tracing/osnoise: Support a list of trace_array *tr

osnoise/timerlat were built to run a single instance, and for this,
a single variable is enough to store the current struct trace_array
*tr with information about the tracing instance. This is done via
the *osnoise_trace variable. A trace_array represents a trace instance.

In preparation to support multiple instances, replace the
*osnoise_trace variable with an RCU protected list of instances.

The operations that refer to an instance now propagate to all
elements of the list (all instances).

Also, replace the osnoise_busy variable with a check if the list
has elements (busy).

No functional change is expected with this patch, i.e., only one
instance is allowed yet.

Link: https://lkml.kernel.org/r/91d006e889b9a5d1ff258fe6077f021ae3f26372.1635702894.git.bristot@kernel.org

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: linux-rt-users@vger.kernel.org
Cc: linux-trace-devel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_osnoise.c

@@ -38,8 +38,6 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/osnoise.h>
 
-static struct trace_array	*osnoise_trace;
-
 /*
  * Default values.
  */
@@ -50,6 +48,81 @@ static struct trace_array	*osnoise_trace;
 #define DEFAULT_TIMERLAT_PERIOD	1000			/* 1ms */
 #define DEFAULT_TIMERLAT_PRIO	95			/* FIFO 95 */
 
+/*
+ * trace_array of the enabled osnoise/timerlat instances.
+ */
+struct osnoise_instance {
+	struct list_head	list;
+	struct trace_array	*tr;
+};
+struct list_head osnoise_instances;
+
+static bool osnoise_has_registered_instances(void)
+{
+	return !!list_first_or_null_rcu(&osnoise_instances,
+					struct osnoise_instance,
+					list);
+}
+
+/*
+ * osnoise_register_instance - register a new trace instance
+ *
+ * Register a trace_array *tr in the list of instances running
+ * osnoise/timerlat tracers.
+ */
+static int osnoise_register_instance(struct trace_array *tr)
+{
+	struct osnoise_instance *inst;
+
+	/*
+	 * register/unregister serialization is provided by trace's
+	 * trace_types_lock.
+	 */
+	lockdep_assert_held(&trace_types_lock);
+
+	inst = kmalloc(sizeof(*inst), GFP_KERNEL);
+	if (!inst)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD_RCU(&inst->list);
+	inst->tr = tr;
+	list_add_tail_rcu(&inst->list, &osnoise_instances);
+
+	return 0;
+}
+
+/*
+ *  osnoise_unregister_instance - unregister a registered trace instance
+ *
+ * Remove the trace_array *tr from the list of instances running
+ * osnoise/timerlat tracers.
+ */
+static void osnoise_unregister_instance(struct trace_array *tr)
+{
+	struct osnoise_instance *inst;
+	int found = 0;
+
+	/*
+	 * register/unregister serialization is provided by trace's
+	 * trace_types_lock.
+	 */
+	lockdep_assert_held(&trace_types_lock);
+
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		if (inst->tr == tr) {
+			list_del_rcu(&inst->list);
+			found = 1;
+			break;
+		}
+	}
+
+	if (!found)
+		return;
+
+	synchronize_rcu();
+	kfree(inst);
+}
+
 /*
  * NMI runtime info.
  */
@@ -248,11 +321,6 @@ static struct osnoise_data {
 #endif
 };
 
-/*
- * Boolean variable used to inform that the tracer is currently sampling.
- */
-static bool osnoise_busy;
-
 #ifdef CONFIG_PREEMPT_RT
 /*
  * Print the osnoise header info.
@@ -315,19 +383,24 @@ static void print_osnoise_headers(struct seq_file *s)
  * osnoise_taint - report an osnoise error.
  */
 #define osnoise_taint(msg) ({							\
-	struct trace_array *tr = osnoise_trace;					\
+	struct osnoise_instance *inst;						\
+	struct trace_buffer *buffer;						\
 										\
-	trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_, msg);	\
+	rcu_read_lock();							\
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {		\
+		buffer = inst->tr->array_buffer.buffer;				\
+		trace_array_printk_buf(buffer, _THIS_IP_, msg);			\
+	}									\
+	rcu_read_unlock();							\
 	osnoise_data.tainted = true;						\
 })
 
