[PATCH 00/11] [GIT PULL] tracing: Various tracing fixes and enhancements

[PATCH 00/11] [GIT PULL] tracing: Various tracing fixes and enhancements

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 2116 bytes --]


Ingo,

Please pull the latest tip/perf/core tree, which can be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/perf/core

Head SHA1: d840f718d28715a9833c1a8f46c2493ff3fd219b


Hiraku Toyooka (3):
      tracing: Replace static old_tracer check of tracer name
      tracing: Make a snapshot feature available from userspace
      tracing: Add documentation of snapshot utility

Josh Triplett (1):
      tracing: Mark tracing_dentry_percpu() static

Jovi Zhang (1):
      tracing: Remove second iterator initializer

Namhyung Kim (1):
      tracing: Use sched_clock_cpu for trace_clock_global

Shan Wei (1):
      tracing: Use __this_cpu_inc/dec operation instead of __get_cpu_var

Steven Rostedt (1):
      tracing: Remove tracepoint sample code

Steven Rostedt (Red Hat) (3):
      tracing/fgraph: Adjust fgraph depth before calling trace return callback
      ring-buffer: Add stats field for amount read from trace ring buffer
      tracing: Init current_trace to nop_trace and remove NULL checks

----
 Documentation/trace/ftrace.txt                 |   83 +++++++++
 include/linux/ftrace_event.h                   |    3 +
 include/linux/ring_buffer.h                    |    1 +
 kernel/trace/Kconfig                           |   10 ++
 kernel/trace/ring_buffer.c                     |   18 ++
 kernel/trace/trace.c                           |  222 +++++++++++++++++-------
 kernel/trace/trace.h                           |    1 +
 kernel/trace/trace_clock.c                     |    2 +-
 kernel/trace/trace_functions_graph.c           |    8 +-
 samples/Kconfig                                |    6 -
 samples/Makefile                               |    2 +-
 samples/tracepoints/Makefile                   |    6 -
 samples/tracepoints/tp-samples-trace.h         |   11 --
 samples/tracepoints/tracepoint-probe-sample.c  |   57 ------
 samples/tracepoints/tracepoint-probe-sample2.c |   44 -----
 samples/tracepoints/tracepoint-sample.c        |   57 ------
 16 files changed, 288 insertions(+), 243 deletions(-)

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 01/11] tracing: Mark tracing_dentry_percpu() static

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 828 bytes --]

From: Josh Triplett <josh@joshtriplett.org>

Nothing outside of kernel/trace/trace.c references tracing_dentry_percpu().

Link: http://lkml.kernel.org/r/1353302917-13995-7-git-send-email-josh@joshtriplett.org

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d2a6583..ca9b7df 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4506,7 +4506,7 @@ struct dentry *tracing_init_dentry(void)
 
 static struct dentry *d_percpu;
 
-struct dentry *tracing_dentry_percpu(void)
+static struct dentry *tracing_dentry_percpu(void)
 {
 	static int once;
 	struct dentry *d_tracer;
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 02/11] tracing: Remove tracepoint sample code

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 8104 bytes --]

From: Steven Rostedt <srostedt@redhat.com>

The tracepoint sample code was used to teach developers how to
create their own tracepoints. But now the trace_events have been
added as a higher level that is used directly by developers today.

Only the trace_event code should use the tracepoint interface
directly and no new tracepoints should be added.

Besides, the example had a race condition with the use of the
 ->d_name.name dentry field, as pointed out by Al Viro.

Best just to remove the code so it wont be used by other developers.

Link: http://lkml.kernel.org/r/20130123225523.GY4939@ZenIV.linux.org.uk

Cc: Al Viro <viro@ZenIV.linux.org.uk>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 samples/Kconfig                                |    6 ---
 samples/Makefile                               |    2 +-
 samples/tracepoints/Makefile                   |    6 ---
 samples/tracepoints/tp-samples-trace.h         |   11 -----
 samples/tracepoints/tracepoint-probe-sample.c  |   57 ------------------------
 samples/tracepoints/tracepoint-probe-sample2.c |   44 ------------------
 samples/tracepoints/tracepoint-sample.c        |   57 ------------------------
 7 files changed, 1 insertion(+), 182 deletions(-)
 delete mode 100644 samples/tracepoints/Makefile
 delete mode 100644 samples/tracepoints/tp-samples-trace.h
 delete mode 100644 samples/tracepoints/tracepoint-probe-sample.c
 delete mode 100644 samples/tracepoints/tracepoint-probe-sample2.c
 delete mode 100644 samples/tracepoints/tracepoint-sample.c

diff --git a/samples/Kconfig b/samples/Kconfig
index 7b6792a..6181c2c 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -5,12 +5,6 @@ menuconfig SAMPLES
 
 if SAMPLES
 
-config SAMPLE_TRACEPOINTS
-	tristate "Build tracepoints examples -- loadable modules only"
-	depends on TRACEPOINTS && m
-	help
-	  This build tracepoints example modules.
-
 config SAMPLE_TRACE_EVENTS
 	tristate "Build trace_events examples -- loadable modules only"
 	depends on EVENT_TRACING && m
diff --git a/samples/Makefile b/samples/Makefile
index 5ef08bb..1a60c62 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -1,4 +1,4 @@
 # Makefile for Linux samples code
 
