tracing: Have the reg function allow to fail

Some tracepoints have a registration function that gets enabled when the
tracepoint is enabled. There may be cases that the registraction function
must fail (for example, can't allocate enough memory). In this case, the
tracepoint should also fail to register, otherwise the user would not know
why the tracepoint is not working.

Cc: David Howells <dhowells@redhat.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

15 files changed, 34 insertions, 20 deletions

diff --git a/arch/powerpc/include/asm/trace.h b/arch/powerpc/include/asm/trace.h
index 32e36b1..c05cef6 100644
--- a/arch/powerpc/include/asm/trace.h
+++ b/arch/powerpc/include/asm/trace.h
@@ -54,7 +54,7 @@ DEFINE_EVENT(ppc64_interrupt_class, timer_interrupt_exit,
 );
 
 #ifdef CONFIG_PPC_PSERIES
-extern void hcall_tracepoint_regfunc(void);
+extern int hcall_tracepoint_regfunc(void);
 extern void hcall_tracepoint_unregfunc(void);
 
 TRACE_EVENT_FN_COND(hcall_entry,
@@ -104,7 +104,7 @@ TRACE_EVENT_FN_COND(hcall_exit,
 #endif
 
 #ifdef CONFIG_PPC_POWERNV
-extern void opal_tracepoint_regfunc(void);
+extern int opal_tracepoint_regfunc(void);
 extern void opal_tracepoint_unregfunc(void);
 
 TRACE_EVENT_FN(opal_entry,
diff --git a/arch/powerpc/platforms/powernv/opal-tracepoints.c b/arch/powerpc/platforms/powernv/opal-tracepoints.c
index 1e496b7..3c44700 100644
--- a/arch/powerpc/platforms/powernv/opal-tracepoints.c
+++ b/arch/powerpc/platforms/powernv/opal-tracepoints.c
@@ -6,9 +6,10 @@
 #ifdef HAVE_JUMP_LABEL
 struct static_key opal_tracepoint_key = STATIC_KEY_INIT;
 
-void opal_tracepoint_regfunc(void)
+int opal_tracepoint_regfunc(void)
 {
 	static_key_slow_inc(&opal_tracepoint_key);
+	return 0;
 }
 
 void opal_tracepoint_unregfunc(void)
@@ -25,9 +26,10 @@ void opal_tracepoint_unregfunc(void)
 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
 extern long opal_tracepoint_refcount;
 
-void opal_tracepoint_regfunc(void)
+int opal_tracepoint_regfunc(void)
 {
 	opal_tracepoint_refcount++;
+	return 0;
 }
 
 void opal_tracepoint_unregfunc(void)
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index aa35245..c0423ce 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -661,9 +661,10 @@ EXPORT_SYMBOL(arch_free_page);
 #ifdef HAVE_JUMP_LABEL
 struct static_key hcall_tracepoint_key = STATIC_KEY_INIT;
 
-void hcall_tracepoint_regfunc(void)
+int hcall_tracepoint_regfunc(void)
 {
 	static_key_slow_inc(&hcall_tracepoint_key);
+	return 0;
 }
 
 void hcall_tracepoint_unregfunc(void)
@@ -680,9 +681,10 @@ void hcall_tracepoint_unregfunc(void)
 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
 extern long hcall_tracepoint_refcount;
 
-void hcall_tracepoint_regfunc(void)
+int hcall_tracepoint_regfunc(void)
 {
 	hcall_tracepoint_refcount++;
+	return 0;
 }
 
 void hcall_tracepoint_unregfunc(void)
diff --git a/arch/x86/include/asm/trace/exceptions.h b/arch/x86/include/asm/trace/exceptions.h
index 2fbc66c..2422b14 100644
--- a/arch/x86/include/asm/trace/exceptions.h
+++ b/arch/x86/include/asm/trace/exceptions.h
@@ -6,7 +6,7 @@
 
 #include <linux/tracepoint.h>
 
-extern void trace_irq_vector_regfunc(void);
+extern int trace_irq_vector_regfunc(void);
 extern void trace_irq_vector_unregfunc(void);
 
 DECLARE_EVENT_CLASS(x86_exceptions,
diff --git a/arch/x86/include/asm/trace/irq_vectors.h b/arch/x86/include/asm/trace/irq_vectors.h
index 38a09a1..32dd6a9 100644
--- a/arch/x86/include/asm/trace/irq_vectors.h
+++ b/arch/x86/include/asm/trace/irq_vectors.h
@@ -6,7 +6,7 @@
 
 #include <linux/tracepoint.h>
 
-extern void trace_irq_vector_regfunc(void);
+extern int trace_irq_vector_regfunc(void);
 extern void trace_irq_vector_unregfunc(void);
 
 DECLARE_EVENT_CLASS(x86_irq_vector,
diff --git a/arch/x86/kernel/tracepoint.c b/arch/x86/kernel/tracepoint.c
index 1c113db..1551513 100644
--- a/arch/x86/kernel/tracepoint.c
+++ b/arch/x86/kernel/tracepoint.c
@@ -34,7 +34,7 @@ static void switch_idt(void *arg)
 	local_irq_restore(flags);
 }
 
-void trace_irq_vector_regfunc(void)
+int trace_irq_vector_regfunc(void)
 {
 	mutex_lock(&irq_vector_mutex);
 	if (!trace_irq_vector_refcount) {
@@ -44,6 +44,7 @@ void trace_irq_vector_regfunc(void)
 	}
 	trace_irq_vector_refcount++;
 	mutex_unlock(&irq_vector_mutex);
+	return 0;
 }
 
 void trace_irq_vector_unregfunc(void)
diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index b432b64..6a2b995 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -77,9 +77,10 @@ static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);
 static struct static_key i2c_trace_msg = STATIC_KEY_INIT_FALSE;
 static bool is_registered;
 
