X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=kernel%2Frcupdate.c;h=d92a76a881aa47a9aa059c3221910834f6c50cf8;hb=09664fda48c5dd63277f1f42888ca9d5dca6037a;hp=467d5940f62406c35ab64fb7c4c88b1556154fa0;hpb=01dcb0443ed89eccf26c2b43f1ea13b368ae740d;p=safe%2Fjmp%2Flinux-2.6

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 467d594..d92a76a 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -77,8 +77,15 @@ void wakeme_after_rcu(struct rcu_head  *head)
  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  * and may be nested.
  */
-void synchronize_rcu(void);	/* Makes kernel-doc tools happy */
-synchronize_rcu_xxx(synchronize_rcu, call_rcu)
+void synchronize_rcu(void)
+{
+	struct rcu_synchronize rcu;
+	init_completion(&rcu.completion);
+	/* Will wake me after RCU finished. */
+	call_rcu(&rcu.head, wakeme_after_rcu);
+	/* Wait for it. */
+	wait_for_completion(&rcu.completion);
+}
 EXPORT_SYMBOL_GPL(synchronize_rcu);
 
 static void rcu_barrier_callback(struct rcu_head *notused)
@@ -119,18 +126,19 @@ static void _rcu_barrier(enum rcu_barrier type)
 	/* Take cpucontrol mutex to protect against CPU hotplug */
 	mutex_lock(&rcu_barrier_mutex);
 	init_completion(&rcu_barrier_completion);
-	atomic_set(&rcu_barrier_cpu_count, 0);
 	/*
-	 * The queueing of callbacks in all CPUs must be atomic with
-	 * respect to RCU, otherwise one CPU may queue a callback,
-	 * wait for a grace period, decrement barrier count and call
-	 * complete(), while other CPUs have not yet queued anything.
-	 * So, we need to make sure that grace periods cannot complete
-	 * until all the callbacks are queued.
+	 * Initialize rcu_barrier_cpu_count to 1, then invoke
+	 * rcu_barrier_func() on each CPU, so that each CPU also has
+	 * incremented rcu_barrier_cpu_count.  Only then is it safe to
+	 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
+	 * might complete its grace period before all of the other CPUs
+	 * did their increment, causing this function to return too
+	 * early.
 	 */
-	rcu_read_lock();
+	atomic_set(&rcu_barrier_cpu_count, 1);
 	on_each_cpu(rcu_barrier_func, (void *)type, 1);
-	rcu_read_unlock();
+	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
+		complete(&rcu_barrier_completion);
 	wait_for_completion(&rcu_barrier_completion);
 	mutex_unlock(&rcu_barrier_mutex);
 }