Merge tag 'trace-v5.16-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull more tracing updates from Steven Rostedt:

- osnoise and timerlat updates that will work with the RTLA tool
(Real-Time Linux Analysis).

Specifically it disconnects the work load (threads that look for
latency) from the tracing instances attached to them, allowing for
more than one instance to retrieve data from the work load.

- Optimization on division in the trace histogram trigger code to use
shift and multiply when possible. Also added documentation.

- Fix prototype to my_direct_func in direct ftrace trampoline sample
code.

* tag 'trace-v5.16-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
ftrace/samples: Add missing prototype for my_direct_func
tracing/selftests: Add tests for hist trigger expression parsing
tracing/histogram: Document hist trigger variables
tracing/histogram: Update division by 0 documentation
tracing/histogram: Optimize division by constants
tracing/osnoise: Remove PREEMPT_RT ifdefs from inside functions
tracing/osnoise: Remove STACKTRACE ifdefs from inside functions
tracing/osnoise: Allow multiple instances of the same tracer
tracing/osnoise: Remove TIMERLAT ifdefs from inside functions
tracing/osnoise: Support a list of trace_array *tr
tracing/osnoise: Use start/stop_per_cpu_kthreads() on osnoise_cpus_write()
tracing/osnoise: Split workload start from the tracer start
tracing/osnoise: Improve comments about barrier need for NMI callbacks
tracing/osnoise: Do not follow tracing_cpumask

Documentation/trace/histogram.rst

···
 Expressions support the use of addition, subtraction, multiplication and
 division operators (+-\*/).
 
-Note that division by zero always returns -1.
+Note if division by zero cannot be detected at parse time (i.e. the
+divisor is not a constant), the result will be -1.
 
 Numeric constants can also be used directly in an expression::
 

kernel/trace/trace.c

···
 #ifdef CONFIG_HIST_TRIGGERS
 	"      hist trigger\t- If set, event hits are aggregated into a hash table\n"
 	"\t    Format: hist:keys=<field1[,field2,...]>\n"
+	"\t            [:<var1>=<field|var_ref|numeric_literal>[,<var2>=...]]\n"
 	"\t            [:values=<field1[,field2,...]>]\n"
 	"\t            [:sort=<field1[,field2,...]>]\n"
 	"\t            [:size=#entries]\n"
···
 	"\t    Note, special fields can be used as well:\n"
 	"\t            common_timestamp - to record current timestamp\n"
 	"\t            common_cpu - to record the CPU the event happened on\n"
+	"\n"
+	"\t    A hist trigger variable can be:\n"
+	"\t        - a reference to a field e.g. x=current_timestamp,\n"
+	"\t        - a reference to another variable e.g. y=$x,\n"
+	"\t        - a numeric literal: e.g. ms_per_sec=1000,\n"
+	"\t        - an arithmetic expression: e.g. time_secs=current_timestamp/1000\n"
+	"\n"
+	"\t    hist trigger aritmethic expressions support addition(+), subtraction(-),\n"
+	"\t    multiplication(*) and division(/) operators. An operand can be either a\n"
+	"\t    variable reference, field or numeric literal.\n"
 	"\n"
 	"\t    When a matching event is hit, an entry is added to a hash\n"
 	"\t    table using the key(s) and value(s) named, and the value of a\n"

kernel/trace/trace_events_hist.c

···
 	C(INVALID_SORT_FIELD,	"Sort field must be a key or a val"),	\
 	C(INVALID_STR_OPERAND,	"String type can not be an operand in expression"), \
 	C(EXPECT_NUMBER,	"Expecting numeric literal"),		\
-	C(UNARY_MINUS_SUBEXPR,	"Unary minus not supported in sub-expressions"),
+	C(UNARY_MINUS_SUBEXPR,	"Unary minus not supported in sub-expressions"), \
+	C(DIVISION_BY_ZERO,	"Division by zero"),
 
