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