoyal@redhat.com>2011-05-19 15:38:27 -0400
committerJens Axboe <jaxboe@fusionio.com>2011-05-20 20:34:52 +0200
commit4843c69d496a8d2e4caab6182fe016b9a79136e0 (patch)
tree0812bb95cfc7769a3ccd90d84f303bed861c9c0a
parent5617cbef7723952cbdff28c7a10ff8a254945f4f (diff)
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>
-rw-r--r--block/blk-throttle.c22
1 files changed, 21 insertions, 1 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index b9412d1cea9..90ad40735f7 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -78,6 +78,8 @@ struct throtl_grp {
/* Some throttle limits got updated for the group */
int limits_changed;
+
+ struct rcu_head rcu_head;
};
struct throtl_data
@@ -151,12 +153,30 @@ static inline struct throtl_grp *throtl_ref_get_tg(struct throtl_grp *tg)
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)