-obj-$(CONFIG_SAMPLES)	+= kobject/ kprobes/ tracepoints/ trace_events/ \
+obj-$(CONFIG_SAMPLES)	+= kobject/ kprobes/ trace_events/ \
 			   hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/
diff --git a/samples/tracepoints/Makefile b/samples/tracepoints/Makefile
deleted file mode 100644
index 36479ad..0000000
--- a/samples/tracepoints/Makefile
+++ /dev/null
@@ -1,6 +0,0 @@
-# builds the tracepoint example kernel modules;
-# then to use one (as root):  insmod <module_name.ko>
-
-obj-$(CONFIG_SAMPLE_TRACEPOINTS) += tracepoint-sample.o
-obj-$(CONFIG_SAMPLE_TRACEPOINTS) += tracepoint-probe-sample.o
-obj-$(CONFIG_SAMPLE_TRACEPOINTS) += tracepoint-probe-sample2.o
diff --git a/samples/tracepoints/tp-samples-trace.h b/samples/tracepoints/tp-samples-trace.h
deleted file mode 100644
index 4d46be9..0000000
--- a/samples/tracepoints/tp-samples-trace.h
+++ /dev/null
@@ -1,11 +0,0 @@
-#ifndef _TP_SAMPLES_TRACE_H
-#define _TP_SAMPLES_TRACE_H
-
-#include <linux/proc_fs.h>	/* for struct inode and struct file */
-#include <linux/tracepoint.h>
-
-DECLARE_TRACE(subsys_event,
-	TP_PROTO(struct inode *inode, struct file *file),
-	TP_ARGS(inode, file));
-DECLARE_TRACE_NOARGS(subsys_eventb);
-#endif
diff --git a/samples/tracepoints/tracepoint-probe-sample.c b/samples/tracepoints/tracepoint-probe-sample.c
deleted file mode 100644
index 744c0b9..0000000
--- a/samples/tracepoints/tracepoint-probe-sample.c
+++ /dev/null
@@ -1,57 +0,0 @@
-/*
- * tracepoint-probe-sample.c
- *
- * sample tracepoint probes.
- */
-
-#include <linux/module.h>
-#include <linux/file.h>
-#include <linux/dcache.h>
-#include "tp-samples-trace.h"
-
-/*
- * Here the caller only guarantees locking for struct file and struct inode.
- * Locking must therefore be done in the probe to use the dentry.
- */
-static void probe_subsys_event(void *ignore,
-			       struct inode *inode, struct file *file)
-{
-	path_get(&file->f_path);
-	dget(file->f_path.dentry);
-	printk(KERN_INFO "Event is encountered with filename %s\n",
-		file->f_path.dentry->d_name.name);
-	dput(file->f_path.dentry);
-	path_put(&file->f_path);
-}
-
-static void probe_subsys_eventb(void *ignore)
-{
-	printk(KERN_INFO "Event B is encountered\n");
-}
-
-static int __init tp_sample_trace_init(void)
-{
-	int ret;
-
-	ret = register_trace_subsys_event(probe_subsys_event, NULL);
-	WARN_ON(ret);
-	ret = register_trace_subsys_eventb(probe_subsys_eventb, NULL);
-	WARN_ON(ret);
-
-	return 0;
-}
-
-module_init(tp_sample_trace_init);
-
-static void __exit tp_sample_trace_exit(void)
-{
-	unregister_trace_subsys_eventb(probe_subsys_eventb, NULL);
-	unregister_trace_subsys_event(probe_subsys_event, NULL);
-	tracepoint_synchronize_unregister();
-}
-
-module_exit(tp_sample_trace_exit);
-
-MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Mathieu Desnoyers");
-MODULE_DESCRIPTION("Tracepoint Probes Samples");
diff --git a/samples/tracepoints/tracepoint-probe-sample2.c b/samples/tracepoints/tracepoint-probe-sample2.c
deleted file mode 100644
index 9fcf990..0000000
--- a/samples/tracepoints/tracepoint-probe-sample2.c
+++ /dev/null
@@ -1,44 +0,0 @@
-/*
- * tracepoint-probe-sample2.c
- *
- * 2nd sample tracepoint probes.
- */
-
-#include <linux/module.h>
-#include <linux/fs.h>
-#include "tp-samples-trace.h"
-
-/*
- * Here the caller only guarantees locking for struct file and struct inode.
- * Locking must therefore be done in the probe to use the dentry.
- */
-static void probe_subsys_event(void *ignore,
-			       struct inode *inode, struct file *file)
-{
-	printk(KERN_INFO "Event is encountered with inode number %lu\n",
-		inode->i_ino);
-}
-
-static int __init tp_sample_trace_init(void)
-{
-	int ret;
-
-	ret = register_trace_subsys_event(probe_subsys_event, NULL);
-	WARN_ON(ret);
-
-	return 0;
-}
-
-module_init(tp_sample_trace_init);
-
-static void __exit tp_sample_trace_exit(void)
-{
-	unregister_trace_subsys_event(probe_subsys_event, NULL);
-	tracepoint_synchronize_unregister();
-}
-
-module_exit(tp_sample_trace_exit);
-
-MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Mathieu Desnoyers");
-MODULE_DESCRIPTION("Tracepoint Probes Samples");
diff --git a/samples/tracepoints/tracepoint-sample.c b/samples/tracepoints/tracepoint-sample.c
deleted file mode 100644
index f4d89e0..0000000
--- a/samples/tracepoints/tracepoint-sample.c
+++ /dev/null
@@ -1,57 +0,0 @@
-/* tracepoint-sample.c
- *
- * Executes a tracepoint when /proc/tracepoint-sample is opened.
- *
- * (C) Copyright 2007 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
- *
- * This file is released under the GPLv2.
- * See the file COPYING for more details.
- */
-
-#include <linux/module.h>
-#include <linux/sched.h>
-#include <linux/proc_fs.h>
-#include "tp-samples-trace.h"
-
-DEFINE_TRACE(subsys_event);
-DEFINE_TRACE(subsys_eventb);
-
-struct proc_dir_entry *pentry_sample;
-
-static int my_open(struct inode *inode, struct file *file)
-{
-	int i;
-
-	trace_subsys_event(inode, file);
-	for (i = 0; i < 10; i++)
-		trace_subsys_eventb();
-	return -EPERM;
-}
-
-static const struct file_operations mark_ops = {
-	.open = my_open,
-	.llseek = noop_llseek,
-};
-
-static int __init sample_init(void)
-{
-	printk(KERN_ALERT "sample init\n");
-	pentry_sample = proc_create("tracepoint-sample", 0444, NULL,
-		&mark_ops);
-	if (!pentry_sample)
-		return -EPERM;
-	return 0;
-}
-
-static void __exit sample_exit(void)
-{
-	printk(KERN_ALERT "sample exit\n");
-	remove_proc_entry("tracepoint-sample", NULL);
-}
-
-module_init(sample_init)
-module_exit(sample_exit)
-
-MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Mathieu Desnoyers");
-MODULE_DESCRIPTION("Tracepoint sample");
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 03/11] tracing: Use __this_cpu_inc/dec operation instead of __get_cpu_var

