Re: [PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter()

From: Masami Hiramatsu <mhiramat@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Andy Lutomirski <luto@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Joel Fernandes <joel@joelfernandes.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	gustavo@embeddedor.com, Thomas Gleixner <tglx@linutronix.de>,
	paulmck@kernel.org, Josh Triplett <josh@joshtriplett.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Tony Luck <tony.luck@intel.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter()
Date: Sat, 7 Mar 2020 10:53:45 +0900	[thread overview]
Message-ID: <20200307105345.e33c2ced6d1f020e1bf91018@kernel.org> (raw)
In-Reply-To: <20200226102758.GV18400@hirez.programming.kicks-ass.net>

Hi Peter,

On Wed, 26 Feb 2020 11:27:58 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, Feb 24, 2020 at 05:02:31PM -0500, Steven Rostedt wrote:
> 
> > The other is for the hwlat detector that measures the time it was in an
> > NMI, as NMIs appear as a hardware latency too.
> 
> Yeah,.. I hate that one. But I ended up with this patch.
> 
> And yes, I know some of those notrace annotations are strictly
> unnessecary due to Makefile crap, but having them is _SO_ much easier.
> 
> ---
> Subject: x86,tracing: Robustify ftrace_nmi_enter()
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Mon Feb 24 23:40:29 CET 2020
> 
>   ftrace_nmi_enter()
>      trace_hwlat_callback()
>        trace_clock_local()
>          sched_clock()
>            paravirt_sched_clock()
>            native_sched_clock()
> 
> All must not be traced or kprobed, it will be called from do_debug()
> before the kprobe handler.

As I found today, we need to make NOKPROBE on exit side too, and this
covers exit side.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you,

> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  arch/x86/include/asm/paravirt.h |    2 +-
>  arch/x86/kernel/tsc.c           |    7 +++++--
>  include/linux/ftrace_irq.h      |    4 ++--
>  kernel/trace/trace_clock.c      |    2 ++
>  kernel/trace/trace_hwlat.c      |    4 +++-
>  5 files changed, 13 insertions(+), 6 deletions(-)
> 
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -17,7 +17,7 @@
>  #include <linux/cpumask.h>
>  #include <asm/frame.h>
>  
> -static inline unsigned long long paravirt_sched_clock(void)
> +static __always_inline unsigned long long paravirt_sched_clock(void)
>  {
>  	return PVOP_CALL0(unsigned long long, time.sched_clock);
>  }
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -14,6 +14,7 @@
>  #include <linux/percpu.h>
>  #include <linux/timex.h>
>  #include <linux/static_key.h>
> +#include <linux/kprobes.h>
>  
>  #include <asm/hpet.h>
>  #include <asm/timer.h>
> @@ -207,7 +208,7 @@ static void __init cyc2ns_init_secondary
>  /*
>   * Scheduler clock - returns current time in nanosec units.
>   */
> -u64 native_sched_clock(void)
> +notrace u64 native_sched_clock(void)
>  {
>  	if (static_branch_likely(&__use_tsc)) {
>  		u64 tsc_now = rdtsc();
> @@ -228,6 +229,7 @@ u64 native_sched_clock(void)
>  	/* No locking but a rare wrong value is not a big deal: */
>  	return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
>  }
> +NOKPROBE_SYMBOL(native_sched_clock);
>  
>  /*
>   * Generate a sched_clock if you already have a TSC value.
> @@ -240,10 +242,11 @@ u64 native_sched_clock_from_tsc(u64 tsc)
>  /* We need to define a real function for sched_clock, to override the
>     weak default version */
>  #ifdef CONFIG_PARAVIRT
> -unsigned long long sched_clock(void)
> +notrace unsigned long long sched_clock(void)
>  {
>  	return paravirt_sched_clock();
>  }
> +NOKPROBE_SYMBOL(sched_clock);
>  
>  bool using_native_sched_clock(void)
>  {
> --- a/include/linux/ftrace_irq.h
> +++ b/include/linux/ftrace_irq.h
> @@ -7,7 +7,7 @@ extern bool trace_hwlat_callback_enabled
>  extern void trace_hwlat_callback(bool enter);
>  #endif
>  
> -static inline void ftrace_nmi_enter(void)
> +static __always_inline void ftrace_nmi_enter(void)
>  {
>  #ifdef CONFIG_HWLAT_TRACER
>  	if (trace_hwlat_callback_enabled)
> @@ -15,7 +15,7 @@ static inline void ftrace_nmi_enter(void
>  #endif
>  }
>  
> -static inline void ftrace_nmi_exit(void)
> +static __always_inline void ftrace_nmi_exit(void)
>  {
>  #ifdef CONFIG_HWLAT_TRACER
>  	if (trace_hwlat_callback_enabled)
> --- a/kernel/trace/trace_clock.c
> +++ b/kernel/trace/trace_clock.c
> @@ -22,6 +22,7 @@
>  #include <linux/sched/clock.h>
>  #include <linux/ktime.h>
>  #include <linux/trace_clock.h>
> +#include <linux/kprobes.h>
>  
>  /*
>   * trace_clock_local(): the simplest and least coherent tracing clock.
> @@ -44,6 +45,7 @@ u64 notrace trace_clock_local(void)
>  
>  	return clock;
>  }
> +NOKPROBE_SYMBOL(trace_clock_local);
>  EXPORT_SYMBOL_GPL(trace_clock_local);
>  
>  /*
> --- a/kernel/trace/trace_hwlat.c
> +++ b/kernel/trace/trace_hwlat.c
> @@ -43,6 +43,7 @@
>  #include <linux/cpumask.h>
>  #include <linux/delay.h>
>  #include <linux/sched/clock.h>
> +#include <linux/kprobes.h>
>  #include "trace.h"
>  
>  static struct trace_array	*hwlat_trace;
> @@ -137,7 +138,7 @@ static void trace_hwlat_sample(struct hw
>  #define init_time(a, b)	(a = b)
>  #define time_u64(a)	a
>  
> -void trace_hwlat_callback(bool enter)
> +notrace void trace_hwlat_callback(bool enter)
>  {
>  	if (smp_processor_id() != nmi_cpu)
>  		return;
> @@ -156,6 +157,7 @@ void trace_hwlat_callback(bool enter)
>  	if (enter)
>  		nmi_count++;
>  }
> +NOKPROBE_SYMBOL(trace_hwlat_callback);
>  
>  /**
>   * get_sample - sample the CPU TSC and look for likely hardware latencies

-- 
Masami Hiramatsu <mhiramat@kernel.org>