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 <[e-mail]>
Cc: Seiji Aguchi <[e-mail]>
Cc: Anton Blanchard <[e-mail]>
Cc: Mathieu Desnoyers <[e-mail]>
Signed-off-by: Steven Rostedt <[e-mail]>

arch/powerpc/include/asm/trace.h

···
 );
 
 #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,
···
 #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,

arch/powerpc/platforms/powernv/opal-tracepoints.c

···
 #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)
···
 /* 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)

arch/powerpc/platforms/pseries/lpar.c

···
 #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)
···
 /* 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)

arch/x86/include/asm/trace/exceptions.h

···
 
 #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,

arch/x86/include/asm/trace/irq_vectors.h

···
 
 #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,

arch/x86/kernel/tracepoint.c

···
 	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) {
···
 	}
 	trace_irq_vector_refcount++;
 	mutex_unlock(&irq_vector_mutex);
+	return 0;
 }
 
 void trace_irq_vector_unregfunc(void)

drivers/i2c/i2c-core.c

···
 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)

include/linux/tracepoint-defs.h

···
 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;
 };

include/linux/tracepoint.h

···
 }
 
 #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 */
 

include/trace/events/i2c.h

···
 /*
  * 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);
 
 /*

kernel/trace/trace_benchmark.c

···
  * 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;
 }
 
 /*

kernel/trace/trace_benchmark.h

···
 
 #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

kernel/tracepoint.c

···
 			       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));
···
 /* 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;
 
···
 		read_unlock(&tasklist_lock);
 	}
 	sys_tracepoint_refcount++;
+
+	return 0;
 }
 
 void syscall_unregfunc(void)

samples/trace_events/trace-events-sample.c

···
 
 static DEFINE_MUTEX(thread_mutex);
 
-void foo_bar_reg(void)
+int foo_bar_reg(void)
 {
 	pr_info("Starting thread for foo_bar_fn\n");
 	/*
···
 	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)

samples/trace_events/trace-events-sample.h

···
 	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);
 
 /*