 #undef C
 #define C(a, b)		HIST_ERR_##a
···
 #define HIST_FIELDS_MAX		(TRACING_MAP_FIELDS_MAX + TRACING_MAP_VARS_MAX)
 #define HIST_ACTIONS_MAX	8
 #define HIST_CONST_DIGITS_MAX	21
+#define HIST_DIV_SHIFT		20  /* For optimizing division by constants */
 
 enum field_op_id {
 	FIELD_OP_NONE,
···
 
 	/* Numeric literals are represented as u64 */
 	u64				constant;
+	/* Used to optimize division by constants */
+	u64				div_multiplier;
 };
 
 static u64 hist_field_none(struct hist_field *field,
···
 		return val1 >> __ffs64(val2);
 
 	return div64_u64(val1, val2);
+}
+
+static u64 div_by_power_of_two(struct hist_field *hist_field,
+				struct tracing_map_elt *elt,
+				struct trace_buffer *buffer,
+				struct ring_buffer_event *rbe,
+				void *event)
+{
+	struct hist_field *operand1 = hist_field->operands[0];
+	struct hist_field *operand2 = hist_field->operands[1];
+
+	u64 val1 = operand1->fn(operand1, elt, buffer, rbe, event);
+
+	return val1 >> __ffs64(operand2->constant);
+}
+
+static u64 div_by_not_power_of_two(struct hist_field *hist_field,
+				struct tracing_map_elt *elt,
+				struct trace_buffer *buffer,
+				struct ring_buffer_event *rbe,
+				void *event)
+{
+	struct hist_field *operand1 = hist_field->operands[0];
+	struct hist_field *operand2 = hist_field->operands[1];
+
+	u64 val1 = operand1->fn(operand1, elt, buffer, rbe, event);
+
+	return div64_u64(val1, operand2->constant);
+}
+
+static u64 div_by_mult_and_shift(struct hist_field *hist_field,
+				struct tracing_map_elt *elt,
+				struct trace_buffer *buffer,
+				struct ring_buffer_event *rbe,
+				void *event)
+{
+	struct hist_field *operand1 = hist_field->operands[0];
+	struct hist_field *operand2 = hist_field->operands[1];
+
+	u64 val1 = operand1->fn(operand1, elt, buffer, rbe, event);
+
+	/*
+	 * If the divisor is a constant, do a multiplication and shift instead.
+	 *
+	 * Choose Z = some power of 2. If Y <= Z, then:
+	 *     X / Y = (X * (Z / Y)) / Z
+	 *
+	 * (Z / Y) is a constant (mult) which is calculated at parse time, so:
+	 *     X / Y = (X * mult) / Z
+	 *
+	 * The division by Z can be replaced by a shift since Z is a power of 2:
+	 *     X / Y = (X * mult) >> HIST_DIV_SHIFT
+	 *
+	 * As long, as X < Z the results will not be off by more than 1.
+	 */
+	if (val1 < (1 << HIST_DIV_SHIFT)) {
+		u64 mult = operand2->div_multiplier;
+
+		return (val1 * mult + ((1 << HIST_DIV_SHIFT) - 1)) >> HIST_DIV_SHIFT;
+	}
+
+	return div64_u64(val1, operand2->constant);
 }
 
 static u64 hist_field_mult(struct hist_field *hist_field,
···
 	struct tracing_map_elt	*elt;
 	void			*key;
 };
+
+/*
+ * Returns the specific division function to use if the divisor
+ * is constant. This avoids extra branches when the trigger is hit.
+ */
+static hist_field_fn_t hist_field_get_div_fn(struct hist_field *divisor)
+{
+	u64 div = divisor->constant;
+
+	if (!(div & (div - 1)))
+		return div_by_power_of_two;
+
+	/* If the divisor is too large, do a regular division */
+	if (div > (1 << HIST_DIV_SHIFT))
+		return div_by_not_power_of_two;
+
+	divisor->div_multiplier = div64_u64((u64)(1 << HIST_DIV_SHIFT), div);
+	return div_by_mult_and_shift;
+}
 
