Re: [RESEND][patch V3 05/23] tracing: Provide lockdep less trace_hardirqs_on/off() variants

From: Alexandre Chartre <alexandre.chartre@oracle.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, Paul McKenney <paulmck@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Brian Gerst <brgerst@gmail.com>, Juergen Gross <jgross@suse.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	kvm@vger.kernel.org
Subject: Re: [RESEND][patch V3 05/23] tracing: Provide lockdep less trace_hardirqs_on/off() variants
Date: Fri, 3 Apr 2020 10:34:56 +0200	[thread overview]
Message-ID: <322ac9e0-9567-8e7c-e2af-e9e1107717bf@oracle.com> (raw)
In-Reply-To: <20200320180032.895128936@linutronix.de>

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@linutronix.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)) {
> 