Merge tag 'trace-v6.5' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing updates from Steven Rostedt:

 - Add new feature to have function graph tracer record the return
   value. Adds a new option: funcgraph-retval ; when set, will show the
   return value of a function in the function graph tracer.

 - Also add the option: funcgraph-retval-hex where if it is not set, and
   the return value is an error code, then it will return the decimal of
   the error code, otherwise it still reports the hex value.

 - Add the file /sys/kernel/tracing/osnoise/per_cpu/cpu<cpu>/timerlat_fd
   That when a application opens it, it becomes the task that the timer
   lat tracer traces. The application can also read this file to find
   out how it's being interrupted.

 - Add the file /sys/kernel/tracing/available_filter_functions_addrs
   that works just the same as available_filter_functions but also shows
   the addresses of the functions like kallsyms, except that it gives
   the address of where the fentry/mcount jump/nop is. This is used by
   BPF to make it easier to attach BPF programs to ftrace hooks.

 - Replace strlcpy with strscpy in the tracing boot code.

* tag 'trace-v6.5' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  tracing: Fix warnings when building htmldocs for function graph retval
  riscv: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL
  tracing/boot: Replace strlcpy with strscpy
  tracing/timerlat: Add user-space interface
  tracing/osnoise: Skip running osnoise if all instances are off
  tracing/osnoise: Switch from PF_NO_SETAFFINITY to migrate_disable
  ftrace: Show all functions with addresses in available_filter_functions_addrs
  selftests/ftrace: Add funcgraph-retval test case
  LoongArch: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL
  x86/ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL
  arm64: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL
  tracing: Add documentation for funcgraph-retval and funcgraph-retval-hex
  function_graph: Support recording and printing the return value of function
  fgraph: Add declaration of "struct fgraph_ret_regs"

9 files changed, 665 insertions, 23 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 8cf97fa4a4b3..abe5c583bd59 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -31,6 +31,9 @@ config HAVE_FUNCTION_GRAPH_TRACER
 	help
 	  See Documentation/trace/ftrace-design.rst
 
+config HAVE_FUNCTION_GRAPH_RETVAL
+	bool
+
 config HAVE_DYNAMIC_FTRACE
 	bool
 	help
@@ -227,6 +230,18 @@ config FUNCTION_GRAPH_TRACER
 	  the return value. This is done by setting the current return
 	  address on the current task structure into a stack of calls.
 
+config FUNCTION_GRAPH_RETVAL
+	bool "Kernel Function Graph Return Value"
+	depends on HAVE_FUNCTION_GRAPH_RETVAL
+	depends on FUNCTION_GRAPH_TRACER
+	default n
+	help
+	  Support recording and printing the function return value when
+	  using function graph tracer. It can be helpful to locate functions
+	  that return errors. This feature is off by default, and you can
+	  enable it via the trace option funcgraph-retval.
+	  See Documentation/trace/ftrace.rst
+
 config DYNAMIC_FTRACE
 	bool "enable/disable function tracing dynamically"
 	depends on FUNCTION_TRACER
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 218cd95bf8e4..cd2c35b1dd8f 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -236,16 +236,23 @@ static struct notifier_block ftrace_suspend_notifier = {
 	.notifier_call = ftrace_suspend_notifier_call,
 };
 
+/* fgraph_ret_regs is not defined without CONFIG_FUNCTION_GRAPH_RETVAL */
+struct fgraph_ret_regs;
+
 /*
  * Send the trace to the ring-buffer.
  * @return the original return address.
  */
-unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
+static unsigned long __ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs,
+						unsigned long frame_pointer)
 {
 	struct ftrace_graph_ret trace;
 	unsigned long ret;
 
 	ftrace_pop_return_trace(&trace, &ret, frame_pointer);
+#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
+	trace.retval = fgraph_ret_regs_return_value(ret_regs);
+#endif
 	trace.rettime = trace_clock_local();
 	ftrace_graph_return(&trace);
 	/*
@@ -266,6 +273,23 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
 	return ret;
 }
 
+/*
+ * After all architecures have selected HAVE_FUNCTION_GRAPH_RETVAL, we can
+ * leave only ftrace_return_to_handler(ret_regs).
+ */
+#ifdef CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
+unsigned long ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs)
+{
+	return __ftrace_return_to_handler(ret_regs,
+				fgraph_ret_regs_frame_pointer(ret_regs));
+}
+#else
+unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
+{
+	return __ftrace_return_to_handler(NULL, frame_pointer);
+}
+#endif
+
 /**
  * ftrace_graph_get_ret_stack - return the entry of the shadow stack
  * @task: The task to read the shadow stack from
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 6a77edb51f18..3740aca79fe7 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3861,6 +3861,9 @@ static int t_show(struct seq_file *m, void *v)
 	if (!rec)
 		return 0;
 
