Patch "powerpc/xmon: Avoid tripping SMP hardlockup watchdog" has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    powerpc/xmon: Avoid tripping SMP hardlockup watchdog

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-xmon-avoid-tripping-smp-hardlockup-watchdog.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Dec 20 18:17:52 CET 2017
From: Nicholas Piggin <npiggin@gmail.com>
Date: Fri, 29 Sep 2017 13:29:40 +1000
Subject: powerpc/xmon: Avoid tripping SMP hardlockup watchdog

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/powerpc/xmon/xmon.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -530,14 +530,19 @@ static int xmon_core(struct pt_regs *reg
 
  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 */
@@ -568,21 +573,25 @@ static int xmon_core(struct pt_regs *reg
 		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) {


Patches currently in stable-queue which might be from npiggin@gmail.com are

queue-4.14/cpuidle-fix-broadcast-control-when-broadcast-can-not-be-entered.patch
queue-4.14/powerpc-xmon-avoid-tripping-smp-hardlockup-watchdog.patch
queue-4.14/powerpc-watchdog-do-not-trigger-smp-crash-from-touch_nmi_watchdog.patch