1 files changed, 44 insertions, 18 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 8914886..6789055 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2249,8 +2249,8 @@ void synchronize_rcu_bh(void)
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
 
-static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
-static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
+static atomic_long_t sync_sched_expedited_started = ATOMIC_LONG_INIT(0);
+static atomic_long_t sync_sched_expedited_done = ATOMIC_LONG_INIT(0);
 
 static int synchronize_sched_expedited_cpu_stop(void *data)
 {
@@ -2308,10 +2308,30 @@ static int synchronize_sched_expedited_cpu_stop(void *data)
  */
 void synchronize_sched_expedited(void)
 {
-	int firstsnap, s, snap, trycount = 0;
+	long firstsnap, s, snap;
+	int trycount = 0;
 
-	/* Note that atomic_inc_return() implies full memory barrier. */
-	firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
+	/*
+	 * If we are in danger of counter wrap, just do synchronize_sched().
+	 * By allowing sync_sched_expedited_started to advance no more than
+	 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
+	 * that more than 3.5 billion CPUs would be required to force a
+	 * counter wrap on a 32-bit system.  Quite a few more CPUs would of
+	 * course be required on a 64-bit system.
+	 */
+	if (ULONG_CMP_GE((ulong)atomic_read(&sync_sched_expedited_started),
+			 (ulong)atomic_read(&sync_sched_expedited_done) +
+			 ULONG_MAX / 8)) {
+		synchronize_sched();
+		return;
+	}
+
+	/*
+	 * Take a ticket.  Note that atomic_inc_return() implies a
+	 * full memory barrier.
+	 */
+	snap = atomic_long_inc_return(&sync_sched_expedited_started);
+	firstsnap = snap;
 	get_online_cpus();
 	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
 
@@ -2324,6 +2344,13 @@ void synchronize_sched_expedited(void)
 			     NULL) == -EAGAIN) {
 		put_online_cpus();
 
+		/* Check to see if someone else did our work for us. */
+		s = atomic_long_read(&sync_sched_expedited_done);
+		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
+			smp_mb(); /* ensure test happens before caller kfree */
+			return;
+		}
+
 		/* No joy, try again later.  Or just synchronize_sched(). */
 		if (trycount++ < 10) {
 			udelay(trycount * num_online_cpus());
@@ -2332,23 +2359,22 @@ void synchronize_sched_expedited(void)
 			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)) {
+		/* Recheck to see if someone else did our work for us. */
+		s = atomic_long_read(&sync_sched_expedited_done);
+		if (ULONG_CMP_GE((ulong)s, (ulong)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.
+		 * callers to piggyback on our grace period.  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);
+		snap = atomic_long_read(&sync_sched_expedited_started);
 		smp_mb(); /* ensure read is before try_stop_cpus(). */
 	}
 
@@ -2356,15 +2382,15 @@ void synchronize_sched_expedited(void)
 	 * 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.
+	 * than we did already did their update.
 	 */
 	do {
-		s = atomic_read(&sync_sched_expedited_done);
-		if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
+		s = atomic_long_read(&sync_sched_expedited_done);
+		if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
 			smp_mb(); /* ensure test happens before caller kfree */
 			break;
 		}
-	} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
+	} while (atomic_long_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
 
 	put_online_cpus();
 }