 static void track_data_free(struct track_data *track_data)
 {
···
 
 	expr->operands[0] = operand1;
 	expr->operands[1] = operand2;
+
+	if (field_op == FIELD_OP_DIV &&
+			operand2_flags & HIST_FIELD_FL_CONST) {
+		u64 divisor = var2 ? var2->constant : operand2->constant;
+
+		if (!divisor) {
+			hist_err(file->tr, HIST_ERR_DIVISION_BY_ZERO, errpos(str));
+			ret = -EDOM;
+			goto free;
+		}
+
+		/*
+		 * Copy the divisor here so we don't have to look it up
+		 * later if this is a var ref
+		 */
+		operand2->constant = divisor;
+		op_fn = hist_field_get_div_fn(operand2);
+	}
 
 	if (combine_consts) {
 		if (var1)

kernel/trace/trace_osnoise.c

···
 #define CREATE_TRACE_POINTS
 #include <trace/events/osnoise.h>
 
-static struct trace_array	*osnoise_trace;
-
 /*
  * Default values.
  */
···
 
 #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_instance_registered - check if a tr is already registered
+ */
+static int osnoise_instance_registered(struct trace_array *tr)
+{
+	struct osnoise_instance *inst;
+	int found = 0;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		if (inst->tr == tr)
+			found = 1;
+	}
+	rcu_read_unlock();
+
+	return found;
+}
+
+/*
+ * 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.
···
 #endif
 };
 
-/*
- * Boolean variable used to inform that the tracer is currently sampling.
- */
-static bool osnoise_busy;
+#ifdef CONFIG_TIMERLAT_TRACER
+static inline bool timerlat_enabled(void)
+{
+	return osnoise_data.timerlat_tracer;
+}
+
+static inline int timerlat_softirq_exit(struct osnoise_variables *osn_var)
+{
+	struct timerlat_variables *tlat_var = this_cpu_tmr_var();
+	/*
+	 * If the timerlat is enabled, but the irq handler did
+	 * not run yet enabling timerlat_tracer, do not trace.
+	 */
+	if (!tlat_var->tracing_thread) {
+		osn_var->softirq.arrival_time = 0;
+		osn_var->softirq.delta_start = 0;
+		return 0;
+	}
+	return 1;
+}
+
+static inline int timerlat_thread_exit(struct osnoise_variables *osn_var)
+{
+	struct timerlat_variables *tlat_var = this_cpu_tmr_var();
+	/*
+	 * If the timerlat is enabled, but the irq handler did
+	 * not run yet enabling timerlat_tracer, do not trace.
+	 */
+	if (!tlat_var->tracing_thread) {
+		osn_var->thread.delta_start = 0;
+		osn_var->thread.arrival_time = 0;
+		return 0;
+	}
+	return 1;
+}
+#else /* CONFIG_TIMERLAT_TRACER */
+static inline bool timerlat_enabled(void)
+{
+	return false;
+}
+
+static inline int timerlat_softirq_exit(struct osnoise_variables *osn_var)
+{
+	return 1;
+}
+static inline int timerlat_thread_exit(struct osnoise_variables *osn_var)
+{
+	return 1;
+}
+#endif
 
 #ifdef CONFIG_PREEMPT_RT
 /*
···
  * 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;
···
 
 	if (!call_filter_check_discard(call, entry, buffer, event))
 		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
···
 }
 #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;
 
···
 
 	if (!call_filter_check_discard(call, entry, buffer, event))
 		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
···
 	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);
 
···
 
 	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(u64 latency)
+{
+	struct osnoise_instance *inst;
+	struct trace_buffer *buffer;
+	struct trace_stack *fstack;
+	unsigned int size;
+
+	/*
+	 * trace only if latency > print_stack config, if enabled.
+	 */
+	if (!osnoise_data.print_stack || osnoise_data.print_stack > latency)
+		return;
+
+	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
-#define timerlat_dump_stack() do {} while (0)
+#else /* CONFIG_STACKTRACE */
+#define timerlat_dump_stack(u64 latency) do {} while (0)
 #define timerlat_save_stack(a) do {} while (0)
 #endif /* CONFIG_STACKTRACE */
 #endif /* CONFIG_TIMERLAT_TRACER */
···
 	if (!osn_var->sampling)
 		return;
 