+	if (iter->flags & FTRACE_ITER_ADDRS)
+		seq_printf(m, "%lx ", rec->ip);
+
 	if (print_rec(m, rec->ip)) {
 		/* This should only happen when a rec is disabled */
 		WARN_ON_ONCE(!(rec->flags & FTRACE_FL_DISABLED));
@@ -3996,6 +3999,30 @@ ftrace_touched_open(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static int
+ftrace_avail_addrs_open(struct inode *inode, struct file *file)
+{
+	struct ftrace_iterator *iter;
+	int ret;
+
+	ret = security_locked_down(LOCKDOWN_TRACEFS);
+	if (ret)
+		return ret;
+
+	if (unlikely(ftrace_disabled))
+		return -ENODEV;
+
+	iter = __seq_open_private(file, &show_ftrace_seq_ops, sizeof(*iter));
+	if (!iter)
+		return -ENOMEM;
+
+	iter->pg = ftrace_pages_start;
+	iter->flags = FTRACE_ITER_ADDRS;
+	iter->ops = &global_ops;
+
+	return 0;
+}
+
 /**
  * ftrace_regex_open - initialize function tracer filter files
  * @ops: The ftrace_ops that hold the hash filters
@@ -5916,6 +5943,13 @@ static const struct file_operations ftrace_touched_fops = {
 	.release = seq_release_private,
 };
 
+static const struct file_operations ftrace_avail_addrs_fops = {
+	.open = ftrace_avail_addrs_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release_private,
+};
+
 static const struct file_operations ftrace_filter_fops = {
 	.open = ftrace_filter_open,
 	.read = seq_read,
@@ -6377,6 +6411,9 @@ static __init int ftrace_init_dyn_tracefs(struct dentry *d_tracer)
 	trace_create_file("available_filter_functions", TRACE_MODE_READ,
 			d_tracer, NULL, &ftrace_avail_fops);
 
+	trace_create_file("available_filter_functions_addrs", TRACE_MODE_READ,
+			d_tracer, NULL, &ftrace_avail_addrs_fops);
+
 	trace_create_file("enabled_functions", TRACE_MODE_READ,
 			d_tracer, NULL, &ftrace_enabled_fops);
 
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 79bdefe9261b..e6407a27d644 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -832,6 +832,8 @@ static __always_inline bool ftrace_hash_empty(struct ftrace_hash *hash)
 #define TRACE_GRAPH_PRINT_TAIL          0x100
 #define TRACE_GRAPH_SLEEP_TIME          0x200
 #define TRACE_GRAPH_GRAPH_TIME          0x400
+#define TRACE_GRAPH_PRINT_RETVAL        0x800
+#define TRACE_GRAPH_PRINT_RETVAL_HEX    0x1000
 #define TRACE_GRAPH_PRINT_FILL_SHIFT	28
 #define TRACE_GRAPH_PRINT_FILL_MASK	(0x3 << TRACE_GRAPH_PRINT_FILL_SHIFT)
 
diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index 778200dd8ede..5fe525f1b8cc 100644
--- a/kernel/trace/trace_boot.c
+++ b/kernel/trace/trace_boot.c
@@ -31,7 +31,7 @@ trace_boot_set_instance_options(struct trace_array *tr, struct xbc_node *node)
 
 	/* Common ftrace options */
 	xbc_node_for_each_array_value(node, "options", anode, p) {
-		if (strlcpy(buf, p, ARRAY_SIZE(buf)) >= ARRAY_SIZE(buf)) {
+		if (strscpy(buf, p, ARRAY_SIZE(buf)) == -E2BIG) {
 			pr_err("String is too long: %s\n", p);
 			continue;
 		}
@@ -87,7 +87,7 @@ trace_boot_enable_events(struct trace_array *tr, struct xbc_node *node)
 	const char *p;
 
 	xbc_node_for_each_array_value(node, "events", anode, p) {
-		if (strlcpy(buf, p, ARRAY_SIZE(buf)) >= ARRAY_SIZE(buf)) {
+		if (strscpy(buf, p, ARRAY_SIZE(buf)) == -E2BIG) {
 			pr_err("String is too long: %s\n", p);
 			continue;
 		}
@@ -486,7 +486,7 @@ trace_boot_init_one_event(struct trace_array *tr, struct xbc_node *gnode,
 
