Commit fc537766 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Ingo Molnar

tracing: Remove markers

Now that the last users of markers have migrated to the event
tracer we can kill off the (now orphan) support code.
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Acked-by: default avatarMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20090917173527.GA1699@lst.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent df58bee2
Using the Linux Kernel Markers
Mathieu Desnoyers
This document introduces Linux Kernel Markers and their use. It provides
examples of how to insert markers in the kernel and connect probe functions to
them and provides some examples of probe functions.
* Purpose of markers
A marker placed in code provides a hook to call a function (probe) that you can
provide at runtime. A marker can be "on" (a probe is connected to it) or "off"
(no probe is attached). When a marker is "off" it has no effect, except for
adding a tiny time penalty (checking a condition for a branch) and space
penalty (adding a few bytes for the function call at the end of the
instrumented function and adds a data structure in a separate section). When a
marker is "on", the function you provide is called each time the marker is
executed, in the execution context of the caller. When the function provided
ends its execution, it returns to the caller (continuing from the marker site).
You can put markers at important locations in the code. Markers are
lightweight hooks that can pass an arbitrary number of parameters,
described in a printk-like format string, to the attached probe function.
They can be used for tracing and performance accounting.
* Usage
In order to use the macro trace_mark, you should include linux/marker.h.
#include <linux/marker.h>
And,
trace_mark(subsystem_event, "myint %d mystring %s", someint, somestring);
Where :
- subsystem_event is an identifier unique to your event
- subsystem is the name of your subsystem.
- event is the name of the event to mark.
- "myint %d mystring %s" is the formatted string for the serializer. "myint" and
"mystring" are repectively the field names associated with the first and
second parameter.
- someint is an integer.
- somestring is a char pointer.
Connecting a function (probe) to a marker is done by providing a probe (function
to call) for the specific marker through marker_probe_register() and can be
activated by calling marker_arm(). Marker deactivation can be done by calling
marker_disarm() as many times as marker_arm() has been called. Removing a probe
is done through marker_probe_unregister(); it will disarm the probe.
marker_synchronize_unregister() must be called between probe unregistration and
the first occurrence of
- the end of module exit function,
to make sure there is no caller left using the probe;
- the free of any resource used by the probes,
to make sure the probes wont be accessing invalid data.
This, and the fact that preemption is disabled around the probe call, make sure
that probe removal and module unload are safe. See the "Probe example" section
below for a sample probe module.
The marker mechanism supports inserting multiple instances of the same marker.
Markers can be put in inline functions, inlined static functions, and
unrolled loops as well as regular functions.
The naming scheme "subsystem_event" is suggested here as a convention intended
to limit collisions. Marker names are global to the kernel: they are considered
as being the same whether they are in the core kernel image or in modules.
Conflicting format strings for markers with the same name will cause the markers
to be detected to have a different format string not to be armed and will output
a printk warning which identifies the inconsistency:
"Format mismatch for probe probe_name (format), marker (format)"
Another way to use markers is to simply define the marker without generating any
function call to actually call into the marker. This is useful in combination
with tracepoint probes in a scheme like this :
void probe_tracepoint_name(unsigned int arg1, struct task_struct *tsk);
DEFINE_MARKER_TP(marker_eventname, tracepoint_name, probe_tracepoint_name,
"arg1 %u pid %d");
notrace void probe_tracepoint_name(unsigned int arg1, struct task_struct *tsk)
{
struct marker *marker = &GET_MARKER(kernel_irq_entry);
/* write data to trace buffers ... */
}
* Probe / marker example
See the example provided in samples/markers/src
Compile them with your kernel.
Run, as root :
modprobe marker-example (insmod order is not important)
modprobe probe-example
cat /proc/marker-example (returns an expected error)
rmmod marker-example probe-example
dmesg
......@@ -29,7 +29,6 @@
#include <linux/poll.h>
#include <linux/ptrace.h>
#include <linux/seq_file.h>
#include <linux/marker.h>
#include <asm/io.h>
#include <asm/time.h>
......
......@@ -39,7 +39,6 @@
#include <linux/pid_namespace.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/marker.h>
#include <asm/io.h>
#include <asm/mmu_context.h>
......
......@@ -15,7 +15,6 @@
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/preempt.h>
#include <linux/marker.h>
#include <linux/msi.h>
#include <asm/signal.h>
......
#ifndef _LINUX_MARKER_H
#define _LINUX_MARKER_H
/*
* Code markup for dynamic and static tracing.
*
* See Documentation/marker.txt.
*
* (C) Copyright 2006 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
*
* This file is released under the GPLv2.