-#ifdef CONFIG_TIMERLAT_TRACER
-	/*
-	 * If the timerlat is enabled, but the irq handler did
-	 * not run yet enabling timerlat_tracer, do not trace.
-	 */
-	if (unlikely(osnoise_data.timerlat_tracer)) {
-		struct timerlat_variables *tlat_var;
-		tlat_var = this_cpu_tmr_var();
-		if (!tlat_var->tracing_thread) {
-			osn_var->softirq.arrival_time = 0;
-			osn_var->softirq.delta_start = 0;
+	if (unlikely(timerlat_enabled()))
+		if (!timerlat_softirq_exit(osn_var))
 			return;
-		}
-	}
-#endif
 
 	duration = get_int_safe_duration(osn_var, &osn_var->softirq.delta_start);
 	trace_softirq_noise(vec_nr, osn_var->softirq.arrival_time, duration);
···
 	if (!osn_var->sampling)
 		return;
 
-#ifdef CONFIG_TIMERLAT_TRACER
-	if (osnoise_data.timerlat_tracer) {
-		struct timerlat_variables *tlat_var;
-		tlat_var = this_cpu_tmr_var();
-		if (!tlat_var->tracing_thread) {
-			osn_var->thread.delta_start = 0;
-			osn_var->thread.arrival_time = 0;
+	if (unlikely(timerlat_enabled()))
+		if (!timerlat_thread_exit(osn_var))
 			return;
-		}
-	}
-#endif
 
 	duration = get_int_safe_duration(osn_var, &osn_var->thread.delta_start);
 
···
  */
 static __always_inline void osnoise_stop_tracing(void)
 {
-	struct trace_array *tr = osnoise_trace;
+	struct osnoise_instance *inst;
+	struct trace_array *tr;
 
-	trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_,
-			"stop tracing hit on cpu %d\n", smp_processor_id());
+	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);
+		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();
 }
 
 /*
···
 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;
···
 
 	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)
···
 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;
···
 	 * running, the thread needs to receive the softirq delta_start. The
 	 * reason being is that the softirq will be the last to be unfolded,
 	 * resseting the thread delay to zero.
+	 *
+	 * The PREEMPT_RT is a special case, though. As softirqs run as threads
+	 * on RT, moving the thread is enough.
 	 */
-#ifndef CONFIG_PREEMPT_RT
-	if (osn_var->softirq.delta_start) {
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) && osn_var->softirq.delta_start) {
 		copy_int_safe_time(osn_var, &osn_var->thread.delta_start,
 				   &osn_var->softirq.delta_start);
 
···
 		copy_int_safe_time(osn_var, &osn_var->thread.delta_start,
 				    &osn_var->irq.delta_start);
 	}
-#else /* CONFIG_PREEMPT_RT */
-	/*
-	 * The sofirqs run as threads on RT, so there is not need
-	 * to keep track of it.
-	 */
-	copy_int_safe_time(osn_var, &osn_var->thread.delta_start, &osn_var->irq.delta_start);
-#endif /* CONFIG_PREEMPT_RT */
 
 	/*
 	 * Compute the current time with the expected time.
···
 
 	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)
···
 
 		trace_timerlat_sample(&s);
 
-#ifdef CONFIG_STACKTRACE
-		if (osnoise_data.print_stack)
-			if (osnoise_data.print_stack <= time_to_us(diff))
-				timerlat_dump_stack();
-#endif /* CONFIG_STACKTRACE */
+		timerlat_dump_stack(time_to_us(diff));
 
 		tlat->tracing_thread = false;
 		if (osnoise_data.stop_tracing_total)
···
 	}
 
 	hrtimer_cancel(&tlat->timer);
+	return 0;
+}
+#else /* CONFIG_TIMERLAT_TRACER */
+static int timerlat_main(void *data)
+{
 	return 0;
 }
 #endif /* CONFIG_TIMERLAT_TRACER */
···
 	void *main = osnoise_main;
 	char comm[24];
 
