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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-01-31 14:00:41 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-02-21 09:06:08 -0800
commit236fefafe5d3d34b78ed2ccf5510909716112326 (patch)
tree9ff5ec129e59667341aa07120720b6e4a5ced4d9 /include/linux
parent2036d94a7b61ca5032ce90f2bda06afec0fe713e (diff)
rcu: Call out dangers of expedited RCU primitives
The expedited RCU primitives can be quite useful, but they have some high costs as well. This commit updates and creates docbook comments calling out the costs, and updates the RCU documentation as well. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/rcutree.h16
1 files changed, 16 insertions, 0 deletions
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 73892483fd0..e8ee5dd0854 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -63,6 +63,22 @@ extern void synchronize_rcu_expedited(void);
void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
+/**
+ * synchronize_rcu_bh_expedited - Brute-force RCU-bh grace period
+ *
+ * Wait for an RCU-bh grace period to elapse, but use a "big hammer"
+ * approach to force the grace period to end quickly. This consumes
+ * significant time on all CPUs and is unfriendly to real-time workloads,
+ * so is thus not recommended for any sort of common-case code. In fact,
+ * if you are using synchronize_rcu_bh_expedited() in a loop, please
+ * restructure your code to batch your updates, and then use a single
+ * synchronize_rcu_bh() instead.
+ *
+ * Note that it is illegal to call this function while holding any lock
+ * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
+ * to call this function from a CPU-hotplug notifier. Failing to observe
+ * these restriction will result in deadlock.
+ */
static inline void synchronize_rcu_bh_expedited(void)
{
synchronize_sched_expedited();