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Subject[PATCH 2/4] tracing/ftrace: Change the type of the init() callback
Impact: Handle errors during initialization of a tracer

This bring a way to know if the initialization of a tracer successed.
A tracer must return 0 on success and a traditional error (ie: -ENOMEM)
if it fails.
If a tracer fails to init, it is free to print a detailed warn. The tracing
api will not and switch to a new tracer will just return the error from the init
callback.

Note: this will be used for the return tracer.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Pekka Paalanen <pq@iki.fi>
Cc: Steven Noonan <steven@uplinklabs.net>
---
kernel/trace/trace.c | 7 ++-
kernel/trace/trace.h | 3 +-
kernel/trace/trace_boot.c | 3 +-
kernel/trace/trace_branch.c | 3 +-
kernel/trace/trace_functions.c | 3 +-
kernel/trace/trace_functions_return.c | 3 +-
kernel/trace/trace_irqsoff.c | 9 +++-
kernel/trace/trace_mmiotrace.c | 3 +-
kernel/trace/trace_nop.c | 3 +-
kernel/trace/trace_sched_switch.c | 3 +-
kernel/trace/trace_sched_wakeup.c | 3 +-
kernel/trace/trace_selftest.c | 66 ++++++++++++++++++++++++++++----
kernel/trace/trace_sysprof.c | 3 +-
13 files changed, 88 insertions(+), 24 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2d5672d..938ee31 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2638,8 +2638,11 @@ static int tracing_set_tracer(char *buf)
current_trace->reset(tr);

current_trace = t;
- if (t->init)
- t->init(tr);
+ if (t->init) {
+ ret = t->init(tr);
+ if (ret)
+ goto out;
+ }

trace_branch_enable(tr);
out:
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 790ea8c..cdbd5cc 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -264,7 +264,8 @@ enum print_line_t {
*/
struct tracer {
const char *name;
- void (*init)(struct trace_array *tr);
+ /* Your tracer should raise a warning if init fails */
+ int (*init)(struct trace_array *tr);
void (*reset)(struct trace_array *tr);
void (*start)(struct trace_array *tr);
void (*stop)(struct trace_array *tr);
diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index cb333b7..a4fa2c5 100644
--- a/kernel/trace/trace_boot.c
+++ b/kernel/trace/trace_boot.c
@@ -47,7 +47,7 @@ static void reset_boot_trace(struct trace_array *tr)
tracing_reset(tr, cpu);
}

-static void boot_trace_init(struct trace_array *tr)
+static int boot_trace_init(struct trace_array *tr)
{
int cpu;
boot_trace = tr;
@@ -56,6 +56,7 @@ static void boot_trace_init(struct trace_array *tr)
tracing_reset(tr, cpu);

tracing_sched_switch_assign_trace(tr);
+ return 0;
}

static enum print_line_t
diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index 8526555..44bd395 100644
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -125,7 +125,7 @@ static void stop_branch_trace(struct trace_array *tr)
disable_branch_tracing();
}

-static void branch_trace_init(struct trace_array *tr)
+static int branch_trace_init(struct trace_array *tr)
{
int cpu;

@@ -133,6 +133,7 @@ static void branch_trace_init(struct trace_array *tr)
tracing_reset(tr, cpu);

start_branch_trace(tr);
+ return 0;
}

static void branch_trace_reset(struct trace_array *tr)
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 8693b7a..e74f6d0 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -42,9 +42,10 @@ static void stop_function_trace(struct trace_array *tr)
tracing_stop_cmdline_record();
}

-static void function_trace_init(struct trace_array *tr)
+static int function_trace_init(struct trace_array *tr)
{
start_function_trace(tr);
+ return 0;
}

static void function_trace_reset(struct trace_array *tr)
diff --git a/kernel/trace/trace_functions_return.c b/kernel/trace/trace_functions_return.c
index 7680b21..61185f7 100644
--- a/kernel/trace/trace_functions_return.c
+++ b/kernel/trace/trace_functions_return.c
@@ -24,13 +24,14 @@ static void stop_return_trace(struct trace_array *tr)
unregister_ftrace_return();
}

