tracing/ftrace: change the type of the init() callback

Impact: extend the ->init() method with the ability to fail

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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

13 files changed, 88 insertions, 24 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 80898f4870cc..396fda034e3f 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 790ea8c0e1f3..cdbd5cc22be8 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 cb333b7fd113..a4fa2c57e34e 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 85265553918f..44bd39539d61 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 8693b7a0a5b2..e74f6d0a3216 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 7680b21537dd..61185f756a13 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 d919d4eaa7cc..7c2e326bbc8b 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 51bcf370215e..433d650eda9f 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 2ef1d227e7d8..0e77415caed3 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 be35bdfe2e38..863390557b44 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 983f2b1478c9..0067b49746c1 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 5cb64ea061b5..88c8eb70f54a 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 05f753422aea..54960edb96d0 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)