 /*
  * Record an osnoise_sample into the tracer buffer.
  */
-static void trace_osnoise_sample(struct osnoise_sample *sample)
+static void
+__trace_osnoise_sample(struct osnoise_sample *sample, struct trace_buffer *buffer)
 {
-	struct trace_array *tr = osnoise_trace;
-	struct trace_buffer *buffer = tr->array_buffer.buffer;
 	struct trace_event_call *call = &event_osnoise;
 	struct ring_buffer_event *event;
 	struct osnoise_entry *entry;
@@ -350,6 +423,22 @@ static void trace_osnoise_sample(struct osnoise_sample *sample)
 		trace_buffer_unlock_commit_nostack(buffer, event);
 }
 
+/*
+ * Record an osnoise_sample on all osnoise instances.
+ */
+static void trace_osnoise_sample(struct osnoise_sample *sample)
+{
+	struct osnoise_instance *inst;
+	struct trace_buffer *buffer;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		buffer = inst->tr->array_buffer.buffer;
+		__trace_osnoise_sample(sample, buffer);
+	}
+	rcu_read_unlock();
+}
+
 #ifdef CONFIG_TIMERLAT_TRACER
 /*
  * Print the timerlat header info.
@@ -388,14 +477,10 @@ static void print_timerlat_headers(struct seq_file *s)
 }
 #endif /* CONFIG_PREEMPT_RT */
 
-/*
- * Record an timerlat_sample into the tracer buffer.
- */
-static void trace_timerlat_sample(struct timerlat_sample *sample)
+static void
+__trace_timerlat_sample(struct timerlat_sample *sample, struct trace_buffer *buffer)
 {
-	struct trace_array *tr = osnoise_trace;
 	struct trace_event_call *call = &event_osnoise;
-	struct trace_buffer *buffer = tr->array_buffer.buffer;
 	struct ring_buffer_event *event;
 	struct timerlat_entry *entry;
 
@@ -412,6 +497,22 @@ static void trace_timerlat_sample(struct timerlat_sample *sample)
 		trace_buffer_unlock_commit_nostack(buffer, event);
 }
 
+/*
+ * Record an timerlat_sample into the tracer buffer.
+ */
+static void trace_timerlat_sample(struct timerlat_sample *sample)
+{
+	struct osnoise_instance *inst;
+	struct trace_buffer *buffer;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		buffer = inst->tr->array_buffer.buffer;
+		__trace_timerlat_sample(sample, buffer);
+	}
+	rcu_read_unlock();
+}
+
 #ifdef CONFIG_STACKTRACE
 
 #define	MAX_CALLS	256
@@ -451,29 +552,18 @@ static void timerlat_save_stack(int skip)
 	return;
 
 }
-/*
- * timerlat_dump_stack - dump a stack trace previously saved
- *
- * Dump a saved stack trace into the trace buffer.
- */
-static void timerlat_dump_stack(void)
+
+static void
+__timerlat_dump_stack(struct trace_buffer *buffer, struct trace_stack *fstack, unsigned int size)
 {
 	struct trace_event_call *call = &event_osnoise;
-	struct trace_array *tr = osnoise_trace;
-	struct trace_buffer *buffer = tr->array_buffer.buffer;
 	struct ring_buffer_event *event;
-	struct trace_stack *fstack;
 	struct stack_entry *entry;
-	unsigned int size;
-
-	preempt_disable_notrace();
-	fstack = this_cpu_ptr(&trace_stack);
-	size = fstack->stack_size;
 
 	event = trace_buffer_lock_reserve(buffer, TRACE_STACK, sizeof(*entry) + size,
 					  tracing_gen_ctx());
 	if (!event)
-		goto out;
+		return;
 
 	entry = ring_buffer_event_data(event);
 
