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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	mingo@kernel.org, joel@joelfernandes.org,
	gregkh@linuxfoundation.org, gustavo@embeddedor.com,
	tglx@linutronix.de, josh@joshtriplett.org,
	mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
	luto@kernel.org, tony.luck@intel.com, frederic@kernel.org,
	dan.carpenter@oracle.com, mhiramat@kernel.org
Subject: Re: [PATCH v3 08/22] rcu,tracing: Create trace_rcu_{enter,exit}()
Date: Thu, 20 Feb 2020 05:58:00 -0800	[thread overview]
Message-ID: <20200220135800.GT2935@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200220103421.GV18400@hirez.programming.kicks-ass.net>

On Thu, Feb 20, 2020 at 11:34:21AM +0100, Peter Zijlstra wrote:
> On Wed, Feb 19, 2020 at 08:44:50AM -0800, Paul E. McKenney wrote:
> > On Wed, Feb 19, 2020 at 05:35:35PM +0100, Peter Zijlstra wrote:
> 
> > > Possibly, and I suppose the current version is less obviously dependent
> > > on the in_nmi() functionality as was the previous, seeing how Paul
> > > frobbed that all the way into the rcu_irq_enter*() implementation.
> > > 
> > > So sure, I can go move it I suppose.
> > 
> > No objections here.
> 
> It now looks like so:
> 
> ---
> Subject: rcu,tracing: Create trace_rcu_{enter,exit}()
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Wed Feb 12 09:18:57 CET 2020
> 
> To facilitate tracers that need RCU, add some helpers to wrap the
> magic required.
> 
> The problem is that we can call into tracers (trace events and
> function tracing) while RCU isn't watching and this can happen from
> any context, including NMI.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  include/linux/rcupdate.h |   29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -175,6 +175,35 @@ do { \
>  #error "Unknown RCU implementation specified to kernel configuration"
>  #endif
>  
> +/**
> + * trace_rcu_enter - Force RCU to be active, for code that needs RCU readers
> + *
> + * Very similar to RCU_NONIDLE() above.
> + *
> + * Tracing can happen while RCU isn't active yet, for instance in the idle loop
> + * between rcu_idle_enter() and rcu_idle_exit(), or early in exception entry.
> + * RCU will happily ignore any read-side critical sections in this case.
> + *
> + * This function ensures that RCU is aware hereafter and the code can readily
> + * rely on RCU read-side critical sections working as expected.
> + *
> + * This function is NMI safe -- provided in_nmi() is correct and will nest up-to
> + * INT_MAX/2 times.
> + */
> +static inline int trace_rcu_enter(void)
> +{
> +	int state = !rcu_is_watching();
> +	if (state)
> +		rcu_irq_enter_irqsave();
> +	return state;
> +}
> +
> +static inline void trace_rcu_exit(int state)
> +{
> +	if (state)
> +		rcu_irq_exit_irqsave();
> +}
> +
>  /*
>   * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
>   * are needed for dynamic initialization and destruction of rcu_head

  reply	other threads:[~2020-02-20 13:58 UTC|newest]

