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authorTejun Heo <tj@kernel.org>2013-05-14 13:52:31 -0700
committerTejun Heo <tj@kernel.org>2013-05-14 13:52:31 -0700
commit2a4fd070ee8561d918a3776388331bb7e92ea59e (patch)
tree53eb9c6df1ea0e02cb3f3442fb85f9e25a4691ed /block
parentdb61367038dcd222476881cb09fd54661b3cd508 (diff)
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blkcg: move bulk of blkcg_gq release operations to the RCU callback
Currently, when the last reference of a blkcg_gq is put, all then release operations sans the actual freeing happen directly in blkg_put(). As blkg_put() may be called under queue_lock, all pd_exit_fn()s may be too. This makes it impossible for pd_exit_fn()s to use del_timer_sync() on timers which grab the queue_lock which is an irq-safe lock due to the deadlock possibility described in the comment on top of del_timer_sync(). This can be easily avoided by perfoming the release operations in the RCU callback instead of directly from blkg_put(). This patch moves the blkcg_gq release operations to the RCU callback. As this leaves __blkg_release() with only call_rcu() invocation, blkg_rcu_free() is renamed to __blkg_release_rcu(), exported and call_rcu() invocation is now done directly from blkg_put() instead of going through __blkg_release() which is removed. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Vivek Goyal <vgoyal@redhat.com>
Diffstat (limited to 'block')
-rw-r--r--block/blk-cgroup.c34
-rw-r--r--block/blk-cgroup.h4
2 files changed, 18 insertions, 20 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 6bbe0a939596..d0747605f56c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -369,13 +369,17 @@ static void blkg_destroy_all(struct request_queue *q)
q->root_rl.blkg = NULL;
}
-static void blkg_rcu_free(struct rcu_head *rcu_head)
-{
- blkg_free(container_of(rcu_head, struct blkcg_gq, rcu_head));
-}
-
-void __blkg_release(struct blkcg_gq *blkg)
+/*
+ * A group is RCU protected, 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 accesses to only values
+ * local to groups like group stats and group rate limits.
+ */
+void __blkg_release_rcu(struct rcu_head *rcu_head)
{
+ struct blkcg_gq *blkg = container_of(rcu_head, struct blkcg_gq, rcu_head);
int i;
/* tell policies that this one is being freed */
@@ -388,21 +392,15 @@ void __blkg_release(struct blkcg_gq *blkg)
/* release the blkcg and parent blkg refs this blkg has been holding */
css_put(&blkg->blkcg->css);
- if (blkg->parent)
+ if (blkg->parent) {
+ spin_lock_irq(blkg->q->queue_lock);
blkg_put(blkg->parent);
+ spin_unlock_irq(blkg->q->queue_lock);
+ }
- /*
- * 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(&blkg->rcu_head, blkg_rcu_free);
+ blkg_free(blkg);
}
-EXPORT_SYMBOL_GPL(__blkg_release);
+EXPORT_SYMBOL_GPL(__blkg_release_rcu);
/*
* The next function used by blk_queue_for_each_rl(). It's a bit tricky
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index e15f731d2cdd..8056c03a3382 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -266,7 +266,7 @@ static inline void blkg_get(struct blkcg_gq *blkg)
blkg->refcnt++;
}
-void __blkg_release(struct blkcg_gq *blkg);
+void __blkg_release_rcu(struct rcu_head *rcu);
/**
* blkg_put - put a blkg reference
@@ -279,7 +279,7 @@ static inline void blkg_put(struct blkcg_gq *blkg)
lockdep_assert_held(blkg->q->queue_lock);
WARN_ON_ONCE(blkg->refcnt <= 0);
if (!--blkg->refcnt)
- __blkg_release(blkg);
+ call_rcu(&blkg->rcu_head, __blkg_release_rcu);
}
struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg, struct request_queue *q,