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SubjectRe: [PATCH AUTOSEL for 3.18 36/40] powerpc/xmon: Avoid tripping SMP hardlockup watchdog
Date
On Thu, Dec 14, 2017 at 12:10:39AM +1100, Michael Ellerman wrote:
>alexander.levin@verizon.com writes:
>
>> 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.
>
>These macros didn't exist until 4.13, and haven't been backported AFAIK.

But the touch_nmi_watchdog() bits are something we want in stable, right?

>> 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

--

Thanks,
Sasha
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