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

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Date:   Sat, 30 Sep 2017 05:08:17 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com
Subject: Re: [PATCH v6 2/2] tracing: Add support for preempt and irq
 enable/disable events

On Mon, 25 Sep 2017 17:23:00 -0700
Joel Fernandes <joelaf@...gle.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