[Bionic][PATCH 1/1] powerpc/watchdog: remove arch_trigger_cpumask_backtrace

Joseph Salisbury joseph.salisbury at canonical.com
Wed Apr 11 16:09:39 UTC 2018

From: Nicholas Piggin <npiggin at gmail.com>

BugLink: http://bugs.launchpad.net/bugs/1762913

The powerpc NMI IPIs may not be recoverable if they are taken in
some sections of code, and also there have been and still are issues
with taking NMIs (in KVM guest code, in firmware, etc) which makes them
a bit dangerous to use.

Generic code like softlockup detector and rcu stall detectors really
hammer on trigger_*_backtrace, which has lead to further problems
because we've implemented it with the NMI.

So stop providing NMI backtraces for now. Importantly, the powerpc code
uses NMI IPIs in crash/debug, and the SMP hardlockup watchdog. So if the
softlockup and rcu hang detection traces are not being printed because
the CPU is stuck with interrupts off, then the hard lockup watchdog
should get it with the NMI IPI.

Fixes: 2104180a5369 ("powerpc/64s: implement arch-specific hardlockup watchdog")
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
(cherry picked from commit 47712a921bb781caf69fca9eae43be19968816cb)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
 arch/powerpc/include/asm/nmi.h |  4 ----
 arch/powerpc/kernel/watchdog.c | 22 ----------------------
 2 files changed, 26 deletions(-)

diff --git a/arch/powerpc/include/asm/nmi.h b/arch/powerpc/include/asm/nmi.h
index e97f586..9c80939 100644
--- a/arch/powerpc/include/asm/nmi.h
+++ b/arch/powerpc/include/asm/nmi.h
@@ -4,10 +4,6 @@
 extern void arch_touch_nmi_watchdog(void);
-extern void arch_trigger_cpumask_backtrace(const cpumask_t *mask,
-					   bool exclude_self);
-#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
 static inline void arch_touch_nmi_watchdog(void) {}
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index 87da80c..3963baa 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -393,25 +393,3 @@ int __init watchdog_nmi_probe(void)
 	return 0;
-static void handle_backtrace_ipi(struct pt_regs *regs)
-	nmi_cpu_backtrace(regs);
-static void raise_backtrace_ipi(cpumask_t *mask)
-	unsigned int cpu;
-	for_each_cpu(cpu, mask) {
-		if (cpu == smp_processor_id())
-			handle_backtrace_ipi(NULL);
-		else
-			smp_send_nmi_ipi(cpu, handle_backtrace_ipi, 1000000);
-	}
-void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
-	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi);

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