[tip:x86/apic] x86/tracing: Introduce a static key for exception tracing

tip-bot for Thomas Gleixner
2017-08-29T11:10:57Z

Commit-ID: 2feb1b316d48004d905278c02a55902cab0be8be
Gitweb: http://git.kernel.org/tip/2feb1b316d48004d905278c02a55902cab0be8be
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Mon, 28 Aug 2017 08:47:21 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 29 Aug 2017 11:42:23 +0200

x86/tracing: Introduce a static key for exception tracing

Switching the IDT just for avoiding tracepoints creates a completely
impenetrable macro/inline/ifdef mess.

There is no point in avoiding tracepoints for most of the traps/exceptions.
For the more expensive tracepoints, like pagefaults, this can be handled with
an explicit static key.

Preparatory patch to remove the tracing IDT.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170828064956.593094539@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/trace/common.h | 15 +++++++++++++++
arch/x86/include/asm/trace/exceptions.h | 4 +---
arch/x86/include/asm/trace/irq_vectors.h | 4 +---
arch/x86/kernel/tracepoint.c | 9 ++++++++-
4 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/trace/common.h b/arch/x86/include/asm/trace/common.h
new file mode 100644
index 0000000..b1eb7b1
--- /dev/null
+++ b/arch/x86/include/asm/trace/common.h
@@ -0,0 +1,15 @@
+#ifndef _ASM_TRACE_COMMON_H
+#define _ASM_TRACE_COMMON_H
+
+extern int trace_irq_vector_regfunc(void);
+extern void trace_irq_vector_unregfunc(void);
+
+#ifdef CONFIG_TRACING
+DECLARE_STATIC_KEY_FALSE(trace_irqvectors_key);
+#define trace_irqvectors_enabled() \
+ static_branch_unlikely(&trace_irqvectors_key)
+#else
+static inline bool trace_irqvectors_enabled(void) { return false; }
+#endif
+
+#endif
diff --git a/arch/x86/include/asm/trace/exceptions.h b/arch/x86/include/asm/trace/exceptions.h
index 2422b14..960a5b5 100644
--- a/arch/x86/include/asm/trace/exceptions.h
+++ b/arch/x86/include/asm/trace/exceptions.h
@@ -5,9 +5,7 @@
#define _TRACE_PAGE_FAULT_H

#include <linux/tracepoint.h>
-
-extern int trace_irq_vector_regfunc(void);
-extern void trace_irq_vector_unregfunc(void);
+#include <asm/trace/common.h>

DECLARE_EVENT_CLASS(x86_exceptions,

diff --git a/arch/x86/include/asm/trace/irq_vectors.h b/arch/x86/include/asm/trace/irq_vectors.h
index 32dd6a9..7825b44 100644
--- a/arch/x86/include/asm/trace/irq_vectors.h
+++ b/arch/x86/include/asm/trace/irq_vectors.h
@@ -5,9 +5,7 @@
#define _TRACE_IRQ_VECTORS_H

#include <linux/tracepoint.h>
-
-extern int trace_irq_vector_regfunc(void);
-extern void trace_irq_vector_unregfunc(void);
+#include <asm/trace/common.h>

DECLARE_EVENT_CLASS(x86_irq_vector,

diff --git a/arch/x86/kernel/tracepoint.c b/arch/x86/kernel/tracepoint.c
index 1551513..dd4aa04 100644
--- a/arch/x86/kernel/tracepoint.c
+++ b/arch/x86/kernel/tracepoint.c
@@ -4,9 +4,11 @@
* Copyright (C) 2013 Seiji Aguchi <seiji.aguchi@hds.com>
*
*/
+#include <linux/jump_label.h>
+#include <linux/atomic.h>
+
#include <asm/hw_irq.h>
#include <asm/desc.h>
-#include <linux/atomic.h>

atomic_t trace_idt_ctr = ATOMIC_INIT(0);
struct desc_ptr trace_idt_descr = { NR_VECTORS * 16 - 1,
@@ -15,6 +17,7 @@ struct desc_ptr trace_idt_descr = { NR_VECTORS * 16 - 1,
/* No need to be aligned, but done to keep all IDTs defined the same way. */
gate_desc trace_idt_table[NR_VECTORS] __page_aligned_bss;

+DEFINE_STATIC_KEY_FALSE(trace_irqvectors_key);
static int trace_irq_vector_refcount;
static DEFINE_MUTEX(irq_vector_mutex);

@@ -36,6 +39,8 @@ static void switch_idt(void *arg)

int trace_irq_vector_regfunc(void)
{
+ static_branch_inc(&trace_irqvectors_key);
+
mutex_lock(&irq_vector_mutex);
if (!trace_irq_vector_refcount) {
set_trace_idt_ctr(1);
@@ -49,6 +54,8 @@ int trace_irq_vector_regfunc(void)

void trace_irq_vector_unregfunc(void)
{
+ static_branch_dec(&trace_irqvectors_key);
+
mutex_lock(&irq_vector_mutex);
trace_irq_vector_refcount--;
if (!trace_irq_vector_refcount) {