-static void return_trace_init(struct trace_array *tr)
+static int return_trace_init(struct trace_array *tr)
{
int cpu;
for_each_online_cpu(cpu)
tracing_reset(tr, cpu);

start_return_trace(tr);
+ return 0;
}

static void return_trace_reset(struct trace_array *tr)
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index d919d4e..7c2e326 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -416,11 +416,12 @@ static void irqsoff_tracer_close(struct trace_iterator *iter)
}

#ifdef CONFIG_IRQSOFF_TRACER
-static void irqsoff_tracer_init(struct trace_array *tr)
+static int irqsoff_tracer_init(struct trace_array *tr)
{
trace_type = TRACER_IRQS_OFF;

__irqsoff_tracer_init(tr);
+ return 0;
}
static struct tracer irqsoff_tracer __read_mostly =
{
@@ -442,11 +443,12 @@ static struct tracer irqsoff_tracer __read_mostly =
#endif

#ifdef CONFIG_PREEMPT_TRACER
-static void preemptoff_tracer_init(struct trace_array *tr)
+static int preemptoff_tracer_init(struct trace_array *tr)
{
trace_type = TRACER_PREEMPT_OFF;

__irqsoff_tracer_init(tr);
+ return 0;
}

static struct tracer preemptoff_tracer __read_mostly =
@@ -471,11 +473,12 @@ static struct tracer preemptoff_tracer __read_mostly =
#if defined(CONFIG_IRQSOFF_TRACER) && \
defined(CONFIG_PREEMPT_TRACER)

-static void preemptirqsoff_tracer_init(struct trace_array *tr)
+static int preemptirqsoff_tracer_init(struct trace_array *tr)
{
trace_type = TRACER_IRQS_OFF | TRACER_PREEMPT_OFF;

__irqsoff_tracer_init(tr);
+ return 0;
}

static struct tracer preemptirqsoff_tracer __read_mostly =
diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
index 51bcf37..433d650 100644
--- a/kernel/trace/trace_mmiotrace.c
+++ b/kernel/trace/trace_mmiotrace.c
@@ -30,13 +30,14 @@ static void mmio_reset_data(struct trace_array *tr)
tracing_reset(tr, cpu);
}

-static void mmio_trace_init(struct trace_array *tr)
+static int mmio_trace_init(struct trace_array *tr)
{
pr_debug("in %s\n", __func__);
mmio_trace_array = tr;

mmio_reset_data(tr);
enable_mmiotrace();
+ return 0;
}

static void mmio_trace_reset(struct trace_array *tr)
diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
index 2ef1d22..0e77415 100644
--- a/kernel/trace/trace_nop.c
+++ b/kernel/trace/trace_nop.c
@@ -24,7 +24,7 @@ static void stop_nop_trace(struct trace_array *tr)
/* Nothing to do! */
}

-static void nop_trace_init(struct trace_array *tr)
+static int nop_trace_init(struct trace_array *tr)
{
int cpu;
ctx_trace = tr;
@@ -33,6 +33,7 @@ static void nop_trace_init(struct trace_array *tr)
tracing_reset(tr, cpu);

start_nop_trace(tr);
+ return 0;
}

static void nop_trace_reset(struct trace_array *tr)
diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index be35bdf..8633905 100644
--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -206,10 +206,11 @@ static void stop_sched_trace(struct trace_array *tr)
tracing_stop_sched_switch_record();
}

-static void sched_switch_trace_init(struct trace_array *tr)
+static int sched_switch_trace_init(struct trace_array *tr)
{
ctx_trace = tr;
start_sched_trace(tr);
+ return 0;
}

static void sched_switch_trace_reset(struct trace_array *tr)
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 983f2b1..0067b49 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -331,10 +331,11 @@ static void stop_wakeup_tracer(struct trace_array *tr)
unregister_trace_sched_wakeup(probe_wakeup);
}