 	p = xbc_node_find_value(enode, "filter", NULL);
 	if (p && *p != '\0') {
-		if (strlcpy(buf, p, ARRAY_SIZE(buf)) >= ARRAY_SIZE(buf))
+		if (strscpy(buf, p, ARRAY_SIZE(buf)) == -E2BIG)
 			pr_err("filter string is too long: %s\n", p);
 		else if (apply_event_filter(file, buf) < 0)
 			pr_err("Failed to apply filter: %s\n", buf);
@@ -494,7 +494,7 @@ trace_boot_init_one_event(struct trace_array *tr, struct xbc_node *gnode,
 
 	if (IS_ENABLED(CONFIG_HIST_TRIGGERS)) {
 		xbc_node_for_each_array_value(enode, "actions", anode, p) {
-			if (strlcpy(buf, p, ARRAY_SIZE(buf)) >= ARRAY_SIZE(buf))
+			if (strscpy(buf, p, ARRAY_SIZE(buf)) == -E2BIG)
 				pr_err("action string is too long: %s\n", p);
 			else if (trigger_process_regex(file, buf) < 0)
 				pr_err("Failed to apply an action: %s\n", p);
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index cd41e863b51c..340b2fa98218 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -86,6 +86,30 @@ FTRACE_ENTRY_PACKED(funcgraph_entry, ftrace_graph_ent_entry,
 );
 
 /* Function return entry */
+#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
+
+FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
+
+	TRACE_GRAPH_RET,
+
+	F_STRUCT(
+		__field_struct(	struct ftrace_graph_ret,	ret	)
+		__field_packed(	unsigned long,	ret,		func	)
+		__field_packed(	unsigned long,	ret,		retval	)
+		__field_packed(	int,		ret,		depth	)
+		__field_packed(	unsigned int,	ret,		overrun	)
+		__field_packed(	unsigned long long, ret,	calltime)
+		__field_packed(	unsigned long long, ret,	rettime	)
+	),
+
+	F_printk("<-- %ps (%d) (start: %llx  end: %llx) over: %d retval: %lx",
+		 (void *)__entry->func, __entry->depth,
+		 __entry->calltime, __entry->rettime,
+		 __entry->depth, __entry->retval)
+);
+
+#else
+
 FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
 
 	TRACE_GRAPH_RET,
@@ -105,6 +129,8 @@ FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
 		 __entry->depth)
 );
 
+#endif
+
 /*
  * Context switch trace entry - which task (and prio) we switched from/to:
  *
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 203204cadf92..c35fbaab2a47 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -58,6 +58,12 @@ static struct tracer_opt trace_opts[] = {
 	{ TRACER_OPT(funcgraph-irqs, TRACE_GRAPH_PRINT_IRQS) },
 	/* Display function name after trailing } */
 	{ TRACER_OPT(funcgraph-tail, TRACE_GRAPH_PRINT_TAIL) },
+#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
+	/* Display function return value ? */
+	{ TRACER_OPT(funcgraph-retval, TRACE_GRAPH_PRINT_RETVAL) },
+	/* Display function return value in hexadecimal format ? */
+	{ TRACER_OPT(funcgraph-retval-hex, TRACE_GRAPH_PRINT_RETVAL_HEX) },
+#endif
 	/* Include sleep time (scheduled out) between entry and return */
 	{ TRACER_OPT(sleep-time, TRACE_GRAPH_SLEEP_TIME) },
 
@@ -619,6 +625,56 @@ print_graph_duration(struct trace_array *tr, unsigned long long duration,
 	trace_seq_puts(s, "|  ");
 }
 
