Re: [RFC PATCH 5/5] arm: perf: Use FIQ to handle PMU events.

On Tue, Jan 13, 2015 at 04:35:31PM +0000, Daniel Thompson wrote:

+/*

• • This handler is called *unconditionally* from the default NMI/FIQ
• • handler. The irq may not be anything to do with us so the main
• • job of this function is to figure out if the irq passed in is ours
• • or not.
• */

+void cpu_pmu_handle_fiq(int irq) +{

• int cpu = smp_processor_id();

This can be either debug_smp_processor_id() or raw_smp_processor_id(). raw_smp_processor_id() is fine from FIQ contexts, as seems to be debug_smp_processor_id(), but only because we guarantee that irqs_disabled() in there will be true.

• if (irq != get_cpu_var(cpu_pmu_irqs))

• return;
  

get_cpu_var() needs put_cpu_var() to undo its effects. get_cpu_var() calls preempt_disable(), which calls into lockdep... I think we determined that was fine last time we went digging? put_cpu_var() would call preempt_enable() which I'd hope would be safe in FIQ/NMI contexts?

• (void)armpmu_dispatch_irq(irq,

• 		  get_cpu_ptr(&cpu_pmu->hw_events->percpu_pmu));
  

Again, get_cpu_xxx() needs to be balanced with a put_cpu_xxx().