linux-kernel - Re: [PATCH v4 05/27] x86: Replace ist_enter() with nmi

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Date:   Wed, 26 Feb 2020 11:25:09 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Greg KH <gregkh@...uxfoundation.org>, gustavo@...eddedor.com,
        Thomas Gleixner <tglx@...utronix.de>, paulmck@...nel.org,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter()

On Mon, Feb 24, 2020 at 05:02:31PM -0500, Steven Rostedt wrote:
> On Mon, 24 Feb 2020 22:31:39 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > > Just want to confirm that printk_nmi_enter(), lockdep_off(),
> > > and ftrace_nmi_enter() are all marked fully with NOKPROBE.  
> > 
> > *sigh*, right you are, I only looked at notrace, not nokprobe.
> > 
> > In particular the ftrace one is a bit off a mess, let me sort through
> > that.
> 
> ftrace_nmi_enter() has two purposes. One, for archs that need to deal with
> NMIs while they still use stop machine. Although, it appears sh is the only
> arch that does that. I can look to see if it can be ripped out.

Already done  :-)

---
Subject: sh/ftrace: Move arch_ftrace_nmi_{enter,exit} into nmi exception
From: Peter Zijlstra <peterz@...radead.org>
Date: Mon Feb 24 22:26:21 CET 2020

SuperH is the last remaining user of arch_ftrace_nmi_{enter,exit}(),
remove it from the generic code and into the SuperH code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 Documentation/trace/ftrace-design.rst |    8 --------
 arch/sh/Kconfig                       |    1 -
 arch/sh/kernel/traps.c                |   12 ++++++++++++
 include/linux/ftrace_irq.h            |   11 -----------
 kernel/trace/Kconfig                  |   10 ----------
 5 files changed, 12 insertions(+), 30 deletions(-)

--- a/Documentation/trace/ftrace-design.rst
+++ b/Documentation/trace/ftrace-design.rst
@@ -229,14 +229,6 @@ Adding support for it is easy: just defi
 pass the return address pointer as the 'retp' argument to
 ftrace_push_return_trace().
 
-HAVE_FTRACE_NMI_ENTER
----------------------
-
-If you can't trace NMI functions, then skip this option.
-
-<details to be filled>
-
-
 HAVE_SYSCALL_TRACEPOINTS
 ------------------------
 
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -71,7 +71,6 @@ config SUPERH32
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_DYNAMIC_FTRACE
-	select HAVE_FTRACE_NMI_ENTER if DYNAMIC_FTRACE
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_ARCH_KGDB
--- a/arch/sh/kernel/traps.c
+++ b/arch/sh/kernel/traps.c
@@ -170,11 +170,21 @@ BUILD_TRAP_HANDLER(bug)
 	force_sig(SIGTRAP);
 }
 
+#ifdef CONFIG_HAVE_DYNAMIC_FTRACE
+extern void arch_ftrace_nmi_enter(void);
+extern void arch_ftrace_nmi_exit(void);
+#else
+static inline void arch_ftrace_nmi_enter(void) { }
+static inline void arch_ftrace_nmi_exit(void) { }
+#endif
+
 BUILD_TRAP_HANDLER(nmi)
 {
 	unsigned int cpu = smp_processor_id();
 	TRAP_HANDLER_DECL;
 
+	arch_ftrace_nmi_enter();
+
 	nmi_enter();
 	nmi_count(cpu)++;
 
@@ -190,4 +200,6 @@ BUILD_TRAP_HANDLER(nmi)
 	}
 
 	nmi_exit();
+
+	arch_ftrace_nmi_exit();
 }
--- a/include/linux/ftrace_irq.h
+++ b/include/linux/ftrace_irq.h
@@ -2,15 +2,6 @@
 #ifndef _LINUX_FTRACE_IRQ_H
 #define _LINUX_FTRACE_IRQ_H
 
-
-#ifdef CONFIG_FTRACE_NMI_ENTER
-extern void arch_ftrace_nmi_enter(void);
-extern void arch_ftrace_nmi_exit(void);
-#else
-static inline void arch_ftrace_nmi_enter(void) { }
-static inline void arch_ftrace_nmi_exit(void) { }
-#endif
-
 #ifdef CONFIG_HWLAT_TRACER
 extern bool trace_hwlat_callback_enabled;
 extern void trace_hwlat_callback(bool enter);
@@ -22,12 +13,10 @@ static inline void ftrace_nmi_enter(void
 	if (trace_hwlat_callback_enabled)
 		trace_hwlat_callback(true);
 #endif
-	arch_ftrace_nmi_enter();
 }
 
 static inline void ftrace_nmi_exit(void)
 {
-	arch_ftrace_nmi_exit();
 #ifdef CONFIG_HWLAT_TRACER
 	if (trace_hwlat_callback_enabled)
 		trace_hwlat_callback(false);
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -10,11 +10,6 @@ config USER_STACKTRACE_SUPPORT
 config NOP_TRACER
 	bool
 
-config HAVE_FTRACE_NMI_ENTER
-	bool
-	help
-	  See Documentation/trace/ftrace-design.rst
-
 config HAVE_FUNCTION_TRACER
 	bool
 	help
@@ -72,11 +67,6 @@ config RING_BUFFER
 	select TRACE_CLOCK
 	select IRQ_WORK
 
-config FTRACE_NMI_ENTER
-       bool
-       depends on HAVE_FTRACE_NMI_ENTER
-       default y
-
 config EVENT_TRACING
 	select CONTEXT_SWITCH_TRACER
 	select GLOB