[PATCH AUTOSEL for 3.18 36/40] powerpc/xmon: Avoid tripping SMP hardlockup watchdog

[alexander.levin@verizon.com]

From: Nicholas Piggin <npiggin@gmail.com>

[ Upstream commit 064996d62a33ffe10264b5af5dca92d54f60f806 ]

The SMP hardlockup watchdog cross-checks other CPUs for lockups, which
causes xmon headaches because it's assuming interrupts hard disabled
means no watchdog troubles. Try to improve that by calling
touch_nmi_watchdog() in obvious places where secondaries are spinning.

Also annotate these spin loops with spin_begin/end calls.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
---
 arch/powerpc/xmon/xmon.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index e23f559faa47..6cec1081cb67 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -436,14 +436,19 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
 
  waiting:
 	secondary = 1;
+	spin_begin();
 	while (secondary && !xmon_gate) {
 		if (in_xmon == 0) {
-			if (fromipi)
+			if (fromipi) {
+				spin_end();
 				goto leave;
+			}
 			secondary = test_and_set_bit(0, &in_xmon);
 		}
-		barrier();
+		spin_cpu_relax();
+		touch_nmi_watchdog();
 	}
+	spin_end();
 
 	if (!secondary && !xmon_gate) {
 		/* we are the first cpu to come in */
@@ -470,21 +475,25 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
 		mb();
 		xmon_gate = 1;
 		barrier();
+		touch_nmi_watchdog();
 	}
 
  cmdloop:
 	while (in_xmon) {
 		if (secondary) {
+			spin_begin();
 			if (cpu == xmon_owner) {
 				if (!test_and_set_bit(0, &xmon_taken)) {
 					secondary = 0;
+					spin_end();
 					continue;
 				}
 				/* missed it */
 				while (cpu == xmon_owner)
-					barrier();
+					spin_cpu_relax();
 			}
-			barrier();
+			spin_cpu_relax();
+			touch_nmi_watchdog();
 		} else {
 			cmd = cmds(regs);
 			if (cmd != 0) {
-- 
2.11.0