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%3Ba=su...

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