linux-kernel - Re: [RESEND][patch V3 05/23] tracing: Provide lockdep less trace_hardirqs

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Message-ID: <322ac9e0-9567-8e7c-e2af-e9e1107717bf@oracle.com>
Date:   Fri, 3 Apr 2020 10:34:56 +0200
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Paul McKenney <paulmck@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [RESEND][patch V3 05/23] tracing: Provide lockdep less
 trace_hardirqs_on/off() variants


On 3/20/20 7:00 PM, Thomas Gleixner wrote:
> trace_hardirqs_on/off() is only partially safe vs. RCU idle. The tracer
> core itself is safe, but the resulting tracepoints can be utilized by
> e.g. BPF which is unsafe.
> 
> Provide variants which do not contain the lockdep invocation so the lockdep
> and tracer invocations can be split at the call site and placed properly.
> 
> The new variants also do not use rcuidle as they are going to be called
> from entry code after/before context tracking.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> V2: New patch
> ---
>   include/linux/irqflags.h        |    4 ++++
>   kernel/trace/trace_preemptirq.c |   23 +++++++++++++++++++++++
>   2 files changed, 27 insertions(+)
> 
> --- a/include/linux/irqflags.h
> +++ b/include/linux/irqflags.h
> @@ -29,6 +29,8 @@
>   #endif
>   
>   #ifdef CONFIG_TRACE_IRQFLAGS
> +  extern void __trace_hardirqs_on(void);
> +  extern void __trace_hardirqs_off(void);
>     extern void trace_hardirqs_on(void);
>     extern void trace_hardirqs_off(void);
>   # define trace_hardirq_context(p)	((p)->hardirq_context)
> @@ -52,6 +54,8 @@ do {						\
>   	current->softirq_context--;		\
>   } while (0)
>   #else
> +# define __trace_hardirqs_on()		do { } while (0)
> +# define __trace_hardirqs_off()		do { } while (0)
>   # define trace_hardirqs_on()		do { } while (0)
>   # define trace_hardirqs_off()		do { } while (0)
>   # define trace_hardirq_context(p)	0
> --- a/kernel/trace/trace_preemptirq.c
> +++ b/kernel/trace/trace_preemptirq.c
> @@ -19,6 +19,17 @@
>   /* Per-cpu variable to prevent redundant calls when IRQs already off */
>   static DEFINE_PER_CPU(int, tracing_irq_cpu);
>   
> +void __trace_hardirqs_on(void)
> +{
> +	if (this_cpu_read(tracing_irq_cpu)) {
> +		if (!in_nmi())
> +			trace_irq_enable(CALLER_ADDR0, CALLER_ADDR1);
> +		tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
> +		this_cpu_write(tracing_irq_cpu, 0);
> +	}
> +}
> +NOKPROBE_SYMBOL(__trace_hardirqs_on);
> +

It would be good to have a comment which highlights the difference between
__trace_hardirqs_on/off and trace_hardirqs_on/off because the code difference
is not obvious and the function names are so similar.

alex.

>   void trace_hardirqs_on(void)
>   {
>   	if (this_cpu_read(tracing_irq_cpu)) {
> @@ -33,6 +44,18 @@ void trace_hardirqs_on(void)
>   EXPORT_SYMBOL(trace_hardirqs_on);
>   NOKPROBE_SYMBOL(trace_hardirqs_on);
>   
> +void __trace_hardirqs_off(void)
> +{
> +	if (!this_cpu_read(tracing_irq_cpu)) {
> +		this_cpu_write(tracing_irq_cpu, 1);
> +		tracer_hardirqs_off(CALLER_ADDR0, CALLER_ADDR1);
> +		if (!in_nmi())
> +			trace_irq_disable(CALLER_ADDR0, CALLER_ADDR1);
> +	}
> +
> +}
> +NOKPROBE_SYMBOL(__trace_hardirqs_off);
> +
>   void trace_hardirqs_off(void)
>   {
>   	if (!this_cpu_read(tracing_irq_cpu)) {
>