* See the file COPYING for more details.
*/
#include <stdarg.h>
#include <linux/types.h>
struct module;
struct marker;
/**
* marker_probe_func - Type of a marker probe function
* @probe_private: probe private data
* @call_private: call site private data
* @fmt: format string
* @args: variable argument list pointer. Use a pointer to overcome C's
* inability to pass this around as a pointer in a portable manner in
* the callee otherwise.
*
* Type of marker probe functions. They receive the mdata and need to parse the
* format string to recover the variable argument list.
*/
typedef void marker_probe_func(void *probe_private, void *call_private,
const char *fmt, va_list *args);
struct marker_probe_closure {
marker_probe_func *func; /* Callback */
void *probe_private; /* Private probe data */
};
struct marker {
const char *name; /* Marker name */
const char *format; /* Marker format string, describing the
* variable argument list.
*/
char state; /* Marker state. */
char ptype; /* probe type : 0 : single, 1 : multi */
/* Probe wrapper */
void (*call)(const struct marker *mdata, void *call_private, ...);
struct marker_probe_closure single;
struct marker_probe_closure *multi;
const char *tp_name; /* Optional tracepoint name */
void *tp_cb; /* Optional tracepoint callback */
} __attribute__((aligned(8)));
#ifdef CONFIG_MARKERS
#define _DEFINE_MARKER(name, tp_name_str, tp_cb, format) \
static const char __mstrtab_##name[] \
__attribute__((section("__markers_strings"))) \
= #name "\0" format; \
static struct marker __mark_##name \
__attribute__((section("__markers"), aligned(8))) = \
{ __mstrtab_##name, &__mstrtab_##name[sizeof(#name)], \
0, 0, marker_probe_cb, { __mark_empty_function, NULL},\
NULL, tp_name_str, tp_cb }
#define DEFINE_MARKER(name, format) \
_DEFINE_MARKER(name, NULL, NULL, format)
#define DEFINE_MARKER_TP(name, tp_name, tp_cb, format) \
_DEFINE_MARKER(name, #tp_name, tp_cb, format)
/*
* Note : the empty asm volatile with read constraint is used here instead of a
* "used" attribute to fix a gcc 4.1.x bug.
* Make sure the alignment of the structure in the __markers section will
* not add unwanted padding between the beginning of the section and the
* structure. Force alignment to the same alignment as the section start.
*
* The "generic" argument controls which marker enabling mechanism must be used.
* If generic is true, a variable read is used.
* If generic is false, immediate values are used.
*/
#define __trace_mark(generic, name, call_private, format, args...) \
do { \
DEFINE_MARKER(name, format); \
__mark_check_format(format, ## args); \
if (unlikely(__mark_##name.state)) { \
(*__mark_##name.call) \
(&__mark_##name, call_private, ## args);\
} \
} while (0)
#define __trace_mark_tp(name, call_private, tp_name, tp_cb, format, args...) \
do { \
void __check_tp_type(void) \
{ \
register_trace_##tp_name(tp_cb); \
} \
DEFINE_MARKER_TP(name, tp_name, tp_cb, format); \
__mark_check_format(format, ## args); \
(*__mark_##name.call)(&__mark_##name, call_private, \
## args); \
} while (0)
extern void marker_update_probe_range(struct marker *begin,
struct marker *end);
#define GET_MARKER(name) (__mark_##name)
#else /* !CONFIG_MARKERS */
#define DEFINE_MARKER(name, tp_name, tp_cb, format)
#define __trace_mark(generic, name, call_private, format, args...) \
__mark_check_format(format, ## args)
#define __trace_mark_tp(name, call_private, tp_name, tp_cb, format, args...) \
do { \
void __check_tp_type(void) \
{ \
register_trace_##tp_name(tp_cb); \
} \
__mark_check_format(format, ## args); \
} while (0)
static inline void marker_update_probe_range(struct marker *begin,
struct marker *end)
{ }
#define GET_MARKER(name)
#endif /* CONFIG_MARKERS */
/**
* trace_mark - Marker using code patching
* @name: marker name, not quoted.
* @format: format string
* @args...: variable argument list
*
* Places a marker using optimized code patching technique (imv_read())
* to be enabled when immediate values are present.
*/
#define trace_mark(name, format, args...) \
__trace_mark(0, name, NULL, format, ## args)
/**
* _trace_mark - Marker using variable read
* @name: marker name, not quoted.
* @format: format string
* @args...: variable argument list
*
* Places a marker using a standard memory read (_imv_read()) to be
* enabled. Should be used for markers in code paths where instruction
* modification based enabling is not welcome. (__init and __exit functions,
* lockdep, some traps, printk).
