[PATCH 1/3] x86: Only call smp_processor_id in non-preempt cases

[Don Zickus]

There are some paths that walk the die_chain with preemption on.
Make sure we are in an NMI call before we start doing anything.

This was triggered by do_general_protection calling notify_die with
DIE_GPF.

Reported-by: Jan Kiszka <jan.kiszka@xxxxxx>
CC: Jan Kiszka <jan.kiszka@xxxxxx>
Signed-off-by: Don Zickus <dzickus@xxxxxxxxxx>
---
 arch/x86/kernel/apic/hw_nmi.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
index c57d0b5..2b40a60 100644
--- a/arch/x86/kernel/apic/hw_nmi.c
+++ b/arch/x86/kernel/apic/hw_nmi.c
@@ -51,7 +51,7 @@ arch_trigger_all_cpu_backtrace_handler(struct notifier_block *self,
 {
 	struct die_args *args = __args;
 	struct pt_regs *regs;
-	int cpu = smp_processor_id();
+	int cpu;
 
 	switch (cmd) {
 	case DIE_NMI:
@@ -63,6 +63,7 @@ arch_trigger_all_cpu_backtrace_handler(struct notifier_block *self,
 	}
 
 	regs = args->regs;
+	cpu = smp_processor_id();
 
 	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
 		static arch_spinlock_t lock = __ARCH_SPIN_LOCK_UNLOCKED;
-- 
1.7.3.4

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