Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"

This reverts commit e59fb3120becfb36b22ddb8bd27d065d3cdca499.

This reversion was due to (extreme) boot-time slowdowns on SPARC seen by
Yinghai Lu and on x86 by Ingo
.
This is a non-trivial reversion due to intervening commits.

Conflicts:

	Documentation/RCU/trace.txt
	kernel/rcutree.c

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 3 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index ed339702481d..3f6559a5f5cd 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1520,6 +1520,7 @@ int rcu_needs_cpu(int cpu)
 {
         int c = 0;
         int snap;
+        int snap_nmi;
         int thatcpu;
 
         /* Check for being in the holdoff period. */
@@ -1530,10 +1531,10 @@ int rcu_needs_cpu(int cpu)
         for_each_online_cpu(thatcpu) {
                 if (thatcpu == cpu)
                         continue;
-                snap = atomic_add_return(0, &per_cpu(rcu_dynticks,
-                                                     thatcpu).dynticks);
+                snap = per_cpu(rcu_dynticks, thatcpu).dynticks;
+                snap_nmi = per_cpu(rcu_dynticks, thatcpu).dynticks_nmi;
                 smp_mb(); /* Order sampling of snap with end of grace period. */
-                if ((snap & 0x1) != 0) {
+                if (((snap & 0x1) != 0) || ((snap_nmi & 0x1) != 0)) {
                         per_cpu(rcu_dyntick_drain, cpu) = 0;
                         per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
                         return rcu_needs_cpu_quick_check(cpu);