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 1274 bytes --]

From: Shan Wei <davidshan@tencent.com>

__this_cpu_inc_return() or __this_cpu_dec generates a single instruction,
which is faster than __get_cpu_var operation.

Link: http://lkml.kernel.org/r/50A9C1BD.1060308@gmail.com

Reviewed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Shan Wei <davidshan@tencent.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ca9b7df..07888e1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1344,7 +1344,7 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
 	 */
 	preempt_disable_notrace();
 
-	use_stack = ++__get_cpu_var(ftrace_stack_reserve);
+	use_stack = __this_cpu_inc_return(ftrace_stack_reserve);
 	/*
 	 * We don't need any atomic variables, just a barrier.
 	 * If an interrupt comes in, we don't care, because it would
@@ -1398,7 +1398,7 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
  out:
 	/* Again, don't let gcc optimize things here */
 	barrier();
-	__get_cpu_var(ftrace_stack_reserve)--;
+	__this_cpu_dec(ftrace_stack_reserve);
 	preempt_enable_notrace();
 
 }
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 04/11] tracing: Remove second iterator initializer

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 1233 bytes --]

From: Jovi Zhang <bookjovi@gmail.com>

The trace iterator is already initialized by trace_init_global_iter(),
so there is no need to initialize it again.

Link: http://lkml.kernel.org/r/CACV3sb+G1YnO6168JhY3dEadmJi58pA5-2cSZT8E0WVHJNFt9Q@mail.gmail.com

Signed-off-by: Jovi Zhang <bookjovi@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 07888e1..d399592 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5030,6 +5030,7 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
 	if (disable_tracing)
 		ftrace_kill();
 
+	/* Simulate the iterator */
 	trace_init_global_iter(&iter);
 
 	for_each_tracing_cpu(cpu) {
@@ -5041,10 +5042,6 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
 	/* don't look at user memory in panic mode */
 	trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
 
-	/* Simulate the iterator */
-	iter.tr = &global_trace;
-	iter.trace = current_trace;
-
 	switch (oops_dump_mode) {
 	case DUMP_ALL:
 		iter.cpu_file = TRACE_PIPE_ALL_CPU;
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 05/11] tracing/fgraph: Adjust fgraph depth before calling trace return callback

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 2656 bytes --]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

While debugging the virtual cputime with the function graph tracer
with a max_depth of 1 (most common use of the max_depth so far),
I found that I was missing kernel execution because of a race condition.

The code for the return side of the function has a slight race:

	ftrace_pop_return_trace(&trace, &ret, frame_pointer);
	trace.rettime = trace_clock_local();
	ftrace_graph_return(&trace);
	barrier();
	current->curr_ret_stack--;

The ftrace_pop_return_trace() initializes the trace structure for
the callback. The ftrace_graph_return() uses the trace structure
for its own use as that structure is on the stack and is local
to this function. Then the curr_ret_stack is decremented which
is what the trace.depth is set to.

If an interrupt comes in after the ftrace_graph_return() but
before the curr_ret_stack, then the called function will get
a depth of 2. If max_depth is set to 1 this function will be
ignored.

The problem is that the trace has already been called, and the
timestamp for that trace will not reflect the time the function
was about to re-enter userspace. Calls to the interrupt will not
be traced because the max_depth has prevented this.

To solve this issue, the ftrace_graph_return() can safely be
moved after the current->curr_ret_stack has been updated.
This way the timestamp for the return callback will reflect
the actual time.

If an interrupt comes in after the curr_ret_stack update and
ftrace_graph_return(), it will be traced. It may look a little
confusing to see it within the other function, but at least
it will not be lost.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace_functions_graph.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 7008d2e..39ada66 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -191,10 +191,16 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
 
 	ftrace_pop_return_trace(&trace, &ret, frame_pointer);
 	trace.rettime = trace_clock_local();
-	ftrace_graph_return(&trace);
 	barrier();
 	current->curr_ret_stack--;
 
+	/*
+	 * The trace should run after decrementing the ret counter
+	 * in case an interrupt were to come in. We don't want to
+	 * lose the interrupt if max_depth is set.
+	 */
+	ftrace_graph_return(&trace);
+
 	if (unlikely(!ret)) {
 		ftrace_graph_stop();
 		WARN_ON(1);
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 06/11] ring-buffer: Add stats field for amount read from trace ring buffer

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 2797 bytes --]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

Add a stat about the number of events read from the ring buffer:

 #  cat /debug/tracing/per_cpu/cpu0/stats
entries: 39869
overrun: 870512
commit overrun: 0
bytes: 1449912
oldest event ts:  6561.368690
now ts:  6565.246426
dropped events: 0
read events: 112    <-- Added