+#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
+
+#define __TRACE_GRAPH_PRINT_RETVAL TRACE_GRAPH_PRINT_RETVAL
+
+static void print_graph_retval(struct trace_seq *s, unsigned long retval,
+				bool leaf, void *func, bool hex_format)
+{
+	unsigned long err_code = 0;
+
+	if (retval == 0 || hex_format)
+		goto done;
+
+	/* Check if the return value matches the negative format */
+	if (IS_ENABLED(CONFIG_64BIT) && (retval & BIT(31)) &&
+		(((u64)retval) >> 32) == 0) {
+		/* sign extension */
+		err_code = (unsigned long)(s32)retval;
+	} else {
+		err_code = retval;
+	}
+
+	if (!IS_ERR_VALUE(err_code))
+		err_code = 0;
+
+done:
+	if (leaf) {
+		if (hex_format || (err_code == 0))
+			trace_seq_printf(s, "%ps(); /* = 0x%lx */\n",
+					func, retval);
+		else
+			trace_seq_printf(s, "%ps(); /* = %ld */\n",
+					func, err_code);
+	} else {
+		if (hex_format || (err_code == 0))
+			trace_seq_printf(s, "} /* %ps = 0x%lx */\n",
+					func, retval);
+		else
+			trace_seq_printf(s, "} /* %ps = %ld */\n",
+					func, err_code);
+	}
+}
+
+#else
+
+#define __TRACE_GRAPH_PRINT_RETVAL 0
+
+#define print_graph_retval(_seq, _retval, _leaf, _func, _format) do {} while (0)
+
+#endif
+
 /* Case of a leaf function on its call entry */
 static enum print_line_t
 print_graph_entry_leaf(struct trace_iterator *iter,
@@ -663,7 +719,15 @@ print_graph_entry_leaf(struct trace_iterator *iter,
 	for (i = 0; i < call->depth * TRACE_GRAPH_INDENT; i++)
 		trace_seq_putc(s, ' ');
 
-	trace_seq_printf(s, "%ps();\n", (void *)call->func);
+	/*
+	 * Write out the function return value if the option function-retval is
+	 * enabled.
+	 */
+	if (flags & __TRACE_GRAPH_PRINT_RETVAL)
+		print_graph_retval(s, graph_ret->retval, true, (void *)call->func,
+				!!(flags & TRACE_GRAPH_PRINT_RETVAL_HEX));
+	else
+		trace_seq_printf(s, "%ps();\n", (void *)call->func);
 
 	print_graph_irq(iter, graph_ret->func, TRACE_GRAPH_RET,
 			cpu, iter->ent->pid, flags);
@@ -942,16 +1006,25 @@ print_graph_return(struct ftrace_graph_ret *trace, struct trace_seq *s,
 		trace_seq_putc(s, ' ');
 
 	/*
-	 * If the return function does not have a matching entry,
-	 * then the entry was lost. Instead of just printing
-	 * the '}' and letting the user guess what function this
-	 * belongs to, write out the function name. Always do
-	 * that if the funcgraph-tail option is enabled.
+	 * Always write out the function name and its return value if the
+	 * function-retval option is enabled.
 	 */
-	if (func_match && !(flags & TRACE_GRAPH_PRINT_TAIL))
-		trace_seq_puts(s, "}\n");
-	else
-		trace_seq_printf(s, "} /* %ps */\n", (void *)trace->func);
+	if (flags & __TRACE_GRAPH_PRINT_RETVAL) {
+		print_graph_retval(s, trace->retval, false, (void *)trace->func,
+			!!(flags & TRACE_GRAPH_PRINT_RETVAL_HEX));
+	} else {
+		/*
+		 * If the return function does not have a matching entry,
+		 * then the entry was lost. Instead of just printing
+		 * the '}' and letting the user guess what function this
+		 * belongs to, write out the function name. Always do
+		 * that if the funcgraph-tail option is enabled.
+		 */
+		if (func_match && !(flags & TRACE_GRAPH_PRINT_TAIL))
+			trace_seq_puts(s, "}\n");
+		else
+			trace_seq_printf(s, "} /* %ps */\n", (void *)trace->func);
+	}
 
 	/* Overrun */
 	if (flags & TRACE_GRAPH_PRINT_OVERRUN)
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index e97e3fa5cbed..bd0d01d00fb9 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -181,6 +181,7 @@ struct osn_irq {
 
 #define IRQ_CONTEXT	0
 #define THREAD_CONTEXT	1
+#define THREAD_URET	2
 /*
  * sofirq runtime info.
  */
@@ -238,6 +239,7 @@ struct timerlat_variables {
 	u64			abs_period;
 	bool			tracing_thread;
 	u64			count;
+	bool			uthread_migrate;
 };
 
 static DEFINE_PER_CPU(struct timerlat_variables, per_cpu_timerlat_var);
@@ -1181,6 +1183,78 @@ thread_exit(struct osnoise_variables *osn_var, struct task_struct *t)
 	osn_var->thread.arrival_time = 0;
 }
 