-#ifdef CONFIG_TIMERLAT_TRACER
-	if (osnoise_data.timerlat_tracer) {
+	if (timerlat_enabled()) {
 		snprintf(comm, 24, "timerlat/%d", cpu);
 		main = timerlat_main;
 	} else {
 		snprintf(comm, 24, "osnoise/%d", cpu);
 	}
-#else
-	snprintf(comm, 24, "osnoise/%d", cpu);
-#endif
+
 	kthread = kthread_create_on_cpu(main, NULL, cpu, comm);
 
 	if (IS_ERR(kthread)) {
···
  * This starts the kernel thread that will look for osnoise on many
  * cpus.
  */
-static int start_per_cpu_kthreads(struct trace_array *tr)
+static int start_per_cpu_kthreads(void)
 {
 	struct cpumask *current_mask = &save_cpumask;
 	int retval = 0;
···
 
 	cpus_read_lock();
 	/*
-	 * Run only on CPUs in which trace and osnoise are allowed to run.
+	 * Run only on online CPUs in which osnoise is allowed to run.
 	 */
-	cpumask_and(current_mask, tr->tracing_cpumask, &osnoise_cpumask);
-	/*
-	 * And the CPU is online.
-	 */
-	cpumask_and(current_mask, cpu_online_mask, current_mask);
+	cpumask_and(current_mask, cpu_online_mask, &osnoise_cpumask);
 
 	for_each_possible_cpu(cpu)
 		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
···
 #ifdef CONFIG_HOTPLUG_CPU
 static void osnoise_hotplug_workfn(struct work_struct *dummy)
 {
-	struct trace_array *tr = osnoise_trace;
 	unsigned int cpu = smp_processor_id();
-
 
 	mutex_lock(&trace_types_lock);
 
-	if (!osnoise_busy)
+	if (!osnoise_has_registered_instances())
 		goto out_unlock_trace;
 
 	mutex_lock(&interface_lock);
 	cpus_read_lock();
 
 	if (!cpumask_test_cpu(cpu, &osnoise_cpumask))
-		goto out_unlock;
-
-	if (!cpumask_test_cpu(cpu, tr->tracing_cpumask))
 		goto out_unlock;
 
 	start_kthread(cpu);
···
 	return count;
 }
 
-static void osnoise_tracer_start(struct trace_array *tr);
-static void osnoise_tracer_stop(struct trace_array *tr);
-
 /*
  * osnoise_cpus_write - Write function for "cpus" entry
  * @filp: The active open file structure
···
  * interface to the osnoise trace. By default, it lists all  CPUs,
  * in this way, allowing osnoise threads to run on any online CPU
  * of the system. It serves to restrict the execution of osnoise to the
- * set of CPUs writing via this interface. Note that osnoise also
- * respects the "tracing_cpumask." Hence, osnoise threads will run only
- * on the set of CPUs allowed here AND on "tracing_cpumask." Why not
- * have just "tracing_cpumask?" Because the user might be interested
- * in tracing what is running on other CPUs. For instance, one might
- * run osnoise in one HT CPU while observing what is running on the
- * sibling HT CPU.
+ * set of CPUs writing via this interface. Why not use "tracing_cpumask"?
+ * Because the user might be interested in tracing what is running on
+ * other CPUs. For instance, one might run osnoise in one HT CPU
+ * while observing what is running on the sibling HT CPU.
  */
 static ssize_t
 osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 		   loff_t *ppos)
 {
-	struct trace_array *tr = osnoise_trace;
 	cpumask_var_t osnoise_cpumask_new;
 	int running, err;
 	char buf[256];
···
 		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)
-		osnoise_tracer_stop(tr);
+		stop_per_cpu_kthreads();
 
 	mutex_lock(&interface_lock);
 	/*
···
 	mutex_unlock(&interface_lock);
 
 	if (running)
-		osnoise_tracer_start(tr);
+		start_per_cpu_kthreads();
 	mutex_unlock(&trace_types_lock);
 
 	free_cpumask_var(osnoise_cpumask_new);
···
 	.llseek		= generic_file_llseek,
 };
 