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/ring_buffer.h |    1 +
 kernel/trace/ring_buffer.c  |   18 ++++++++++++++++++
 kernel/trace/trace.c        |    3 +++
 3 files changed, 22 insertions(+)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 519777e..1342e69 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -167,6 +167,7 @@ unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu);
 unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu);
 unsigned long ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu);
 unsigned long ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu);
+unsigned long ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu);
 
 u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu);
 void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 13950d9..7244acd 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3103,6 +3103,24 @@ ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
 EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
 
 /**
+ * ring_buffer_read_events_cpu - get the number of events successfully read
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to get the number of events read
+ */
+unsigned long
+ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	cpu_buffer = buffer->buffers[cpu];
+	return cpu_buffer->read;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
+
+/**
  * ring_buffer_entries - get the number of entries in a buffer
  * @buffer: The ring buffer
  *
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d399592..90a1c71 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4430,6 +4430,9 @@ tracing_stats_read(struct file *filp, char __user *ubuf,
 	cnt = ring_buffer_dropped_events_cpu(tr->buffer, cpu);
 	trace_seq_printf(s, "dropped events: %ld\n", cnt);
 
+	cnt = ring_buffer_read_events_cpu(tr->buffer, cpu);
+	trace_seq_printf(s, "read events: %ld\n", cnt);
+
 	count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len);
 
 	kfree(s);
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 07/11] tracing: Use sched_clock_cpu for trace_clock_global

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 1074 bytes --]

From: Namhyung Kim <namhyung.kim@lge.com>

For systems with an unstable sched_clock, all cpu_clock() does is enable/
disable local irq during the call to sched_clock_cpu().  And for stable
systems they are same.

trace_clock_global() already disables interrupts, so it can call
sched_clock_cpu() directly.

Link: http://lkml.kernel.org/r/1356576585-28782-2-git-send-email-namhyung@kernel.org

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace_clock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index 22b638b..24bf48e 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -84,7 +84,7 @@ u64 notrace trace_clock_global(void)
 	local_irq_save(flags);
 
 	this_cpu = raw_smp_processor_id();
-	now = cpu_clock(this_cpu);
+	now = sched_clock_cpu(this_cpu);
 	/*
 	 * If in an NMI context then dont risk lockups and return the
 	 * cpu_clock() time:
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 08/11] tracing: Replace static old_tracer check of tracer name

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 3559 bytes --]

From: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>

Currently the trace buffer read functions use a static variable
"old_tracer" for detecting if the current tracer changes. This
was suitable for a single trace file ("trace"), but to add a
snapshot feature that will use the same function for its file,
a check against a static variable is not sufficient.

To use the output functions for two different files, instead of
storing the current tracer in a static variable, as the trace
iterator descriptor contains a pointer to the original current
tracer's name, that pointer can now be used to check if the
current tracer has changed between different reads of the trace
file.

Link: http://lkml.kernel.org/r/20121226025252.3252.9276.stgit@liselsia

Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace.c |   22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 90a1c71..2c72466 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1948,18 +1948,20 @@ void tracing_iter_reset(struct trace_iterator *iter, int cpu)
 static void *s_start(struct seq_file *m, loff_t *pos)
 {
 	struct trace_iterator *iter = m->private;
-	static struct tracer *old_tracer;
 	int cpu_file = iter->cpu_file;
 	void *p = NULL;
 	loff_t l = 0;
 	int cpu;
 
-	/* copy the tracer to avoid using a global lock all around */
+	/*
+	 * copy the tracer to avoid using a global lock all around.
+	 * iter->trace is a copy of current_trace, the pointer to the
+	 * name may be used instead of a strcmp(), as iter->trace->name
+	 * will point to the same string as current_trace->name.
+	 */
 	mutex_lock(&trace_types_lock);
-	if (unlikely(old_tracer != current_trace && current_trace)) {
-		old_tracer = current_trace;
+	if (unlikely(current_trace && iter->trace->name != current_trace->name))
 		*iter->trace = *current_trace;
-	}
 	mutex_unlock(&trace_types_lock);
 
 	atomic_inc(&trace_record_cmdline_disabled);
@@ -3494,7 +3496,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 		  size_t cnt, loff_t *ppos)
 {
 	struct trace_iterator *iter = filp->private_data;
-	static struct tracer *old_tracer;
 	ssize_t sret;
 
 	/* return any leftover data */
@@ -3506,10 +3507,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 
 	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
-	if (unlikely(old_tracer != current_trace && current_trace)) {
-		old_tracer = current_trace;
+	if (unlikely(current_trace && iter->trace->name != current_trace->name))
 		*iter->trace = *current_trace;
-	}
 	mutex_unlock(&trace_types_lock);
 
 	/*
@@ -3665,7 +3664,6 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 		.ops		= &tracing_pipe_buf_ops,
 		.spd_release	= tracing_spd_release_pipe,
 	};
-	static struct tracer *old_tracer;
 	ssize_t ret;
 	size_t rem;
 	unsigned int i;
@@ -3675,10 +3673,8 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 
 	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
-	if (unlikely(old_tracer != current_trace && current_trace)) {
-		old_tracer = current_trace;
+	if (unlikely(current_trace && iter->trace->name != current_trace->name))
 		*iter->trace = *current_trace;
-	}
 	mutex_unlock(&trace_types_lock);
 
 	mutex_lock(&iter->mutex);
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 09/11] tracing: Make a snapshot feature available from userspace

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 11499 bytes --]

From: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>

Ftrace has a snapshot feature available from kernel space and
latency tracers (e.g. irqsoff) are using it. This patch enables
user applictions to take a snapshot via debugfs.