+#ifdef CONFIG_TIMERLAT_TRACER
+/*
+ * osnoise_stop_exception - Stop tracing and the tracer.
+ */
+static __always_inline void osnoise_stop_exception(char *msg, int cpu)
+{
+	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 due to exception: %s\n",
+				       smp_processor_id(),
+				       msg);
+
+		if (test_bit(OSN_PANIC_ON_STOP, &osnoise_options))
+			panic("tracer hit on cpu %d due to exception: %s\n",
+			      smp_processor_id(),
+			      msg);
+
+		tracer_tracing_off(tr);
+	}
+	rcu_read_unlock();
+}
+
+/*
+ * trace_sched_migrate_callback - sched:sched_migrate_task trace event handler
+ *
+ * his function is hooked to the sched:sched_migrate_task trace event, and monitors
+ * timerlat user-space thread migration.
+ */
+static void trace_sched_migrate_callback(void *data, struct task_struct *p, int dest_cpu)
+{
+	struct osnoise_variables *osn_var;
+	long cpu = task_cpu(p);
+
+	osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu);
+	if (osn_var->pid == p->pid && dest_cpu != cpu) {
+		per_cpu_ptr(&per_cpu_timerlat_var, cpu)->uthread_migrate = 1;
+		osnoise_taint("timerlat user-thread migrated\n");
+		osnoise_stop_exception("timerlat user-thread migrated", cpu);
+	}
+}
+
+static int register_migration_monitor(void)
+{
+	int ret = 0;
+
+	/*
+	 * Timerlat thread migration check is only required when running timerlat in user-space.
+	 * Thus, enable callback only if timerlat is set with no workload.
+	 */
+	if (timerlat_enabled() && !test_bit(OSN_WORKLOAD, &osnoise_options))
+		ret = register_trace_sched_migrate_task(trace_sched_migrate_callback, NULL);
+
+	return ret;
+}
+
+static void unregister_migration_monitor(void)
+{
+	if (timerlat_enabled() && !test_bit(OSN_WORKLOAD, &osnoise_options))
+		unregister_trace_sched_migrate_task(trace_sched_migrate_callback, NULL);
+}
+#else
+static int register_migration_monitor(void)
+{
+	return 0;
+}
+static void unregister_migration_monitor(void) {}
+#endif
 /*
  * trace_sched_switch - sched:sched_switch trace event handler
  *
@@ -1204,7 +1278,7 @@ trace_sched_switch_callback(void *data, bool preempt,
 }
 
 /*
- * hook_thread_events - Hook the insturmentation for thread noise
+ * hook_thread_events - Hook the instrumentation for thread noise
  *
  * Hook the osnoise tracer callbacks to handle the noise from other
  * threads on the necessary kernel events.
@@ -1217,11 +1291,19 @@ static int hook_thread_events(void)
 	if (ret)
 		return -EINVAL;
 
+	ret = register_migration_monitor();
+	if (ret)
+		goto out_unreg;
+
 	return 0;
+
+out_unreg:
+	unregister_trace_sched_switch(trace_sched_switch_callback, NULL);
+	return -EINVAL;
 }
 
 /*
- * unhook_thread_events - *nhook the insturmentation for thread noise
+ * unhook_thread_events - unhook the instrumentation for thread noise
  *
  * Unook the osnoise tracer callbacks to handle the noise from other
  * threads on the necessary kernel events.
@@ -1229,6 +1311,7 @@ static int hook_thread_events(void)
 static void unhook_thread_events(void)
 {
 	unregister_trace_sched_switch(trace_sched_switch_callback, NULL);
+	unregister_migration_monitor();
 }
 
 /*
@@ -1286,6 +1369,22 @@ static __always_inline void osnoise_stop_tracing(void)
 }
 
 /*
+ * osnoise_has_tracing_on - Check if there is at least one instance on
+ */
+static __always_inline int osnoise_has_tracing_on(void)
+{
+	struct osnoise_instance *inst;
+	int trace_is_on = 0;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list)
+		trace_is_on += tracer_tracing_is_on(inst->tr);
+	rcu_read_unlock();
+
+	return trace_is_on;
+}
+
+/*
  * notify_new_max_latency - Notify a new max latency via fsnotify interface.
  */
 static void notify_new_max_latency(u64 latency)
@@ -1517,13 +1616,16 @@ static struct cpumask save_cpumask;
 /*
  * osnoise_sleep - sleep until the next period
  */
-static void osnoise_sleep(void)
+static void osnoise_sleep(bool skip_period)
 {
 	u64 interval;
 	ktime_t wake_time;
 
 	mutex_lock(&interface_lock);
-	interval = osnoise_data.sample_period - osnoise_data.sample_runtime;
+	if (skip_period)
+		interval = osnoise_data.sample_period;
+	else
+		interval = osnoise_data.sample_period - osnoise_data.sample_runtime;
 	mutex_unlock(&interface_lock);
 
