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

powerpc/watchdog: Do not trigger SMP crash from touch_nmi_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-watchdog-do-not-trigger-smp-crash-from-touch_nmi_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 13:29:39 +1000 Subject: powerpc/watchdog: Do not trigger SMP crash from touch_nmi_watchdog

From: Nicholas Piggin npiggin@gmail.com

[ Upstream commit 80e4d70b06863e0104e5a0dc78aa3710297fbd4b ]

In xmon, touch_nmi_watchdog() is not expected to be checking that other CPUs have not touched the watchdog, so the code will just call touch_nmi_watchdog() once before re-enabling hard interrupts.

Just update our CPU's state, and ignore apparently stuck SMP threads.

Arguably touch_nmi_watchdog should check for SMP lockups, and callers should be fixed, but that's not trivial for the input code of xmon.

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/kernel/watchdog.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/powerpc/kernel/watchdog.c +++ b/arch/powerpc/kernel/watchdog.c @@ -276,9 +276,12 @@ void arch_touch_nmi_watchdog(void) { unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000; int cpu = smp_processor_id(); + u64 tb = get_tb();

- if (get_tb() - per_cpu(wd_timer_tb, cpu) >= ticks) - watchdog_timer_interrupt(cpu); + if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) { + per_cpu(wd_timer_tb, cpu) = tb; + wd_smp_clear_cpu_pending(cpu, tb); + } } EXPORT_SYMBOL(arch_touch_nmi_watchdog);

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