Add "snapshot" debugfs file in "tracing" directory.

  snapshot:
    This is used to take a snapshot and to read the output of the
    snapshot.

     # echo 1 > snapshot

    This will allocate the spare buffer for snapshot (if it is
    not allocated), and take a snapshot.

     # cat snapshot

    This will show contents of the snapshot.

     # echo 0 > snapshot

    This will free the snapshot if it is allocated.

    Any other positive values will clear the snapshot contents if
    the snapshot is allocated, or return EINVAL if it is not allocated.

Link: http://lkml.kernel.org/r/20121226025300.3252.86850.stgit@liselsia

Cc: Jiri Olsa <jolsa@redhat.com>
Cc: David Sharp <dhsharp@google.com>
Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
[
   Fixed irqsoff selftest and also a conflict with a change
   that fixes the update_max_tr.
]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/ftrace_event.h |    3 +
 kernel/trace/Kconfig         |   10 +++
 kernel/trace/trace.c         |  166 +++++++++++++++++++++++++++++++++++-------
 kernel/trace/trace.h         |    1 +
 4 files changed, 154 insertions(+), 26 deletions(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 6f8d0b7..13a54d0 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -83,6 +83,9 @@ struct trace_iterator {
 	long			idx;
 
 	cpumask_var_t		started;
+
+	/* it's true when current open file is snapshot */
+	bool			snapshot;
 };
 
 enum trace_iter_flags {
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index cdc9d28..3656756 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -253,6 +253,16 @@ config FTRACE_SYSCALLS
 	help
 	  Basic tracer to catch the syscall entry and exit events.
 
+config TRACER_SNAPSHOT
+	bool "Create a snapshot trace buffer"
+	select TRACER_MAX_TRACE
+	help
+	  Allow tracing users to take snapshot of the current buffer using the
+	  ftrace interface, e.g.:
+
+	      echo 1 > /sys/kernel/debug/tracing/snapshot
+	      cat snapshot
+
 config TRACE_BRANCH_PROFILING
 	bool
 	select GENERIC_TRACER
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2c72466..70dce64 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -710,12 +710,11 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 
 	WARN_ON_ONCE(!irqs_disabled());
 
-	/* If we disabled the tracer, stop now */
-	if (current_trace == &nop_trace)
-		return;
-
-	if (WARN_ON_ONCE(!current_trace->use_max_tr))
+	if (!current_trace->allocated_snapshot) {
+		/* Only the nop tracer should hit this when disabling */
+		WARN_ON_ONCE(current_trace != &nop_trace);
 		return;
+	}
 
 	arch_spin_lock(&ftrace_max_lock);
 
@@ -743,10 +742,8 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
 		return;
 
 	WARN_ON_ONCE(!irqs_disabled());
-	if (!current_trace->use_max_tr) {
-		WARN_ON_ONCE(1);
+	if (WARN_ON_ONCE(!current_trace->allocated_snapshot))
 		return;
-	}
 
 	arch_spin_lock(&ftrace_max_lock);
 
@@ -866,10 +863,13 @@ int register_tracer(struct tracer *type)
 
 		current_trace = type;
 
-		/* If we expanded the buffers, make sure the max is expanded too */
-		if (ring_buffer_expanded && type->use_max_tr)
-			ring_buffer_resize(max_tr.buffer, trace_buf_size,
-						RING_BUFFER_ALL_CPUS);
+		if (type->use_max_tr) {
+			/* If we expanded the buffers, make sure the max is expanded too */
+			if (ring_buffer_expanded)
+				ring_buffer_resize(max_tr.buffer, trace_buf_size,
+						   RING_BUFFER_ALL_CPUS);
+			type->allocated_snapshot = true;
+		}
 
 		/* the test is responsible for initializing and enabling */
 		pr_info("Testing tracer %s: ", type->name);
@@ -885,10 +885,14 @@ int register_tracer(struct tracer *type)
 		/* Only reset on passing, to avoid touching corrupted buffers */
 		tracing_reset_online_cpus(tr);
 
-		/* Shrink the max buffer again */
-		if (ring_buffer_expanded && type->use_max_tr)
-			ring_buffer_resize(max_tr.buffer, 1,
-						RING_BUFFER_ALL_CPUS);
+		if (type->use_max_tr) {
+			type->allocated_snapshot = false;
+
+			/* Shrink the max buffer again */
+			if (ring_buffer_expanded)
+				ring_buffer_resize(max_tr.buffer, 1,
+						   RING_BUFFER_ALL_CPUS);
+		}
 
 		printk(KERN_CONT "PASSED\n");
 	}
@@ -1964,7 +1968,11 @@ static void *s_start(struct seq_file *m, loff_t *pos)
 		*iter->trace = *current_trace;
 	mutex_unlock(&trace_types_lock);
 
-	atomic_inc(&trace_record_cmdline_disabled);
+	if (iter->snapshot && iter->trace->use_max_tr)
+		return ERR_PTR(-EBUSY);
+
+	if (!iter->snapshot)
+		atomic_inc(&trace_record_cmdline_disabled);
 
 	if (*pos != iter->pos) {
 		iter->ent = NULL;
@@ -2003,7 +2011,11 @@ static void s_stop(struct seq_file *m, void *p)
 {
 	struct trace_iterator *iter = m->private;
 