 	/*
@@ -1546,6 +1648,39 @@ static void osnoise_sleep(void)
 }
 
 /*
+ * osnoise_migration_pending - checks if the task needs to migrate
+ *
+ * osnoise/timerlat threads are per-cpu. If there is a pending request to
+ * migrate the thread away from the current CPU, something bad has happened.
+ * Play the good citizen and leave.
+ *
+ * Returns 0 if it is safe to continue, 1 otherwise.
+ */
+static inline int osnoise_migration_pending(void)
+{
+	if (!current->migration_pending)
+		return 0;
+
+	/*
+	 * If migration is pending, there is a task waiting for the
+	 * tracer to enable migration. The tracer does not allow migration,
+	 * thus: taint and leave to unblock the blocked thread.
+	 */
+	osnoise_taint("migration requested to osnoise threads, leaving.");
+
+	/*
+	 * Unset this thread from the threads managed by the interface.
+	 * The tracers are responsible for cleaning their env before
+	 * exiting.
+	 */
+	mutex_lock(&interface_lock);
+	this_cpu_osn_var()->kthread = NULL;
+	mutex_unlock(&interface_lock);
+
+	return 1;
+}
+
+/*
  * osnoise_main - The osnoise detection kernel thread
  *
  * Calls run_osnoise() function to measure the osnoise for the configured runtime,
@@ -1553,12 +1688,35 @@ static void osnoise_sleep(void)
  */
 static int osnoise_main(void *data)
 {
+	unsigned long flags;
+
+	/*
+	 * This thread was created pinned to the CPU using PF_NO_SETAFFINITY.
+	 * The problem is that cgroup does not allow PF_NO_SETAFFINITY thread.
+	 *
+	 * To work around this limitation, disable migration and remove the
+	 * flag.
+	 */
+	migrate_disable();
+	raw_spin_lock_irqsave(&current->pi_lock, flags);
+	current->flags &= ~(PF_NO_SETAFFINITY);
+	raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 
 	while (!kthread_should_stop()) {
+		if (osnoise_migration_pending())
+			break;
+
+		/* skip a period if tracing is off on all instances */
+		if (!osnoise_has_tracing_on()) {
+			osnoise_sleep(true);
+			continue;
+		}
+
 		run_osnoise();
-		osnoise_sleep();
+		osnoise_sleep(false);
 	}
 
+	migrate_enable();
 	return 0;
 }
 
@@ -1706,6 +1864,7 @@ static int timerlat_main(void *data)
 	struct timerlat_variables *tlat = this_cpu_tmr_var();
 	struct timerlat_sample s;
 	struct sched_param sp;
+	unsigned long flags;
 	u64 now, diff;
 
 	/*
@@ -1714,6 +1873,18 @@ static int timerlat_main(void *data)
 	sp.sched_priority = DEFAULT_TIMERLAT_PRIO;
 	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
 
+	/*
+	 * This thread was created pinned to the CPU using PF_NO_SETAFFINITY.
+	 * The problem is that cgroup does not allow PF_NO_SETAFFINITY thread.
+	 *
+	 * To work around this limitation, disable migration and remove the
+	 * flag.
+	 */
+	migrate_disable();
+	raw_spin_lock_irqsave(&current->pi_lock, flags);
+	current->flags &= ~(PF_NO_SETAFFINITY);
+	raw_spin_unlock_irqrestore(&current->pi_lock, flags);
+
 	tlat->count = 0;
 	tlat->tracing_thread = false;
 
@@ -1731,6 +1902,7 @@ static int timerlat_main(void *data)
 	osn_var->sampling = 1;
 
 	while (!kthread_should_stop()) {
+
 		now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer));
 		diff = now - tlat->abs_period;
 
@@ -1749,10 +1921,14 @@ static int timerlat_main(void *data)
 			if (time_to_us(diff) >= osnoise_data.stop_tracing_total)
 				osnoise_stop_tracing();
 
