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x86/tracing: Introduce a static key for exception tracing

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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>
This commit is contained in:
Thomas Gleixner 2017-08-28 08:47:21 +02:00 committed by Ingo Molnar
parent f7eaf6e00f
commit 2feb1b316d
4 changed files with 25 additions and 7 deletions
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15
arch/x86/include/asm/trace/common.h Normal file
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@ -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

4
arch/x86/include/asm/trace/exceptions.h
View File

@ -5,9 +5,7 @@
#define _TRACE_PAGE_FAULT_H #define _TRACE_PAGE_FAULT_H
#include <linux/tracepoint.h> #include <linux/tracepoint.h>
#include <asm/trace/common.h>
extern int trace_irq_vector_regfunc(void);
extern void trace_irq_vector_unregfunc(void);
DECLARE_EVENT_CLASS(x86_exceptions, DECLARE_EVENT_CLASS(x86_exceptions,

4
arch/x86/include/asm/trace/irq_vectors.h
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@ -5,9 +5,7 @@
#define _TRACE_IRQ_VECTORS_H #define _TRACE_IRQ_VECTORS_H
#include <linux/tracepoint.h> #include <linux/tracepoint.h>
#include <asm/trace/common.h>
extern int trace_irq_vector_regfunc(void);
extern void trace_irq_vector_unregfunc(void);
DECLARE_EVENT_CLASS(x86_irq_vector, DECLARE_EVENT_CLASS(x86_irq_vector,

9
arch/x86/kernel/tracepoint.c
View File

@ -4,9 +4,11 @@
* Copyright (C) 2013 Seiji Aguchi <seiji.aguchi@hds.com> * 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/hw_irq.h>
#include <asm/desc.h> #include <asm/desc.h>
#include <linux/atomic.h>
atomic_t trace_idt_ctr = ATOMIC_INIT(0); atomic_t trace_idt_ctr = ATOMIC_INIT(0);
struct desc_ptr trace_idt_descr = { NR_VECTORS * 16 - 1, 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. */ /* 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; gate_desc trace_idt_table[NR_VECTORS] __page_aligned_bss;
DEFINE_STATIC_KEY_FALSE(trace_irqvectors_key);
static int trace_irq_vector_refcount; static int trace_irq_vector_refcount;
static DEFINE_MUTEX(irq_vector_mutex); static DEFINE_MUTEX(irq_vector_mutex);
@ -36,6 +39,8 @@ static void switch_idt(void *arg)
int trace_irq_vector_regfunc(void) int trace_irq_vector_regfunc(void)
{ {
static_branch_inc(&trace_irqvectors_key);
mutex_lock(&irq_vector_mutex); mutex_lock(&irq_vector_mutex);
if (!trace_irq_vector_refcount) { if (!trace_irq_vector_refcount) {
set_trace_idt_ctr(1); set_trace_idt_ctr(1);
@ -49,6 +54,8 @@ int trace_irq_vector_regfunc(void)
void trace_irq_vector_unregfunc(void) void trace_irq_vector_unregfunc(void)
{ {
static_branch_dec(&trace_irqvectors_key);
mutex_lock(&irq_vector_mutex); mutex_lock(&irq_vector_mutex);
trace_irq_vector_refcount--; trace_irq_vector_refcount--;
if (!trace_irq_vector_refcount) { if (!trace_irq_vector_refcount) {