*/
#define _trace_mark(name, format, args...) \
__trace_mark(1, name, NULL, format, ## args)
/**
* trace_mark_tp - Marker in a tracepoint callback
* @name: marker name, not quoted.
* @tp_name: tracepoint name, not quoted.
* @tp_cb: tracepoint callback. Should have an associated global symbol so it
* is not optimized away by the compiler (should not be static).
* @format: format string
* @args...: variable argument list
*
* Places a marker in a tracepoint callback.
*/
#define trace_mark_tp(name, tp_name, tp_cb, format, args...) \
__trace_mark_tp(name, NULL, tp_name, tp_cb, format, ## args)
/**
* MARK_NOARGS - Format string for a marker with no argument.
*/
#define MARK_NOARGS " "
/* To be used for string format validity checking with gcc */
static inline void __printf(1, 2) ___mark_check_format(const char *fmt, ...)
{
}
#define __mark_check_format(format, args...) \
do { \
if (0) \
___mark_check_format(format, ## args); \
} while (0)
extern marker_probe_func __mark_empty_function;
extern void marker_probe_cb(const struct marker *mdata,
void *call_private, ...);
/*
* Connect a probe to a marker.
* private data pointer must be a valid allocated memory address, or NULL.
*/
extern int marker_probe_register(const char *name, const char *format,
marker_probe_func *probe, void *probe_private);
/*
* Returns the private data given to marker_probe_register.
*/
extern int marker_probe_unregister(const char *name,
marker_probe_func *probe, void *probe_private);
/*
* Unregister a marker by providing the registered private data.
*/
extern int marker_probe_unregister_private_data(marker_probe_func *probe,
void *probe_private);
extern void *marker_get_private_data(const char *name, marker_probe_func *probe,
int num);
/*
* marker_synchronize_unregister must be called between the last marker probe
* unregistration and the first one of
* - the end of module exit function
* - the free of any resource used by the probes
* to ensure the code and data are valid for any possibly running probes.
*/
#define marker_synchronize_unregister() synchronize_sched()
#endif
......@@ -15,7 +15,6 @@
#include <linux/stringify.h>
#include <linux/kobject.h>
#include <linux/moduleparam.h>
#include <linux/marker.h>
#include <linux/tracepoint.h>
#include <asm/local.h>
......@@ -327,10 +326,6 @@ struct module
/* The command line arguments (may be mangled). People like
keeping pointers to this stuff */
char *args;
#ifdef CONFIG_MARKERS
struct marker *markers;
unsigned int num_markers;
#endif
#ifdef CONFIG_TRACEPOINTS
struct tracepoint *tracepoints;
unsigned int num_tracepoints;
......@@ -535,8 +530,6 @@ int unregister_module_notifier(struct notifier_block * nb);
extern void print_modules(void);
extern void module_update_markers(void);
extern void module_update_tracepoints(void);
extern int module_get_iter_tracepoints(struct tracepoint_iter *iter);
......@@ -651,10 +644,6 @@ static inline void print_modules(void)
{
}
static inline void module_update_markers(void)
{
}
static inline void module_update_tracepoints(void)
{
}
......
......@@ -1054,13 +1054,6 @@ config PROFILING
config TRACEPOINTS
bool
config MARKERS
bool "Activate markers"
select TRACEPOINTS
help
Place an empty function call at each marker site. Can be
dynamically changed for a probe function.
source "arch/Kconfig"
config SLOW_WORK
......
......@@ -87,7 +87,6 @@ obj-$(CONFIG_RELAY) += relay.o
obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o
obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o
obj-$(CONFIG_MARKERS) += marker.o
obj-$(CONFIG_TRACEPOINTS) += tracepoint.o
obj-$(CONFIG_LATENCYTOP) += latencytop.o
obj-$(CONFIG_FUNCTION_TRACER) += trace/
......
/*
* Copyright (C) 2007 Mathieu Desnoyers
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/types.h>
#include <linux/jhash.h>
#include <linux/list.h>
#include <linux/rcupdate.h>
#include <linux/marker.h>
#include <linux/err.h>
#include <linux/slab.h>
extern struct marker __start___markers[];
extern struct marker __stop___markers[];
/* Set to 1 to enable marker debug output */
static const int marker_debug;
/*
* markers_mutex nests inside module_mutex. Markers mutex protects the builtin
* and module markers and the hash table.
*/
static DEFINE_MUTEX(markers_mutex);
/*
* Marker hash table, containing the active markers.
* Protected by module_mutex.
