powerpc: Make decrementer interrupt robust against offlined CPUs

With some implementations, it is possible that a timer interrupt
occurs every few seconds on an offline CPU. In this case, just
re-arm the decrementer and return immediately

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index aa9269600ca21d7cd924acab3a23141cc42f1cbf..375480c56eb9fd6699c90e385dd1877affb3d052 100644 (file)
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -577,14 +577,21 @@ void timer_interrupt(struct pt_regs * regs)
        struct clock_event_device *evt = &decrementer->event;
        u64 now;
 
+       /* Ensure a positive value is written to the decrementer, or else
+        * some CPUs will continue to take decrementer exceptions.
+        */
+       set_dec(DECREMENTER_MAX);
+
+       /* Some implementations of hotplug will get timer interrupts while
+        * offline, just ignore these
+        */
+       if (!cpu_online(smp_processor_id()))
+               return;
+
        trace_timer_interrupt_entry(regs);
 
        __get_cpu_var(irq_stat).timer_irqs++;
 
-       /* Ensure a positive value is written to the decrementer, or else
-        * some CPUs will continuue to take decrementer exceptions */
-       set_dec(DECREMENTER_MAX);
-
 #if defined(CONFIG_PPC32) && defined(CONFIG_PMAC)
        if (atomic_read(&ppc_n_lost_interrupts) != 0)
                do_IRQ(regs);