+#ifdef CONFIG_TIMERLAT_TRACER
+#ifdef CONFIG_STACKTRACE
+static int init_timerlat_stack_tracefs(struct dentry *top_dir)
+{
+	struct dentry *tmp;
+
+	tmp = tracefs_create_file("print_stack", TRACE_MODE_WRITE, top_dir,
+				  &osnoise_print_stack, &trace_min_max_fops);
+	if (!tmp)
+		return -ENOMEM;
+
+	return 0;
+}
+#else /* CONFIG_STACKTRACE */
+static int init_timerlat_stack_tracefs(struct dentry *top_dir)
+{
+	return 0;
+}
+#endif /* CONFIG_STACKTRACE */
+
+/*
+ * init_timerlat_tracefs - A function to initialize the timerlat interface files
+ */
+static int init_timerlat_tracefs(struct dentry *top_dir)
+{
+	struct dentry *tmp;
+
+	tmp = tracefs_create_file("timerlat_period_us", TRACE_MODE_WRITE, top_dir,
+				  &timerlat_period, &trace_min_max_fops);
+	if (!tmp)
+		return -ENOMEM;
+
+	return init_timerlat_stack_tracefs(top_dir);
+}
+#else /* CONFIG_TIMERLAT_TRACER */
+static int init_timerlat_tracefs(struct dentry *top_dir)
+{
+	return 0;
+}
+#endif /* CONFIG_TIMERLAT_TRACER */
+
 /*
  * init_tracefs - A function to initialize the tracefs interface files
  *
···
 	tmp = trace_create_file("cpus", TRACE_MODE_WRITE, top_dir, NULL, &cpus_fops);
 	if (!tmp)
 		goto err;
-#ifdef CONFIG_TIMERLAT_TRACER
-#ifdef CONFIG_STACKTRACE
-	tmp = tracefs_create_file("print_stack", TRACE_MODE_WRITE, top_dir,
-				  &osnoise_print_stack, &trace_min_max_fops);
-	if (!tmp)
-		goto err;
-#endif
 
-	tmp = tracefs_create_file("timerlat_period_us", TRACE_MODE_WRITE, top_dir,
-				  &timerlat_period, &trace_min_max_fops);
-	if (!tmp)
+	ret = init_timerlat_tracefs(top_dir);
+	if (ret)
 		goto err;
-#endif
 
 	return 0;
 
···
 	return -EINVAL;
 }
 
-static int __osnoise_tracer_start(struct trace_array *tr)
+/*
+ * osnoise_workload_start - start the workload and hook to events
+ */
+static int osnoise_workload_start(void)
 {
 	int retval;
+
+	/*
+	 * Instances need to be registered after calling workload
+	 * start. Hence, if there is already an instance, the
+	 * workload was already registered. Otherwise, this
+	 * code is on the way to register the first instance,
+	 * and the workload will start.
+	 */
+	if (osnoise_has_registered_instances())
+		return 0;
 
 	osn_var_reset_all();
 
 	retval = osnoise_hook_events();
 	if (retval)
 		return retval;
+
 	/*
-	 * Make sure NMIs see reseted values.
+	 * Make sure that ftrace_nmi_enter/exit() see reset values
+	 * before enabling trace_osnoise_callback_enabled.
 	 */
 	barrier();
 	trace_osnoise_callback_enabled = true;
 
-	retval = start_per_cpu_kthreads(tr);
+	retval = start_per_cpu_kthreads();
 	if (retval) {
 		unhook_irq_events();
 		return retval;
 	}
 