*/
#define MARKER_HASH_BITS 6
#define MARKER_TABLE_SIZE (1 << MARKER_HASH_BITS)
static struct hlist_head marker_table[MARKER_TABLE_SIZE];
/*
* Note about RCU :
* It is used to make sure every handler has finished using its private data
* between two consecutive operation (add or remove) on a given marker. It is
* also used to delay the free of multiple probes array until a quiescent state
* is reached.
* marker entries modifications are protected by the markers_mutex.
*/
struct marker_entry {
struct hlist_node hlist;
char *format;
/* Probe wrapper */
void (*call)(const struct marker *mdata, void *call_private, ...);
struct marker_probe_closure single;
struct marker_probe_closure *multi;
int refcount; /* Number of times armed. 0 if disarmed. */
struct rcu_head rcu;
void *oldptr;
int rcu_pending;
unsigned char ptype:1;
unsigned char format_allocated:1;
char name[0]; /* Contains name'\0'format'\0' */
};
/**
* __mark_empty_function - Empty probe callback
* @probe_private: probe private data
* @call_private: call site private data
* @fmt: format string
* @...: variable argument list
*
* Empty callback provided as a probe to the markers. By providing this to a
* disabled marker, we make sure the execution flow is always valid even
* though the function pointer change and the marker enabling are two distinct
* operations that modifies the execution flow of preemptible code.
*/
notrace void __mark_empty_function(void *probe_private, void *call_private,
const char *fmt, va_list *args)
{
}
EXPORT_SYMBOL_GPL(__mark_empty_function);
/*
* marker_probe_cb Callback that prepares the variable argument list for probes.
* @mdata: pointer of type struct marker
* @call_private: caller site private data
* @...: Variable argument list.
*
* Since we do not use "typical" pointer based RCU in the 1 argument case, we
* need to put a full smp_rmb() in this branch. This is why we do not use
* rcu_dereference() for the pointer read.
*/
notrace void marker_probe_cb(const struct marker *mdata,
void *call_private, ...)
{
va_list args;
char ptype;
/*
* rcu_read_lock_sched does two things : disabling preemption to make
* sure the teardown of the callbacks can be done correctly when they
* are in modules and they insure RCU read coherency.
*/
rcu_read_lock_sched_notrace();
ptype = mdata->ptype;
if (likely(!ptype)) {
marker_probe_func *func;
/* Must read the ptype before ptr. They are not data dependant,
* so we put an explicit smp_rmb() here. */
smp_rmb();
func = mdata->single.func;
/* Must read the ptr before private data. They are not data
* dependant, so we put an explicit smp_rmb() here. */
smp_rmb();
va_start(args, call_private);
func(mdata->single.probe_private, call_private, mdata->format,
&args);
va_end(args);
} else {
struct marker_probe_closure *multi;
int i;
/*
* Read mdata->ptype before mdata->multi.
*/
smp_rmb();
multi = mdata->multi;
/*
* multi points to an array, therefore accessing the array
* depends on reading multi. However, even in this case,
* we must insure that the pointer is read _before_ the array
* data. Same as rcu_dereference, but we need a full smp_rmb()
* in the fast path, so put the explicit barrier here.
*/
smp_read_barrier_depends();
for (i = 0; multi[i].func; i++) {
va_start(args, call_private);
multi[i].func(multi[i].probe_private, call_private,
mdata->format, &args);
va_end(args);
}
}
rcu_read_unlock_sched_notrace();
}
EXPORT_SYMBOL_GPL(marker_probe_cb);
/*
* marker_probe_cb Callback that does not prepare the variable argument list.
* @mdata: pointer of type struct marker
* @call_private: caller site private data
* @...: Variable argument list.
*
* Should be connected to markers "MARK_NOARGS".
*/
static notrace void marker_probe_cb_noarg(const struct marker *mdata,
void *call_private, ...)
{
va_list args; /* not initialized */
char ptype;
rcu_read_lock_sched_notrace();
ptype = mdata->ptype;
if (likely(!ptype)) {
marker_probe_func *func;
/* Must read the ptype before ptr. They are not data dependant,
* so we put an explicit smp_rmb() here. */
smp_rmb();
func = mdata->single.func;
/* Must read the ptr before private data. They are not data
* dependant, so we put an explicit smp_rmb() here. */
smp_rmb();
func(mdata->single.probe_private, call_private, mdata->format,
&args);
} else {
struct marker_probe_closure *multi;
int i;
/*
* Read mdata->ptype before mdata->multi.
*/
smp_rmb();
multi = mdata->multi;
/*
* multi points to an array, therefore accessing the array
* depends on reading multi. However, even in this case,
* we must insure that the pointer is read _before_ the array
* data. Same as rcu_dereference, but we need a full smp_rmb()
* in the fast path, so put the explicit barrier here.
