linux-kernel - [PATCH 4.14 132/159] powerpc/xmon: Avoid tripping SMP hardlockup watchdog

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Date:   Fri, 22 Dec 2017 09:46:57 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.14 132/159] powerpc/xmon: Avoid tripping SMP hardlockup watchdog

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Piggin <npiggin@...il.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@...il.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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) {