linux-kernel - Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage

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Date:   Tue, 07 Aug 2018 10:48:05 -0400
From:   Joel Fernandes <joelaf@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     Joel Fernandes <joel@...lfernandes.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Glexiner <tglx@...utronix.de>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>
Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage



On August 7, 2018 10:34:10 AM EDT, Steven Rostedt <rostedt@...dmis.org> wrote:
>On Tue, 07 Aug 2018 10:10:59 -0400
>Joel Fernandes <joelaf@...gle.com> wrote:
>
>> On August 7, 2018 9:49:54 AM EDT, Steven Rostedt
><rostedt@...dmis.org> wrote:
>> >On Tue, 7 Aug 2018 06:33:35 -0700
>> >Joel Fernandes <joelaf@...gle.com> wrote:
>> >  
>> >> Thanks, also one more thing I noticed in your patch,
>> >> lockdep_hardirqs_off needs to be called before all other probes
>but
>> >> you're calling it after. This is why I registered it with INT_MAX:
>> >> 
>> >> register_trace_prio_irq_disable(lockdep_hardirqs_off, NULL,
>INT_MAX);
>> >> 
>> >> Without it you may get annotation warnings. Thanks,  
>> >
>> >Interesting. I was following the old way where we called the tracing
>> >code before calling the lockdep code (all hard coded and not from
>> >trace events). Is this have something to do with calling the code
>from
>> >a tracepoint?
>> >
>> >Do you have an example that could trigger the warning?
>> >  
>> 
>> I remember the warnings but can't remember now how I triggered them.
>> I think I saw them with the irqsoff tracer or irq trace events
>> running, with lockdep turned on.
>
>I'll see if I can trigger it. I'll run this all through my tests.

Ok.

>> Also an irq disable probe that does a lockdep assert that irqs are
>> disabled could trigger it?
>> 
>
>You mean if someone add a tracepoint callback to the irq disable
>tracepoint, and did a lockdep assert to make sure interrupts are
>disabled?

Yes that's what I meant.

Thanks,

- Joel

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