Hot-plugging with CONFIG_DEBUG_PREEMPT=y on a device with arm
architected timers causes a slew of "using smp_processor_id() in
preemptible" warnings:
BUG: using smp_processor_id() in preemptible [00000000] code: sh/111
caller is arch_timer_cpu_notify+0x14/0xc8
This happens because sometimes the cpu notifier,
arch_timer_cpu_notify(), is called in preemptible context and
other times in non-preemptible context but we use this_cpu_ptr()
to retrieve the clockevent in all cases. We're only going to
actually use the pointer in non-preemptible context though, so
push the this_cpu_ptr() access down into the cases to force the
checks to occur only in non-preemptible contexts.
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Acked-by: Marc Zyngier <Marc.Zyngier@xxxxxxx>
Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
---
Resending to arm-soc maintainers instead of timekeeping maintainers. Who
maintains this driver?
drivers/clocksource/arm_arch_timer.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index d7ad425..a65a710 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -248,14 +248,16 @@ static void __cpuinit arch_timer_stop(struct clock_event_device *clk)
static int __cpuinit arch_timer_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
- struct clock_event_device *evt = this_cpu_ptr(arch_timer_evt);
-
+ /*
+ * Grab cpu pointer in each case to avoid spurious
+ * preemptible warnings
+ */
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_STARTING:
- arch_timer_setup(evt);
+ arch_timer_setup(this_cpu_ptr(arch_timer_evt));
break;
case CPU_DYING:
- arch_timer_stop(evt);
+ arch_timer_stop(this_cpu_ptr(arch_timer_evt));
break;
}
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