*/
smp_read_barrier_depends();
for (i = 0; multi[i].func; i++)
multi[i].func(multi[i].probe_private, call_private,
mdata->format, &args);
}
rcu_read_unlock_sched_notrace();
}
static void free_old_closure(struct rcu_head *head)
{
struct marker_entry *entry = container_of(head,
struct marker_entry, rcu);
kfree(entry->oldptr);
/* Make sure we free the data before setting the pending flag to 0 */
smp_wmb();
entry->rcu_pending = 0;
}
static void debug_print_probes(struct marker_entry *entry)
{
int i;
if (!marker_debug)
return;
if (!entry->ptype) {
printk(KERN_DEBUG "Single probe : %p %p\n",
entry->single.func,
entry->single.probe_private);
} else {
for (i = 0; entry->multi[i].func; i++)
printk(KERN_DEBUG "Multi probe %d : %p %p\n", i,
entry->multi[i].func,
entry->multi[i].probe_private);
}
}
static struct marker_probe_closure *
marker_entry_add_probe(struct marker_entry *entry,
marker_probe_func *probe, void *probe_private)
{
int nr_probes = 0;
struct marker_probe_closure *old, *new;
WARN_ON(!probe);
debug_print_probes(entry);
old = entry->multi;
if (!entry->ptype) {
if (entry->single.func == probe &&
entry->single.probe_private == probe_private)
return ERR_PTR(-EBUSY);
if (entry->single.func == __mark_empty_function) {
/* 0 -> 1 probes */
entry->single.func = probe;
entry->single.probe_private = probe_private;
entry->refcount = 1;
entry->ptype = 0;
debug_print_probes(entry);
return NULL;
} else {
/* 1 -> 2 probes */
nr_probes = 1;
old = NULL;
}
} else {
/* (N -> N+1), (N != 0, 1) probes */
for (nr_probes = 0; old[nr_probes].func; nr_probes++)
if (old[nr_probes].func == probe
&& old[nr_probes].probe_private
== probe_private)
return ERR_PTR(-EBUSY);
}
/* + 2 : one for new probe, one for NULL func */
new = kzalloc((nr_probes + 2) * sizeof(struct marker_probe_closure),
GFP_KERNEL);
if (new == NULL)
return ERR_PTR(-ENOMEM);
if (!old)
new[0] = entry->single;
else
memcpy(new, old,
nr_probes * sizeof(struct marker_probe_closure));
new[nr_probes].func = probe;
new[nr_probes].probe_private = probe_private;
entry->refcount = nr_probes + 1;
entry->multi = new;
entry->ptype = 1;
debug_print_probes(entry);
return old;
}
static struct marker_probe_closure *
marker_entry_remove_probe(struct marker_entry *entry,
marker_probe_func *probe, void *probe_private)
{
int nr_probes = 0, nr_del = 0, i;
struct marker_probe_closure *old, *new;
old = entry->multi;
debug_print_probes(entry);
if (!entry->ptype) {
/* 0 -> N is an error */
WARN_ON(entry->single.func == __mark_empty_function);
/* 1 -> 0 probes */
WARN_ON(probe && entry->single.func != probe);
WARN_ON(entry->single.probe_private != probe_private);
entry->single.func = __mark_empty_function;
entry->refcount = 0;
entry->ptype = 0;
debug_print_probes(entry);
return NULL;
} else {
/* (N -> M), (N > 1, M >= 0) probes */
for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
if ((!probe || old[nr_probes].func == probe)
&& old[nr_probes].probe_private
== probe_private)
nr_del++;
}
}
if (nr_probes - nr_del == 0) {
/* N -> 0, (N > 1) */
entry->single.func = __mark_empty_function;
entry->refcount = 0;
entry->ptype = 0;
} else if (nr_probes - nr_del == 1) {
/* N -> 1, (N > 1) */
for (i = 0; old[i].func; i++)
if ((probe && old[i].func != probe) ||
old[i].probe_private != probe_private)
entry->single = old[i];
entry->refcount = 1;
entry->ptype = 0;
} else {
int j = 0;
/* N -> M, (N > 1, M > 1) */
/* + 1 for NULL */
new = kzalloc((nr_probes - nr_del + 1)
* sizeof(struct marker_probe_closure), GFP_KERNEL);
if (new == NULL)
return ERR_PTR(-ENOMEM);
for (i = 0; old[i].func; i++)
if ((probe && old[i].func != probe) ||
old[i].probe_private != probe_private)
new[j++] = old[i];