-	atomic_dec(&trace_record_cmdline_disabled);
+	if (iter->snapshot && iter->trace->use_max_tr)
+		return;
+
+	if (!iter->snapshot)
+		atomic_dec(&trace_record_cmdline_disabled);
 	trace_access_unlock(iter->cpu_file);
 	trace_event_read_unlock();
 }
@@ -2438,7 +2450,7 @@ static const struct seq_operations tracer_seq_ops = {
 };
 
 static struct trace_iterator *
-__tracing_open(struct inode *inode, struct file *file)
+__tracing_open(struct inode *inode, struct file *file, bool snapshot)
 {
 	long cpu_file = (long) inode->i_private;
 	struct trace_iterator *iter;
@@ -2471,10 +2483,11 @@ __tracing_open(struct inode *inode, struct file *file)
 	if (!zalloc_cpumask_var(&iter->started, GFP_KERNEL))
 		goto fail;
 
-	if (current_trace && current_trace->print_max)
+	if ((current_trace && current_trace->print_max) || snapshot)
 		iter->tr = &max_tr;
 	else
 		iter->tr = &global_trace;
+	iter->snapshot = snapshot;
 	iter->pos = -1;
 	mutex_init(&iter->mutex);
 	iter->cpu_file = cpu_file;
@@ -2491,8 +2504,9 @@ __tracing_open(struct inode *inode, struct file *file)
 	if (trace_clocks[trace_clock_id].in_ns)
 		iter->iter_flags |= TRACE_FILE_TIME_IN_NS;
 
-	/* stop the trace while dumping */
-	tracing_stop();
+	/* stop the trace while dumping if we are not opening "snapshot" */
+	if (!iter->snapshot)
+		tracing_stop();
 
 	if (iter->cpu_file == TRACE_PIPE_ALL_CPU) {
 		for_each_tracing_cpu(cpu) {
@@ -2555,8 +2569,9 @@ static int tracing_release(struct inode *inode, struct file *file)
 	if (iter->trace && iter->trace->close)
 		iter->trace->close(iter);
 
-	/* reenable tracing if it was previously enabled */
-	tracing_start();
+	if (!iter->snapshot)
+		/* reenable tracing if it was previously enabled */
+		tracing_start();
 	mutex_unlock(&trace_types_lock);
 
 	mutex_destroy(&iter->mutex);
@@ -2584,7 +2599,7 @@ static int tracing_open(struct inode *inode, struct file *file)
 	}
 
 	if (file->f_mode & FMODE_READ) {
-		iter = __tracing_open(inode, file);
+		iter = __tracing_open(inode, file, false);
 		if (IS_ERR(iter))
 			ret = PTR_ERR(iter);
 		else if (trace_flags & TRACE_ITER_LATENCY_FMT)
@@ -3219,7 +3234,7 @@ static int tracing_set_tracer(const char *buf)
 	if (current_trace && current_trace->reset)
 		current_trace->reset(tr);
 
-	had_max_tr = current_trace && current_trace->use_max_tr;
+	had_max_tr = current_trace && current_trace->allocated_snapshot;
 	current_trace = &nop_trace;
 
 	if (had_max_tr && !t->use_max_tr) {
@@ -3238,6 +3253,8 @@ static int tracing_set_tracer(const char *buf)
 		 */
 		ring_buffer_resize(max_tr.buffer, 1, RING_BUFFER_ALL_CPUS);
 		set_buffer_entries(&max_tr, 1);
+		tracing_reset_online_cpus(&max_tr);
+		current_trace->allocated_snapshot = false;
 	}
 	destroy_trace_option_files(topts);
 
@@ -3248,6 +3265,7 @@ static int tracing_set_tracer(const char *buf)
 						   RING_BUFFER_ALL_CPUS);
 		if (ret < 0)
 			goto out;
+		t->allocated_snapshot = true;
 	}
 
 	if (t->init) {
@@ -4066,6 +4084,87 @@ static int tracing_clock_open(struct inode *inode, struct file *file)
 	return single_open(file, tracing_clock_show, NULL);
 }
 
+#ifdef CONFIG_TRACER_SNAPSHOT
+static int tracing_snapshot_open(struct inode *inode, struct file *file)
+{
+	struct trace_iterator *iter;
+	int ret = 0;
+
+	if (file->f_mode & FMODE_READ) {
+		iter = __tracing_open(inode, file, true);
+		if (IS_ERR(iter))
+			ret = PTR_ERR(iter);
+	}
+	return ret;
+}
+
+static ssize_t
+tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
+		       loff_t *ppos)
+{
+	unsigned long val;
+	int ret;
+
+	ret = tracing_update_buffers();
+	if (ret < 0)
+		return ret;
+
+	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+	if (ret)
+		return ret;
+
+	mutex_lock(&trace_types_lock);
+
+	if (current_trace && current_trace->use_max_tr) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	switch (val) {
+	case 0:
+		if (current_trace->allocated_snapshot) {
+			/* free spare buffer */
+			ring_buffer_resize(max_tr.buffer, 1,
+					   RING_BUFFER_ALL_CPUS);
+			set_buffer_entries(&max_tr, 1);
+			tracing_reset_online_cpus(&max_tr);
+			current_trace->allocated_snapshot = false;
+		}
+		break;
+	case 1:
+		if (!current_trace->allocated_snapshot) {
+			/* allocate spare buffer */
+			ret = resize_buffer_duplicate_size(&max_tr,
+					&global_trace, RING_BUFFER_ALL_CPUS);
+			if (ret < 0)
+				break;
+			current_trace->allocated_snapshot = true;
+		}
+
+		local_irq_disable();
+		/* Now, we're going to swap */
+		update_max_tr(&global_trace, current, smp_processor_id());
+		local_irq_enable();
+		break;
+	default:
+		if (current_trace->allocated_snapshot)
+			tracing_reset_online_cpus(&max_tr);
+		else
+			ret = -EINVAL;
+		break;
+	}
+
+	if (ret >= 0) {
+		*ppos += cnt;
+		ret = cnt;
+	}
+out:
+	mutex_unlock(&trace_types_lock);
+	return ret;
+}
+#endif /* CONFIG_TRACER_SNAPSHOT */
+
+
 static const struct file_operations tracing_max_lat_fops = {
 	.open		= tracing_open_generic,
 	.read		= tracing_max_lat_read,
@@ -4122,6 +4221,16 @@ static const struct file_operations trace_clock_fops = {
 	.write		= tracing_clock_write,
 };
 