Thread overview: 99+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-19 14:47 [PATCH v3 00/22] tracing vs world Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 01/22] hardirq/nmi: Allow nested nmi_enter() Peter Zijlstra
2020-02-19 15:31   ` Steven Rostedt
2020-02-19 16:56     ` Borislav Petkov
2020-02-19 17:07       ` Peter Zijlstra
2020-02-20  8:41   ` Will Deacon
2020-02-20  9:19   ` Marc Zyngier
2020-02-20 13:18   ` Petr Mladek
2020-02-19 14:47 ` [PATCH v3 02/22] x86,mce: Delete ist_begin_non_atomic() Peter Zijlstra
2020-02-19 17:13   ` Borislav Petkov
2020-02-19 17:21     ` Andy Lutomirski
2020-02-19 17:33       ` Peter Zijlstra
2020-02-19 22:12         ` Andy Lutomirski
2020-02-19 22:33           ` Luck, Tony
2020-02-19 22:48             ` Andy Lutomirski
2020-02-20  7:39           ` Peter Zijlstra
2020-02-19 17:42       ` Borislav Petkov
2020-02-19 17:46         ` Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 03/22] x86: Replace ist_enter() with nmi_enter() Peter Zijlstra
2020-02-20 10:54   ` Borislav Petkov
2020-02-20 12:11     ` Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 04/22] x86/doublefault: Make memmove() notrace/NOKPROBE Peter Zijlstra
2020-02-19 15:36   ` Steven Rostedt
2020-02-19 15:40     ` Peter Zijlstra
2020-02-19 15:55       ` Steven Rostedt
2020-02-19 15:57       ` Peter Zijlstra
2020-02-19 16:04         ` Peter Zijlstra
2020-02-19 16:12           ` Steven Rostedt
2020-02-19 16:27             ` Paul E. McKenney
2020-02-19 16:34               ` Peter Zijlstra
2020-02-19 16:46                 ` Paul E. McKenney
2020-02-19 17:05               ` Steven Rostedt
2020-02-20 12:17         ` Borislav Petkov
2020-02-20 12:37           ` Peter Zijlstra
2020-02-19 15:47   ` Steven Rostedt
2020-02-19 14:47 ` [PATCH v3 05/22] rcu: Make RCU IRQ enter/exit functions rely on in_nmi() Peter Zijlstra
2020-02-19 16:31   ` Paul E. McKenney
2020-02-19 16:37     ` Peter Zijlstra
2020-02-19 16:45       ` Paul E. McKenney
2020-02-19 17:03       ` Peter Zijlstra
2020-02-19 17:42         ` Paul E. McKenney
2020-02-19 17:16     ` [PATCH] rcu/kprobes: Comment why rcu_nmi_enter() is marked NOKPROBE Steven Rostedt
2020-02-19 17:18       ` Joel Fernandes
2020-02-19 17:41       ` Paul E. McKenney
2020-02-20  5:54       ` Masami Hiramatsu
2020-02-19 14:47 ` [PATCH v3 06/22] rcu: Rename rcu_irq_{enter,exit}_irqson() Peter Zijlstra
2020-02-19 16:38   ` Paul E. McKenney
2020-02-19 14:47 ` [PATCH v3 07/22] rcu: Mark rcu_dynticks_curr_cpu_in_eqs() inline Peter Zijlstra
2020-02-19 16:39   ` Paul E. McKenney
2020-02-19 17:19     ` Steven Rostedt
2020-02-19 14:47 ` [PATCH v3 08/22] rcu,tracing: Create trace_rcu_{enter,exit}() Peter Zijlstra
2020-02-19 15:49   ` Steven Rostedt
2020-02-19 15:58     ` Peter Zijlstra
2020-02-19 16:15       ` Steven Rostedt
2020-02-19 16:35         ` Peter Zijlstra
2020-02-19 16:44           ` Paul E. McKenney
2020-02-20 10:34             ` Peter Zijlstra
2020-02-20 13:58               ` Paul E. McKenney [this message]
2020-02-19 14:47 ` [PATCH v3 09/22] sched,rcu,tracing: Avoid tracing before in_nmi() is correct Peter Zijlstra
2020-02-19 15:50   ` Steven Rostedt
2020-02-19 15:50   ` Steven Rostedt
2020-02-19 14:47 ` [PATCH v3 10/22] x86,tracing: Add comments to do_nmi() Peter Zijlstra
2020-02-19 15:51   ` Steven Rostedt
2020-02-19 14:47 ` [PATCH v3 11/22] perf,tracing: Prepare the perf-trace interface for RCU changes Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 12/22] tracing: Employ trace_rcu_{enter,exit}() Peter Zijlstra
2020-02-19 15:52   ` Steven Rostedt
2020-02-19 14:47 ` [PATCH v3 13/22] tracing: Remove regular RCU context for _rcuidle tracepoints (again) Peter Zijlstra
2020-02-19 15:53   ` Steven Rostedt
2020-02-19 16:43   ` Paul E. McKenney
2020-02-19 16:47     ` Peter Zijlstra
2020-02-19 17:05       ` Peter Zijlstra
2020-02-19 17:21         ` Steven Rostedt
2020-02-19 17:40           ` Paul E. McKenney
2020-02-19 18:00             ` Steven Rostedt
2020-02-19 19:05               ` Paul E. McKenney
2020-02-19 14:47 ` [PATCH v3 14/22] perf,tracing: Allow function tracing when !RCU Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 15/22] x86/int3: Ensure that poke_int3_handler() is not traced Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 16/22] locking/atomics, kcsan: Add KCSAN instrumentation Peter Zijlstra
2020-02-19 15:46   ` Steven Rostedt
2020-02-19 16:03     ` Peter Zijlstra
2020-02-19 16:50       ` Paul E. McKenney
2020-02-19 16:54         ` Peter Zijlstra
2020-02-19 17:36           ` Paul E. McKenney
2020-02-19 14:47 ` [PATCH v3 17/22] asm-generic/atomic: Use __always_inline for pure wrappers Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 18/22] asm-generic/atomic: Use __always_inline for fallback wrappers Peter Zijlstra
2020-02-19 16:55   ` Paul E. McKenney
2020-02-19 17:06     ` Peter Zijlstra
2020-02-19 17:35       ` Paul E. McKenney
2020-02-19 14:47 ` [PATCH v3 19/22] compiler: Simple READ/WRITE_ONCE() implementations Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 20/22] locking/atomics: Flip fallbacks and instrumentation Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 21/22] x86/int3: Avoid atomic instrumentation Peter Zijlstra
2020-02-19 14:47 ` [PATCH v3 22/22] x86/int3: Ensure that poke_int3_handler() is not sanitized Peter Zijlstra
2020-02-19 16:06   ` Dmitry Vyukov
2020-02-19 16:30     ` Peter Zijlstra
2020-02-19 16:51       ` Peter Zijlstra
2020-02-19 17:20       ` Peter Zijlstra
2020-02-20 10:37         ` Dmitry Vyukov
2020-02-20 12:06           ` Peter Zijlstra
2020-02-20 16:22             ` Dmitry Vyukov

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