+		if (osnoise_migration_pending())
+			break;
+
 		wait_next_period(tlat);
 	}
 
 	hrtimer_cancel(&tlat->timer);
+	migrate_enable();
 	return 0;
 }
 #else /* CONFIG_TIMERLAT_TRACER */
@@ -1771,10 +1947,24 @@ static void stop_kthread(unsigned int cpu)
 
 	kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;
 	if (kthread) {
-		kthread_stop(kthread);
+		if (test_bit(OSN_WORKLOAD, &osnoise_options)) {
+			kthread_stop(kthread);
+		} else {
+			/*
+			 * This is a user thread waiting on the timerlat_fd. We need
+			 * to close all users, and the best way to guarantee this is
+			 * by killing the thread. NOTE: this is a purpose specific file.
+			 */
+			kill_pid(kthread->thread_pid, SIGKILL, 1);
+			put_task_struct(kthread);
+		}
 		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
 	} else {
+		/* if no workload, just return */
 		if (!test_bit(OSN_WORKLOAD, &osnoise_options)) {
+			/*
+			 * This is set in the osnoise tracer case.
+			 */
 			per_cpu(per_cpu_osnoise_var, cpu).sampling = false;
 			barrier();
 			return;
@@ -1819,7 +2009,6 @@ static int start_kthread(unsigned int cpu)
 			barrier();
 			return 0;
 		}
-
 		snprintf(comm, 24, "osnoise/%d", cpu);
 	}
 
@@ -1848,6 +2037,11 @@ static int start_per_cpu_kthreads(void)
 	int retval = 0;
 	int cpu;
 
+	if (!test_bit(OSN_WORKLOAD, &osnoise_options)) {
+		if (timerlat_enabled())
+			return 0;
+	}
+
 	cpus_read_lock();
 	/*
 	 * Run only on online CPUs in which osnoise is allowed to run.
@@ -2188,6 +2382,223 @@ err_free:
 	return err;
 }
 