+#ifdef CONFIG_TRACER_SNAPSHOT
+static const struct file_operations snapshot_fops = {
+	.open		= tracing_snapshot_open,
+	.read		= seq_read,
+	.write		= tracing_snapshot_write,
+	.llseek		= tracing_seek,
+	.release	= tracing_release,
+};
+#endif /* CONFIG_TRACER_SNAPSHOT */
+
 struct ftrace_buffer_info {
 	struct trace_array	*tr;
 	void			*spare;
@@ -4921,6 +5030,11 @@ static __init int tracer_init_debugfs(void)
 			&ftrace_update_tot_cnt, &tracing_dyn_info_fops);
 #endif
 
+#ifdef CONFIG_TRACER_SNAPSHOT
+	trace_create_file("snapshot", 0644, d_tracer,
+			  (void *) TRACE_PIPE_ALL_CPU, &snapshot_fops);
+#endif
+
 	create_trace_options_dir();
 
 	for_each_tracing_cpu(cpu)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 04a2c7a..57d7e53 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -287,6 +287,7 @@ struct tracer {
 	struct tracer_flags	*flags;
 	bool			print_max;
 	bool			use_max_tr;
+	bool			allocated_snapshot;
 };
 
 
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 10/11] tracing: Add documentation of snapshot utility

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 4661 bytes --]

From: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>

This patch adds snapshot description in ftrace documentation.
This description includes what the snapshot is and how to use it.

Link: http://lkml.kernel.org/r/20121226025309.3252.150.stgit@liselsia

Cc: Rob Landley <rob@landley.net>
Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 Documentation/trace/ftrace.txt |   83 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 6f51fed..53d6a3c 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -1842,6 +1842,89 @@ an error.
  # cat buffer_size_kb
 85
 
+Snapshot
+--------
+CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature
+available to all non latency tracers. (Latency tracers which
+record max latency, such as "irqsoff" or "wakeup", can't use
+this feature, since those are already using the snapshot
+mechanism internally.)
+
+Snapshot preserves a current trace buffer at a particular point
+in time without stopping tracing. Ftrace swaps the current
+buffer with a spare buffer, and tracing continues in the new
+current (=previous spare) buffer.
+
+The following debugfs files in "tracing" are related to this
+feature:
+
+  snapshot:
+
+	This is used to take a snapshot and to read the output
+	of the snapshot. Echo 1 into this file to allocate a
+	spare buffer and to take a snapshot (swap), then read
+	the snapshot from this file in the same format as
+	"trace" (described above in the section "The File
+	System"). Both reads snapshot and tracing are executable
+	in parallel. When the spare buffer is allocated, echoing
+	0 frees it, and echoing else (positive) values clear the
+	snapshot contents.
+	More details are shown in the table below.
+
+	status\input  |     0      |     1      |    else    |
+	--------------+------------+------------+------------+
+	not allocated |(do nothing)| alloc+swap |   EINVAL   |
+	--------------+------------+------------+------------+
+	allocated     |    free    |    swap    |   clear    |
+	--------------+------------+------------+------------+
+
+Here is an example of using the snapshot feature.
+
+ # echo 1 > events/sched/enable
+ # echo 1 > snapshot
+ # cat snapshot
+# tracer: nop
+#
+# entries-in-buffer/entries-written: 71/71   #P:8
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+          <idle>-0     [005] d...  2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120
+           sleep-2242  [005] d...  2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120
+[...]
+          <idle>-0     [002] d...  2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120
+
+ # cat trace
+# tracer: nop
+#
+# entries-in-buffer/entries-written: 77/77   #P:8
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+          <idle>-0     [007] d...  2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120
+ snapshot-test-2-2229  [002] d...  2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120
+[...]
+
+
+If you try to use this snapshot feature when current tracer is
+one of the latency tracers, you will get the following results.
+
+ # echo wakeup > current_tracer
+ # echo 1 > snapshot
+bash: echo: write error: Device or resource busy
+ # cat snapshot
+cat: snapshot: Device or resource busy
+
 -----------
 
 More details can be found in the source code, in the
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

[PATCH 11/11] tracing: Init current_trace to nop_trace and remove NULL checks

[Steven Rostedt]

[-- Attachment #1: Type: text/plain, Size: 4832 bytes --]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

On early boot up, when the ftrace ring buffer is initialized, the
static variable current_trace is initialized to &nop_trace.
Before this initialization, current_trace is NULL and will never
become NULL again. It is always reassigned to a ftrace tracer.

Several places check if current_trace is NULL before it uses
it, and this check is frivolous, because at the point in time
when the checks are made the only way current_trace could be
NULL is if ftrace failed its allocations at boot up, and the
paths to these locations would probably not be possible.

