rcu: Move synchronize_sched_expedited() to rcutree.c

Now that TREE_RCU and TREE_PREEMPT_RCU no longer do anything different
for the single-CPU case, there is no need for multiple definitions of
synchronize_sched_expedited().  It is no longer in any sense a plug-in,
so move it from kernel/rcutree_plugin.h to kernel/rcutree.c.

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

1 files changed, 0 insertions, 116 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index cecea84..98ce17c 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -25,7 +25,6 @@
  */
 
 #include <linux/delay.h>
-#include <linux/stop_machine.h>
 
 #define RCU_KTHREAD_PRIO 1
 
@@ -1888,121 +1887,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
 
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
-static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
-static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
-
-static int synchronize_sched_expedited_cpu_stop(void *data)
-{
-	/*
-	 * There must be a full memory barrier on each affected CPU
-	 * between the time that try_stop_cpus() is called and the
-	 * time that it returns.
-	 *
-	 * In the current initial implementation of cpu_stop, the
-	 * above condition is already met when the control reaches
-	 * this point and the following smp_mb() is not strictly
-	 * necessary.  Do smp_mb() anyway for documentation and
-	 * robustness against future implementation changes.
-	 */
-	smp_mb(); /* See above comment block. */
-	return 0;
-}
-
-/*
- * Wait for an rcu-sched grace period to elapse, but use "big hammer"
- * approach to force grace period to end quickly.  This consumes
- * significant time on all CPUs, and is thus not recommended for
- * any sort of common-case code.
- *
- * Note that it is illegal to call this function while holding any
- * lock that is acquired by a CPU-hotplug notifier.  Failing to
- * observe this restriction will result in deadlock.
- *
- * This implementation can be thought of as an application of ticket
- * locking to RCU, with sync_sched_expedited_started and
- * sync_sched_expedited_done taking on the roles of the halves
- * of the ticket-lock word.  Each task atomically increments
- * sync_sched_expedited_started upon entry, snapshotting the old value,
- * then attempts to stop all the CPUs.  If this succeeds, then each
- * CPU will have executed a context switch, resulting in an RCU-sched
- * grace period.  We are then done, so we use atomic_cmpxchg() to
- * update sync_sched_expedited_done to match our snapshot -- but
- * only if someone else has not already advanced past our snapshot.
- *
- * On the other hand, if try_stop_cpus() fails, we check the value
- * of sync_sched_expedited_done.  If it has advanced past our
- * initial snapshot, then someone else must have forced a grace period
- * some time after we took our snapshot.  In this case, our work is
- * done for us, and we can simply return.  Otherwise, we try again,
- * but keep our initial snapshot for purposes of checking for someone
- * doing our work for us.
- *
- * If we fail too many times in a row, we fall back to synchronize_sched().
- */
-void synchronize_sched_expedited(void)
-{
-	int firstsnap, s, snap, trycount = 0;
-
-	/* Note that atomic_inc_return() implies full memory barrier. */
-	firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
-	get_online_cpus();
-	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
-
-	/*
-	 * Each pass through the following loop attempts to force a
-	 * context switch on each CPU.
-	 */
-	while (try_stop_cpus(cpu_online_mask,
-			     synchronize_sched_expedited_cpu_stop,
-			     NULL) == -EAGAIN) {
-		put_online_cpus();
-
-		/* No joy, try again later.  Or just synchronize_sched(). */
-		if (trycount++ < 10)
-			udelay(trycount * num_online_cpus());
-		else {
-			synchronize_sched();
-			return;
-		}
-
-		/* Check to see if someone else did our work for us. */
-		s = atomic_read(&sync_sched_expedited_done);
-		if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
-			smp_mb(); /* ensure test happens before caller kfree */
-			return;
-		}
-
-		/*
-		 * Refetching sync_sched_expedited_started allows later
-		 * callers to piggyback on our grace period.  We subtract
-		 * 1 to get the same token that the last incrementer got.
-		 * We retry after they started, so our grace period works
-		 * for them, and they started after our first try, so their
-		 * grace period works for us.
-		 */
-		get_online_cpus();
-		snap = atomic_read(&sync_sched_expedited_started);
-		smp_mb(); /* ensure read is before try_stop_cpus(). */
-	}
-
-	/*
-	 * Everyone up to our most recent fetch is covered by our grace
-	 * period.  Update the counter, but only if our work is still
-	 * relevant -- which it won't be if someone who started later
-	 * than we did beat us to the punch.
-	 */
-	do {
-		s = atomic_read(&sync_sched_expedited_done);
-		if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
-			smp_mb(); /* ensure test happens before caller kfree */
-			break;
-		}
-	} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
-
-	put_online_cpus();
-}
-EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
-
 #if !defined(CONFIG_RCU_FAST_NO_HZ)
 
 /*