@@ -482,8 +572,29 @@ static void timerlat_dump_stack(void)
 
 	if (!call_filter_check_discard(call, entry, buffer, event))
 		trace_buffer_unlock_commit_nostack(buffer, event);
+}
 
-out:
+/*
+ * timerlat_dump_stack - dump a stack trace previously saved
+ */
+static void timerlat_dump_stack(void)
+{
+	struct osnoise_instance *inst;
+	struct trace_buffer *buffer;
+	struct trace_stack *fstack;
+	unsigned int size;
+
+	preempt_disable_notrace();
+	fstack = this_cpu_ptr(&trace_stack);
+	size = fstack->stack_size;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		buffer = inst->tr->array_buffer.buffer;
+		__timerlat_dump_stack(buffer, fstack, size);
+
+	}
+	rcu_read_unlock();
 	preempt_enable_notrace();
 }
 #else
@@ -1078,12 +1189,37 @@ diff_osn_sample_stats(struct osnoise_variables *osn_var, struct osnoise_sample *
  */
 static __always_inline void osnoise_stop_tracing(void)
 {
-	struct trace_array *tr = osnoise_trace;
+	struct osnoise_instance *inst;
+	struct trace_array *tr;
 
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		tr = inst->tr;
 		trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_,
 				"stop tracing hit on cpu %d\n", smp_processor_id());
 
 		tracer_tracing_off(tr);
+	}
+	rcu_read_unlock();
+}
+
+/*
+ * notify_new_max_latency - Notify a new max latency via fsnotify interface.
+ */
+static void notify_new_max_latency(u64 latency)
+{
+	struct osnoise_instance *inst;
+	struct trace_array *tr;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		tr = inst->tr;
+		if (tr->max_latency < latency) {
+			tr->max_latency = latency;
+			latency_fsnotify(tr);
+		}
+	}
+	rcu_read_unlock();
 }
 
 /*
@@ -1097,7 +1233,6 @@ static __always_inline void osnoise_stop_tracing(void)
 static int run_osnoise(void)
 {
 	struct osnoise_variables *osn_var = this_cpu_osn_var();
-	struct trace_array *tr = osnoise_trace;
 	u64 start, sample, last_sample;
 	u64 last_int_count, int_count;
 	s64 noise = 0, max_noise = 0;
@@ -1232,11 +1367,7 @@ static int run_osnoise(void)
 
 	trace_osnoise_sample(&s);
 
-	/* Keep a running maximum ever recorded osnoise "latency" */
-	if (max_noise > tr->max_latency) {
-		tr->max_latency = max_noise;
-		latency_fsnotify(tr);
-	}
+	notify_new_max_latency(max_noise);
 
 	if (osnoise_data.stop_tracing_total)
 		if (s.noise > osnoise_data.stop_tracing_total)
@@ -1294,7 +1425,6 @@ static int osnoise_main(void *data)
 static enum hrtimer_restart timerlat_irq(struct hrtimer *timer)
 {
 	struct osnoise_variables *osn_var = this_cpu_osn_var();
-	struct trace_array *tr = osnoise_trace;
 	struct timerlat_variables *tlat;
 	struct timerlat_sample s;
 	u64 now;
@@ -1365,11 +1495,7 @@ static enum hrtimer_restart timerlat_irq(struct hrtimer *timer)
 
 	trace_timerlat_sample(&s);
 
-	/* Keep a running maximum ever recorded os noise "latency" */
-	if (diff > tr->max_latency) {
-		tr->max_latency = diff;
-		latency_fsnotify(tr);
-	}
+	notify_new_max_latency(diff);
 
 	if (osnoise_data.stop_tracing)
 		if (time_to_us(diff) >= osnoise_data.stop_tracing)
@@ -1581,7 +1707,7 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)
 
 	mutex_lock(&trace_types_lock);
 