By initializing current_trace to &nop_trace where it is declared,
current_trace will never be NULL, and we can remove all these
checks of current_trace being NULL which never needed to be
checked in the first place.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace.c |   30 ++++++++++++------------------
 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 70dce64..5d520b7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -249,7 +249,7 @@ static unsigned long		trace_buf_size = TRACE_BUF_SIZE_DEFAULT;
 static struct tracer		*trace_types __read_mostly;
 
 /* current_trace points to the tracer that is currently active */
-static struct tracer		*current_trace __read_mostly;
+static struct tracer		*current_trace __read_mostly = &nop_trace;
 
 /*
  * trace_types_lock is used to protect the trace_types list.
@@ -2100,8 +2100,7 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter)
 	unsigned long total;
 	const char *name = "preemption";
 
-	if (type)
-		name = type->name;
+	name = type->name;
 
 	get_total_entries(tr, &total, &entries);
 
@@ -2477,13 +2476,12 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
 	if (!iter->trace)
 		goto fail;
 
-	if (current_trace)
-		*iter->trace = *current_trace;
+	*iter->trace = *current_trace;
 
 	if (!zalloc_cpumask_var(&iter->started, GFP_KERNEL))
 		goto fail;
 
-	if ((current_trace && current_trace->print_max) || snapshot)
+	if (current_trace->print_max || snapshot)
 		iter->tr = &max_tr;
 	else
 		iter->tr = &global_trace;
@@ -3037,10 +3035,7 @@ tracing_set_trace_read(struct file *filp, char __user *ubuf,
 	int r;
 
 	mutex_lock(&trace_types_lock);
-	if (current_trace)
-		r = sprintf(buf, "%s\n", current_trace->name);
-	else
-		r = sprintf(buf, "\n");
+	r = sprintf(buf, "%s\n", current_trace->name);
 	mutex_unlock(&trace_types_lock);
 
 	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
@@ -3231,10 +3226,10 @@ static int tracing_set_tracer(const char *buf)
 		goto out;
 
 	trace_branch_disable();
-	if (current_trace && current_trace->reset)
+	if (current_trace->reset)
 		current_trace->reset(tr);
 
-	had_max_tr = current_trace && current_trace->allocated_snapshot;
+	had_max_tr = current_trace->allocated_snapshot;
 	current_trace = &nop_trace;
 
 	if (had_max_tr && !t->use_max_tr) {
@@ -3373,8 +3368,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
 		ret = -ENOMEM;
 		goto fail;
 	}
-	if (current_trace)
-		*iter->trace = *current_trace;
+	*iter->trace = *current_trace;
 
 	if (!alloc_cpumask_var(&iter->started, GFP_KERNEL)) {
 		ret = -ENOMEM;
@@ -3525,7 +3519,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 
 	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
-	if (unlikely(current_trace && iter->trace->name != current_trace->name))
+	if (unlikely(iter->trace->name != current_trace->name))
 		*iter->trace = *current_trace;
 	mutex_unlock(&trace_types_lock);
 
@@ -3691,7 +3685,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 
 	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
-	if (unlikely(current_trace && iter->trace->name != current_trace->name))
+	if (unlikely(iter->trace->name != current_trace->name))
 		*iter->trace = *current_trace;
 	mutex_unlock(&trace_types_lock);
 
@@ -4115,7 +4109,7 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 
 	mutex_lock(&trace_types_lock);
 
-	if (current_trace && current_trace->use_max_tr) {
+	if (current_trace->use_max_tr) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -5299,7 +5293,7 @@ __init static int tracer_alloc_buffers(void)
 	init_irq_work(&trace_work_wakeup, trace_wake_up);
 
 	register_tracer(&nop_trace);
-	current_trace = &nop_trace;
+
 	/* All seems OK, enable tracing */
 	tracing_disabled = 0;
 
-- 
1.7.10.4



[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 490 bytes --]

Re: [PATCH 00/11] [GIT PULL] tracing: Various tracing fixes and enhancements

[Ingo Molnar]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> 
> Ingo,
> 
> Please pull the latest tip/perf/core tree, which can be found at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
> tip/perf/core
> 
> Head SHA1: d840f718d28715a9833c1a8f46c2493ff3fd219b
> 
> 
> Hiraku Toyooka (3):
>       tracing: Replace static old_tracer check of tracer name
>       tracing: Make a snapshot feature available from userspace
>       tracing: Add documentation of snapshot utility
> 
> Josh Triplett (1):
>       tracing: Mark tracing_dentry_percpu() static
> 
> Jovi Zhang (1):
>       tracing: Remove second iterator initializer
> 
> Namhyung Kim (1):
>       tracing: Use sched_clock_cpu for trace_clock_global
> 
> Shan Wei (1):
>       tracing: Use __this_cpu_inc/dec operation instead of __get_cpu_var
> 
> Steven Rostedt (1):
>       tracing: Remove tracepoint sample code
> 
> Steven Rostedt (Red Hat) (3):
>       tracing/fgraph: Adjust fgraph depth before calling trace return callback
>       ring-buffer: Add stats field for amount read from trace ring buffer
>       tracing: Init current_trace to nop_trace and remove NULL checks
> 
> ----
>  Documentation/trace/ftrace.txt                 |   83 +++++++++
>  include/linux/ftrace_event.h                   |    3 +
>  include/linux/ring_buffer.h                    |    1 +
>  kernel/trace/Kconfig                           |   10 ++
>  kernel/trace/ring_buffer.c                     |   18 ++
>  kernel/trace/trace.c                           |  222 +++++++++++++++++-------
>  kernel/trace/trace.h                           |    1 +
>  kernel/trace/trace_clock.c                     |    2 +-
>  kernel/trace/trace_functions_graph.c           |    8 +-
>  samples/Kconfig                                |    6 -
>  samples/Makefile                               |    2 +-
>  samples/tracepoints/Makefile                   |    6 -
>  samples/tracepoints/tp-samples-trace.h         |   11 --
>  samples/tracepoints/tracepoint-probe-sample.c  |   57 ------
>  samples/tracepoints/tracepoint-probe-sample2.c |   44 -----
>  samples/tracepoints/tracepoint-sample.c        |   57 ------
>  16 files changed, 288 insertions(+), 243 deletions(-)

Pulled, thanks Steve!

	Ingo