-	osnoise_busy = true;
-
 	return 0;
 }
 
-static void osnoise_tracer_start(struct trace_array *tr)
+/*
+ * osnoise_workload_stop - stop the workload and unhook the events
+ */
+static void osnoise_workload_stop(void)
 {
-	int retval;
-
-	if (osnoise_busy)
-		return;
-
-	retval = __osnoise_tracer_start(tr);
-	if (retval)
-		pr_err(BANNER "Error starting osnoise tracer\n");
-
-}
-
-static void osnoise_tracer_stop(struct trace_array *tr)
-{
-	if (!osnoise_busy)
+	/*
+	 * Instances need to be unregistered before calling
+	 * stop. Hence, if there is a registered instance, more
+	 * than one instance is running, and the workload will not
+	 * yet stop. Otherwise, this code is on the way to disable
+	 * the last instance, and the workload can stop.
+	 */
+	if (osnoise_has_registered_instances())
 		return;
 
 	trace_osnoise_callback_enabled = false;
+	/*
+	 * Make sure that ftrace_nmi_enter/exit() see
+	 * trace_osnoise_callback_enabled as false before continuing.
+	 */
 	barrier();
 
 	stop_per_cpu_kthreads();
···
 	unhook_irq_events();
 	unhook_softirq_events();
 	unhook_thread_events();
+}
 
-	osnoise_busy = false;
+static void osnoise_tracer_start(struct trace_array *tr)
+{
+	int retval;
+
+	/*
+	 * If the instance is already registered, there is no need to
+	 * register it again.
+	 */
+	if (osnoise_instance_registered(tr))
+		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)
+{
+	osnoise_unregister_instance(tr);
+	osnoise_workload_stop();
 }
 
 static int osnoise_tracer_init(struct trace_array *tr)
 {
-
-	/* Only allow one instance to enable this */
-	if (osnoise_busy)
+	/*
+	 * Only allow osnoise tracer if timerlat tracer is not running
+	 * already.
+	 */
+	if (timerlat_enabled())
 		return -EBUSY;
 
-	osnoise_trace = tr;
 	tr->max_latency = 0;
 
 	osnoise_tracer_start(tr);
-
 	return 0;
 }
 
···
 {
 	int retval;
 
-	if (osnoise_busy)
+	/*
+	 * If the instance is already registered, there is no need to
+	 * register it again.
+	 */
+	if (osnoise_instance_registered(tr))
 		return;
 
-	osnoise_data.timerlat_tracer = 1;
-
-	retval = __osnoise_tracer_start(tr);
+	retval = osnoise_workload_start();
 	if (retval)
-		goto out_err;
+		pr_err(BANNER "Error starting timerlat tracer\n");
+
+	osnoise_register_instance(tr);
 
 	return;
-out_err:
-	pr_err(BANNER "Error starting timerlat tracer\n");
 }
 
 static void timerlat_tracer_stop(struct trace_array *tr)
 {
 	int cpu;
 
-	if (!osnoise_busy)
-		return;
+	osnoise_unregister_instance(tr);
 
-	for_each_online_cpu(cpu)
-		per_cpu(per_cpu_osnoise_var, cpu).sampling = 0;
+	/*
+	 * Instruct the threads to stop only if this is the last instance.
+	 */
+	if (!osnoise_has_registered_instances()) {
+		for_each_online_cpu(cpu)
+			per_cpu(per_cpu_osnoise_var, cpu).sampling = 0;
+	}
 
-	osnoise_tracer_stop(tr);
-
-	osnoise_data.timerlat_tracer = 0;
+	osnoise_workload_stop();
 }
 
 static int timerlat_tracer_init(struct trace_array *tr)
 {
-	/* Only allow one instance to enable this */
-	if (osnoise_busy)
+	/*
+	 * Only allow timerlat tracer if osnoise tracer is not running already.
+	 */
+	if (osnoise_has_registered_instances() && !osnoise_data.timerlat_tracer)
 		return -EBUSY;
 