-	if (!osnoise_busy)
+	if (!osnoise_has_registered_instances())
 		goto out_unlock_trace;
 
 	mutex_lock(&interface_lock);
@@ -1716,11 +1842,10 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 		goto err_free;
 
 	/*
-	 * trace_types_lock is taken to avoid concurrency on start/stop
-	 * and osnoise_busy.
+	 * trace_types_lock is taken to avoid concurrency on start/stop.
 	 */
 	mutex_lock(&trace_types_lock);
-	running = osnoise_busy;
+	running = osnoise_has_registered_instances();
 	if (running)
 		stop_per_cpu_kthreads();
 
@@ -1943,8 +2068,6 @@ static int osnoise_workload_start(void)
 		return retval;
 	}
 
-	osnoise_busy = true;
-
 	return 0;
 }
 
@@ -1953,7 +2076,7 @@ static int osnoise_workload_start(void)
  */
 static void osnoise_workload_stop(void)
 {
-	if (!osnoise_busy)
+	if (osnoise_has_registered_instances())
 		return;
 
 	trace_osnoise_callback_enabled = false;
@@ -1968,28 +2091,28 @@ static void osnoise_workload_stop(void)
 	unhook_irq_events();
 	unhook_softirq_events();
 	unhook_thread_events();
-
-	osnoise_busy = false;
 }
 
 static void osnoise_tracer_start(struct trace_array *tr)
 {
 	int retval;
 
-	if (osnoise_busy)
+	if (osnoise_has_registered_instances())
 		return;
 
 	retval = osnoise_workload_start();
 	if (retval)
 		pr_err(BANNER "Error starting osnoise tracer\n");
 
+	osnoise_register_instance(tr);
 }
 
 static void osnoise_tracer_stop(struct trace_array *tr)
 {
-	if (!osnoise_busy)
+	if (!osnoise_has_registered_instances())
 		return;
 
+	osnoise_unregister_instance(tr);
 	osnoise_workload_stop();
 }
 
@@ -1997,14 +2120,12 @@ static int osnoise_tracer_init(struct trace_array *tr)
 {
 
 	/* Only allow one instance to enable this */
-	if (osnoise_busy)
+	if (osnoise_has_registered_instances())
 		return -EBUSY;
 
-	osnoise_trace = tr;
 	tr->max_latency = 0;
 
 	osnoise_tracer_start(tr);
-
 	return 0;
 }
 
@@ -2028,7 +2149,7 @@ static void timerlat_tracer_start(struct trace_array *tr)
 {
 	int retval;
 
-	if (osnoise_busy)
+	if (osnoise_has_registered_instances())
 		return;
 
 	osnoise_data.timerlat_tracer = 1;
@@ -2037,6 +2158,8 @@ static void timerlat_tracer_start(struct trace_array *tr)
 	if (retval)
 		goto out_err;
 
+	osnoise_register_instance(tr);
+
 	return;
 out_err:
 	pr_err(BANNER "Error starting timerlat tracer\n");
@@ -2046,7 +2169,7 @@ static void timerlat_tracer_stop(struct trace_array *tr)
 {
 	int cpu;
 
-	if (!osnoise_busy)
+	if (!osnoise_has_registered_instances())
 		return;
 
 	for_each_online_cpu(cpu)
@@ -2060,11 +2183,9 @@ static void timerlat_tracer_stop(struct trace_array *tr)
 static int timerlat_tracer_init(struct trace_array *tr)
 {
 	/* Only allow one instance to enable this */
-	if (osnoise_busy)
+	if (osnoise_has_registered_instances())
 		return -EBUSY;
 
-	osnoise_trace = tr;
-
 	tr->max_latency = 0;
 
 	timerlat_tracer_start(tr);
@@ -2111,6 +2232,8 @@ __init static int init_osnoise_tracer(void)
 #endif
 	osnoise_init_hotplug_support();
 
+	INIT_LIST_HEAD_RCU(&osnoise_instances);
+
 	init_tracefs();
 
 	return 0;