rcu: Move rcu_barrier_completion to rcu_state structure

In order to allow each RCU flavor to concurrently execute its
rcu_barrier() function, it is necessary to move the relevant
state to the rcu_state structure.  This commit therefore moves the
rcu_barrier_completion global variable to a new ->barrier_completion
field in the rcu_state structure.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

kernel/rcutree.c

@@ -158,7 +158,6 @@ unsigned long rcutorture_vernum;
 /* State information for rcu_barrier() and friends. */
 
 static DEFINE_MUTEX(rcu_barrier_mutex);
-static struct completion rcu_barrier_completion;
 
 /*
  * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
@@ -2275,7 +2274,7 @@ static void rcu_barrier_callback(struct rcu_head *rhp)
 	struct rcu_state *rsp = rdp->rsp;
 
 	if (atomic_dec_and_test(&rsp->barrier_cpu_count))
-		complete(&rcu_barrier_completion);
+		complete(&rsp->barrier_completion);
 }
 
 /*
@@ -2325,7 +2324,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
 	 * 6.	Both rcu_barrier_callback() callbacks are invoked, awakening
 	 *	us -- but before CPU 1's orphaned callbacks are invoked!!!
 	 */
-	init_completion(&rcu_barrier_completion);
+	init_completion(&rsp->barrier_completion);
 	atomic_set(&rsp->barrier_cpu_count, 1);
 	raw_spin_lock_irqsave(&rsp->onofflock, flags);
 	rsp->rcu_barrier_in_progress = current;
@@ -2375,10 +2374,10 @@ static void _rcu_barrier(struct rcu_state *rsp)
 	 * CPU, and thus each counted, remove the initial count.
 	 */
 	if (atomic_dec_and_test(&rsp->barrier_cpu_count))
-		complete(&rcu_barrier_completion);
+		complete(&rsp->barrier_completion);
 
 	/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
-	wait_for_completion(&rcu_barrier_completion);
+	wait_for_completion(&rsp->barrier_completion);
 
 	/* Other rcu_barrier() invocations can now safely proceed. */
 	mutex_unlock(&rcu_barrier_mutex);

kernel/rcutree.h

@@ -401,6 +401,7 @@ struct rcu_state {
 						/* Task doing rcu_barrier(), */
 						/*  or NULL if no barrier. */
 	atomic_t barrier_cpu_count;		/* # CPUs waiting on. */
+	struct completion barrier_completion;	/* Wake at barrier end. */
 	raw_spinlock_t fqslock;			/* Only one task forcing */
 						/*  quiescent states. */
 	unsigned long jiffies_force_qs;		/* Time at which to invoke */