-static void wakeup_tracer_init(struct trace_array *tr)
+static int wakeup_tracer_init(struct trace_array *tr)
{
wakeup_trace = tr;
start_wakeup_tracer(tr);
+ return 0;
}

static void wakeup_tracer_reset(struct trace_array *tr)
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 24e6e07..c9fa616 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -71,6 +71,11 @@ static int trace_test_buffer(struct trace_array *tr, unsigned long *count)
return ret;
}

+static inline void warn_failed_init_tracer(struct tracer *trace, int init_ret)
+{
+ printk(KERN_WARNING "Failed to init %s tracer, init returned %d\n",
+ trace->name, init_ret);
+}
#ifdef CONFIG_FUNCTION_TRACER

#ifdef CONFIG_DYNAMIC_FTRACE
@@ -111,7 +116,11 @@ int trace_selftest_startup_dynamic_tracing(struct tracer *trace,
ftrace_set_filter(func_name, strlen(func_name), 1);

/* enable tracing */
- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ goto out;
+ }

/* Sleep for a 1/10 of a second */
msleep(100);
@@ -181,7 +190,12 @@ trace_selftest_startup_function(struct tracer *trace, struct trace_array *tr)
ftrace_enabled = 1;
tracer_enabled = 1;

- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ goto out;
+ }
+
/* Sleep for a 1/10 of a second */
msleep(100);
/* stop the tracing. */
@@ -223,7 +237,12 @@ trace_selftest_startup_irqsoff(struct tracer *trace, struct trace_array *tr)
int ret;

/* start the tracing */
- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ return ret;
+ }
+
/* reset the max latency */
tracing_max_latency = 0;
/* disable interrupts for a bit */
@@ -272,7 +291,12 @@ trace_selftest_startup_preemptoff(struct tracer *trace, struct trace_array *tr)
}

/* start the tracing */
- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ return ret;
+ }
+
/* reset the max latency */
tracing_max_latency = 0;
/* disable preemption for a bit */
@@ -321,7 +345,11 @@ trace_selftest_startup_preemptirqsoff(struct tracer *trace, struct trace_array *
}

/* start the tracing */
- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ goto out;
+ }

/* reset the max latency */
tracing_max_latency = 0;
@@ -449,7 +477,12 @@ trace_selftest_startup_wakeup(struct tracer *trace, struct trace_array *tr)
wait_for_completion(&isrt);

/* start the tracing */
- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ return ret;
+ }
+
/* reset the max latency */
tracing_max_latency = 0;

@@ -505,7 +538,12 @@ trace_selftest_startup_sched_switch(struct tracer *trace, struct trace_array *tr
int ret;

/* start the tracing */
- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ return ret;
+ }
+
/* Sleep for a 1/10 of a second */
msleep(100);
/* stop the tracing. */
@@ -532,7 +570,12 @@ trace_selftest_startup_sysprof(struct tracer *trace, struct trace_array *tr)
int ret;

/* start the tracing */
- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ return 0;
+ }
+
/* Sleep for a 1/10 of a second */
msleep(100);
/* stop the tracing. */
@@ -554,7 +597,12 @@ trace_selftest_startup_branch(struct tracer *trace, struct trace_array *tr)
int ret;

/* start the tracing */
- trace->init(tr);
+ ret = trace->init(tr);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ return ret;
+ }
+
/* Sleep for a 1/10 of a second */
msleep(100);
/* stop the tracing. */
diff --git a/kernel/trace/trace_sysprof.c b/kernel/trace/trace_sysprof.c
index dc2f690..a10a8dc 100644
--- a/kernel/trace/trace_sysprof.c
+++ b/kernel/trace/trace_sysprof.c
@@ -261,11 +261,12 @@ static void stop_stack_trace(struct trace_array *tr)
mutex_unlock(&sample_timer_lock);
}

-static void stack_trace_init(struct trace_array *tr)
+static int stack_trace_init(struct trace_array *tr)
{
sysprof_trace = tr;

start_stack_trace(tr);
+ return 0;
}

static void stack_trace_reset(struct trace_array *tr)
--
1.5.2.5

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