-void i2c_transfer_trace_reg(void)
+int i2c_transfer_trace_reg(void)
 {
 	static_key_slow_inc(&i2c_trace_msg);
+	return 0;
 }
 
 void i2c_transfer_trace_unreg(void)
diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
index 4ac89acb..a031920 100644
--- a/include/linux/tracepoint-defs.h
+++ b/include/linux/tracepoint-defs.h
@@ -29,7 +29,7 @@ struct tracepoint_func {
 struct tracepoint {
 	const char *name;		/* Tracepoint name */
 	struct static_key key;
-	void (*regfunc)(void);
+	int (*regfunc)(void);
 	void (*unregfunc)(void);
 	struct tracepoint_func __rcu *funcs;
 };
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index be586c6..f72fcfe 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -81,7 +81,7 @@ static inline void tracepoint_synchronize_unregister(void)
 }
 
 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
-extern void syscall_regfunc(void);
+extern int syscall_regfunc(void);
 extern void syscall_unregfunc(void);
 #endif /* CONFIG_HAVE_SYSCALL_TRACEPOINTS */
 
diff --git a/include/trace/events/i2c.h b/include/trace/events/i2c.h
index fe17187..4abb8ea 100644
--- a/include/trace/events/i2c.h
+++ b/include/trace/events/i2c.h
@@ -20,7 +20,7 @@
 /*
  * drivers/i2c/i2c-core.c
  */
-extern void i2c_transfer_trace_reg(void);
+extern int i2c_transfer_trace_reg(void);
 extern void i2c_transfer_trace_unreg(void);
 
 /*
diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c
index 0f109c4..f76d041 100644
--- a/kernel/trace/trace_benchmark.c
+++ b/kernel/trace/trace_benchmark.c
@@ -164,11 +164,12 @@ static int benchmark_event_kthread(void *arg)
  * When the benchmark tracepoint is enabled, it calls this
  * function and the thread that calls the tracepoint is created.
  */
-void trace_benchmark_reg(void)
+int trace_benchmark_reg(void)
 {
 	bm_event_thread = kthread_run(benchmark_event_kthread,
 				      NULL, "event_benchmark");
 	WARN_ON(!bm_event_thread);
+	return 0;
 }
 
 /*
diff --git a/kernel/trace/trace_benchmark.h b/kernel/trace/trace_benchmark.h
index 3c1df1df..ebdbfc2 100644
--- a/kernel/trace/trace_benchmark.h
+++ b/kernel/trace/trace_benchmark.h
@@ -6,7 +6,7 @@
 
 #include <linux/tracepoint.h>
 
-extern void trace_benchmark_reg(void);
+extern int trace_benchmark_reg(void);
 extern void trace_benchmark_unreg(void);
 
 #define BENCHMARK_EVENT_STRLEN		128
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index d0639d9..1f9a31f 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -194,9 +194,13 @@ static int tracepoint_add_func(struct tracepoint *tp,
 			       struct tracepoint_func *func, int prio)
 {
 	struct tracepoint_func *old, *tp_funcs;
+	int ret;
 
-	if (tp->regfunc && !static_key_enabled(&tp->key))
-		tp->regfunc();
+	if (tp->regfunc && !static_key_enabled(&tp->key)) {
+		ret = tp->regfunc();
+		if (ret < 0)
+			return ret;
+	}
 
 	tp_funcs = rcu_dereference_protected(tp->funcs,
 			lockdep_is_held(&tracepoints_mutex));
@@ -529,7 +533,7 @@ EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
 static int sys_tracepoint_refcount;
 
-void syscall_regfunc(void)
+int syscall_regfunc(void)
 {
 	struct task_struct *p, *t;
 
@@ -541,6 +545,8 @@ void syscall_regfunc(void)
 		read_unlock(&tasklist_lock);
 	}
 	sys_tracepoint_refcount++;
+
+	return 0;
 }
 
 void syscall_unregfunc(void)
diff --git a/samples/trace_events/trace-events-sample.c b/samples/trace_events/trace-events-sample.c
index 880a7d1..30e282d 100644
--- a/samples/trace_events/trace-events-sample.c
+++ b/samples/trace_events/trace-events-sample.c
@@ -79,7 +79,7 @@ static int simple_thread_fn(void *arg)
 
 static DEFINE_MUTEX(thread_mutex);
 
-void foo_bar_reg(void)
+int foo_bar_reg(void)
 {
 	pr_info("Starting thread for foo_bar_fn\n");
 	/*
@@ -90,6 +90,7 @@ void foo_bar_reg(void)
 	mutex_lock(&thread_mutex);
 	simple_tsk_fn = kthread_run(simple_thread_fn, NULL, "event-sample-fn");
 	mutex_unlock(&thread_mutex);
+	return 0;
 }
 
 void foo_bar_unreg(void)
diff --git a/samples/trace_events/trace-events-sample.h b/samples/trace_events/trace-events-sample.h
index d6b75bb..76a75ab 100644
--- a/samples/trace_events/trace-events-sample.h
+++ b/samples/trace_events/trace-events-sample.h
@@ -354,7 +354,7 @@ TRACE_EVENT_CONDITION(foo_bar_with_cond,
 	TP_printk("foo %s %d", __get_str(foo), __entry->bar)
 );
 
-void foo_bar_reg(void);
+int foo_bar_reg(void);
 void foo_bar_unreg(void);
 
 /*