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SubjectRe: [PATCH v7 2/2] tracing: Add support for preempt and irq enable/disable events
Hi Peter,

On Wed, Oct 4, 2017 at 9:01 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Fri, Sep 29, 2017 at 02:22:45PM -0700, Joel Fernandes wrote:
[...]
>> + */
>> +static DEFINE_PER_CPU(int, tracing_irq_cpu);
>> +
>> #if defined(CONFIG_TRACE_IRQFLAGS) && !defined(CONFIG_PROVE_LOCKING)
>> void trace_hardirqs_on(void)
>> {
>> + if (!this_cpu_read(tracing_irq_cpu))
>> + return;
>> +
>> + trace_irq_enable_rcuidle(CALLER_ADDR0, CALLER_ADDR1);
>> tracer_hardirqs_on();
>> +
>> + this_cpu_write(tracing_irq_cpu, 0);
>> }
>> EXPORT_SYMBOL(trace_hardirqs_on);
>>
>> void trace_hardirqs_off(void)
>> {
>> + if (this_cpu_read(tracing_irq_cpu))
>> + return;
>> +
>> + this_cpu_write(tracing_irq_cpu, 1);
>> +
>> + trace_irq_disable_rcuidle(CALLER_ADDR0, CALLER_ADDR1);
>> tracer_hardirqs_off();
>> }
>> EXPORT_SYMBOL(trace_hardirqs_off);
>>
>> __visible void trace_hardirqs_on_caller(unsigned long caller_addr)
>> {
>> + if (!this_cpu_read(tracing_irq_cpu))
>> + return;
>> +
>> + trace_irq_enable_rcuidle(CALLER_ADDR0, caller_addr);
>> tracer_hardirqs_on_caller(caller_addr);
>> +
>> + this_cpu_write(tracing_irq_cpu, 0);
>> }
>> EXPORT_SYMBOL(trace_hardirqs_on_caller);
>>
>> __visible void trace_hardirqs_off_caller(unsigned long caller_addr)
>> {
>> + if (this_cpu_read(tracing_irq_cpu))
>> + return;
>> +
>> + this_cpu_write(tracing_irq_cpu, 1);
>> +
>> + trace_irq_disable_rcuidle(CALLER_ADDR0, caller_addr);
>> tracer_hardirqs_off_caller(caller_addr);
>> }
>> EXPORT_SYMBOL(trace_hardirqs_off_caller);
>
> lockdep implements the trace_hardirq_*() in terms of *_caller(). Would
> that make sense here?

In lockdep code, when trace_hardirqs_off is called,
trace_hardirqs_off_caller would pass CALLER_ADDR0 as
trace_hardirqs_off.

Because of this, the first argument passed to time_hardirqs_off would
always be an offset within trace_hardirqs_off:
time_hardirqs_off(CALLER_ADDR0, ip);

Is that intended? Seems to me that in the lockdep implementation of
trace_hardirqs_* in terms of *_caller(), we would completely miss the
second-last return address (CALLER_ADDR1) of trace_hardirqs_off().
Also for the above reasons, I don't think it doesn't make sense to use
this reuse logic for the tracer. Atleast I feel it might change the
current behavior of the preempt/irqsoff tracer which I don't intend to
change with my current patch set.

thanks,

- Joel

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