Re: [PATCH v6 2/2] tracing: Add support for preempt and irq enable/disable events

[Steven Rostedt]

On Mon, 25 Sep 2017 17:23:00 -0700
Joel Fernandes <joe...@google.com> wrote:

> The trace_hardirqs_off API can be called even when IRQs are already
> off. This is unlike the trace_hardirqs_on which checks if IRQs are off
> (atleast from some callsites), here are the definitions just for
> reference [1]. I guess we could modify local_irq_disable and
> local_irq_save to check what the HW flags was before calling
> raw_local_irq_save and only then call trace_hardirqs_off if they were
> indeed on and now being turned off, but that adds complexity to it -
> also we have to then modify all the callsites from assembly code to
> conditionally call trace_hardirqs_on/off :(.
> 

> [1] 
> http://elixir.free-electrons.com/linux/latest/source/include/linux/irqflags.h#L89

Yeah, I think the issue for the recursion is basically this:

#define local_irq_restore(flags)                        \
        do {                                            \
                if (raw_irqs_disabled_flags(flags)) {   \
                        raw_local_irq_restore(flags);   \
                        trace_hardirqs_off();           \
                } else {                                \
                        trace_hardirqs_on();            \
                        raw_local_irq_restore(flags);   \
                }                                       \
        } while (0)


Peter,

Is there any place where we would call local_irq_restore() when
interrupts are enabled?

-- Steve