-	osnoise_trace = tr;
+	/*
+	 * If this is the first instance, set timerlat_tracer to block
+	 * osnoise tracer start.
+	 */
+	if (!osnoise_has_registered_instances())
+		osnoise_data.timerlat_tracer = 1;
 
 	tr->max_latency = 0;
-
 	timerlat_tracer_start(tr);
 
 	return 0;
···
 static void timerlat_tracer_reset(struct trace_array *tr)
 {
 	timerlat_tracer_stop(tr);
+
+	/*
+	 * If this is the last instance, reset timerlat_tracer allowing
+	 * osnoise to be started.
+	 */
+	if (!osnoise_has_registered_instances())
+		osnoise_data.timerlat_tracer = 0;
 }
 
 static struct tracer timerlat_tracer __read_mostly = {
···
 	.print_header	= print_timerlat_headers,
 	.allow_instances = true,
 };
+
+__init static int init_timerlat_tracer(void)
+{
+	return register_tracer(&timerlat_tracer);
+}
+#else /* CONFIG_TIMERLAT_TRACER */
+__init static int init_timerlat_tracer(void)
+{
+	return 0;
+}
 #endif /* CONFIG_TIMERLAT_TRACER */
 
 __init static int init_osnoise_tracer(void)
···
 		return ret;
 	}
 
-#ifdef CONFIG_TIMERLAT_TRACER
-	ret = register_tracer(&timerlat_tracer);
+	ret = init_timerlat_tracer();
 	if (ret) {
-		pr_err(BANNER "Error registering timerlat\n");
+		pr_err(BANNER "Error registering timerlat!\n");
 		return ret;
 	}
-#endif
+
 	osnoise_init_hotplug_support();
+
+	INIT_LIST_HEAD_RCU(&osnoise_instances);
 
 	init_tracefs();
 

samples/ftrace/ftrace-direct-multi.c

···
 #include <linux/ftrace.h>
 #include <linux/sched/stat.h>
 
+extern void my_direct_func(unsigned long ip);
+
 void my_direct_func(unsigned long ip)
 {
 	trace_printk("ip %lx\n", ip);

tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-expressions.tc

···
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: event trigger - test histogram expression parsing
+# requires: set_event events/sched/sched_process_fork/trigger events/sched/sched_process_fork/hist error_log "<var1>=<field|var_ref|numeric_literal>":README
+
+
+fail() { #msg
+    echo $1
+    exit_fail
+}
+
+test_hist_expr() { # test_name expression expected_val
+    trigger="events/sched/sched_process_fork/trigger"
+
+    reset_trigger_file $trigger
+
+    echo "Test hist trigger expressions - $1"
+
+    echo "hist:keys=common_pid:x=$2" > $trigger
+
+    for i in `seq 1 10` ; do ( echo "forked" > /dev/null); done
+
+    actual=`grep -o 'x=[[:digit:]]*' $trigger | awk -F= '{ print $2 }'`
+
+    if [ $actual != $3 ]; then
+        fail "Failed hist trigger expression evaluation: Expression: $2 Expected: $3, Actual: $actual"
+    fi
+
+    reset_trigger_file $trigger
+}
+
+check_error() { # test_name command-with-error-pos-by-^
+    trigger="events/sched/sched_process_fork/trigger"
+
+    echo "Test hist trigger expressions - $1"
+    ftrace_errlog_check 'hist:sched:sched_process_fork' "$2" $trigger
+}
+
+test_hist_expr "Variable assignment" "123" "123"
+
+test_hist_expr "Subtraction not associative" "16-8-4-2" "2"
+
+test_hist_expr "Division not associative" "64/8/4/2" "1"
+
+test_hist_expr "Same precedence operators (+,-) evaluated left to right" "16-8+4+2" "14"
+
+test_hist_expr "Same precedence operators (*,/) evaluated left to right" "4*3/2*2" "12"
+
+test_hist_expr "Multiplication evaluated before addition/subtraction" "4+3*2-2" "8"
+
+test_hist_expr "Division evaluated before addition/subtraction" "4+6/2-2" "5"
+
+# err pos for "too many subexpressions" is dependent on where
+# the last subexpression was detected. This can vary depending
+# on how the expression tree was generated.
+check_error "Too many subexpressions" 'hist:keys=common_pid:x=32+^10*3/20-4'
+check_error "Too many subexpressions" 'hist:keys=common_pid:x=^1+2+3+4+5'
+
+check_error "Unary minus not supported in subexpression" 'hist:keys=common_pid:x=-(^1)+2'
+
+check_error "Division by zero" 'hist:keys=common_pid:x=3/^0'
+
+exit 0