+#ifdef CONFIG_TIMERLAT_TRACER
+static int timerlat_fd_open(struct inode *inode, struct file *file)
+{
+	struct osnoise_variables *osn_var;
+	struct timerlat_variables *tlat;
+	long cpu = (long) inode->i_cdev;
+
+	mutex_lock(&interface_lock);
+
+	/*
+	 * This file is accessible only if timerlat is enabled, and
+	 * NO_OSNOISE_WORKLOAD is set.
+	 */
+	if (!timerlat_enabled() || test_bit(OSN_WORKLOAD, &osnoise_options)) {
+		mutex_unlock(&interface_lock);
+		return -EINVAL;
+	}
+
+	migrate_disable();
+
+	osn_var = this_cpu_osn_var();
+
+	/*
+	 * The osn_var->pid holds the single access to this file.
+	 */
+	if (osn_var->pid) {
+		mutex_unlock(&interface_lock);
+		migrate_enable();
+		return -EBUSY;
+	}
+
+	/*
+	 * timerlat tracer is a per-cpu tracer. Check if the user-space too
+	 * is pinned to a single CPU. The tracer laters monitor if the task
+	 * migrates and then disables tracer if it does. However, it is
+	 * worth doing this basic acceptance test to avoid obviusly wrong
+	 * setup.
+	 */
+	if (current->nr_cpus_allowed > 1 ||  cpu != smp_processor_id()) {
+		mutex_unlock(&interface_lock);
+		migrate_enable();
+		return -EPERM;
+	}
+
+	/*
+	 * From now on, it is good to go.
+	 */
+	file->private_data = inode->i_cdev;
+
+	get_task_struct(current);
+
+	osn_var->kthread = current;
+	osn_var->pid = current->pid;
+
+	/*
+	 * Setup is done.
+	 */
+	mutex_unlock(&interface_lock);
+
+	tlat = this_cpu_tmr_var();
+	tlat->count = 0;
+
+	migrate_enable();
+	return 0;
+};
+
+/*
+ * timerlat_fd_read - Read function for "timerlat_fd" file
+ * @file: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * Prints 1 on timerlat, the number of interferences on osnoise, -1 on error.
+ */
+static ssize_t
+timerlat_fd_read(struct file *file, char __user *ubuf, size_t count,
+		  loff_t *ppos)
+{
+	long cpu = (long) file->private_data;
+	struct osnoise_variables *osn_var;
+	struct timerlat_variables *tlat;
+	struct timerlat_sample s;
+	s64 diff;
+	u64 now;
+
+	migrate_disable();
+
+	tlat = this_cpu_tmr_var();
+
+	/*
+	 * While in user-space, the thread is migratable. There is nothing
+	 * we can do about it.
+	 * So, if the thread is running on another CPU, stop the machinery.
+	 */
+	if (cpu == smp_processor_id()) {
+		if (tlat->uthread_migrate) {
+			migrate_enable();
+			return -EINVAL;
+		}
+	} else {
+		per_cpu_ptr(&per_cpu_timerlat_var, cpu)->uthread_migrate = 1;
+		osnoise_taint("timerlat user thread migrate\n");
+		osnoise_stop_tracing();
+		migrate_enable();
+		return -EINVAL;
+	}
+
+	osn_var = this_cpu_osn_var();
+
+	/*
+	 * The timerlat in user-space runs in a different order:
+	 * the read() starts from the execution of the previous occurrence,
+	 * sleeping for the next occurrence.
+	 *
+	 * So, skip if we are entering on read() before the first wakeup
+	 * from timerlat IRQ:
+	 */
+	if (likely(osn_var->sampling)) {
+		now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer));
+		diff = now - tlat->abs_period;
+
+		/*
+		 * it was not a timer firing, but some other signal?
+		 */
+		if (diff < 0)
+			goto out;
+
+		s.seqnum = tlat->count;
+		s.timer_latency = diff;
+		s.context = THREAD_URET;
+
+		trace_timerlat_sample(&s);
+
+		notify_new_max_latency(diff);
+
+		tlat->tracing_thread = false;
+		if (osnoise_data.stop_tracing_total)
+			if (time_to_us(diff) >= osnoise_data.stop_tracing_total)
+				osnoise_stop_tracing();
+	} else {
+		tlat->tracing_thread = false;
+		tlat->kthread = current;
+
+		hrtimer_init(&tlat->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
+		tlat->timer.function = timerlat_irq;
+
+		/* Annotate now to drift new period */
+		tlat->abs_period = hrtimer_cb_get_time(&tlat->timer);
+
+		osn_var->sampling = 1;
+	}
+
+	/* wait for the next period */
+	wait_next_period(tlat);
+
+	/* This is the wakeup from this cycle */
+	now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer));
+	diff = now - tlat->abs_period;
+
+	/*
+	 * it was not a timer firing, but some other signal?
+	 */
+	if (diff < 0)
+		goto out;
+
+	s.seqnum = tlat->count;
+	s.timer_latency = diff;
+	s.context = THREAD_CONTEXT;
+
+	trace_timerlat_sample(&s);
+
+	if (osnoise_data.stop_tracing_total) {
+		if (time_to_us(diff) >= osnoise_data.stop_tracing_total) {
+			timerlat_dump_stack(time_to_us(diff));
+			notify_new_max_latency(diff);
+			osnoise_stop_tracing();
+		}
+	}
+
+out:
+	migrate_enable();
+	return 0;
+}
+
+static int timerlat_fd_release(struct inode *inode, struct file *file)
+{
+	struct osnoise_variables *osn_var;
+	struct timerlat_variables *tlat_var;
+	long cpu = (long) file->private_data;
+
+	migrate_disable();
+	mutex_lock(&interface_lock);
+
+	osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu);
+	tlat_var = per_cpu_ptr(&per_cpu_timerlat_var, cpu);
+
+	hrtimer_cancel(&tlat_var->timer);
+	memset(tlat_var, 0, sizeof(*tlat_var));
+
+	osn_var->sampling = 0;
+	osn_var->pid = 0;
+
+	/*
+	 * We are leaving, not being stopped... see stop_kthread();
+	 */
+	if (osn_var->kthread) {
+		put_task_struct(osn_var->kthread);
+		osn_var->kthread = NULL;
+	}
+
+	mutex_unlock(&interface_lock);
+	migrate_enable();
+	return 0;
+}
+#endif
+
 /*
  * osnoise/runtime_us: cannot be greater than the period.
  */
@@ -2251,6 +2662,13 @@ static struct trace_min_max_param timerlat_period = {
 	.max	= &timerlat_max_period,
 	.min	= &timerlat_min_period,
 };
+
+static const struct file_operations timerlat_fd_fops = {
+	.open		= timerlat_fd_open,
+	.read		= timerlat_fd_read,
+	.release	= timerlat_fd_release,
+	.llseek		= generic_file_llseek,
+};
 #endif
 
 static const struct file_operations cpus_fops = {
@@ -2288,18 +2706,63 @@ static int init_timerlat_stack_tracefs(struct dentry *top_dir)
 }
 #endif /* CONFIG_STACKTRACE */
 
+static int osnoise_create_cpu_timerlat_fd(struct dentry *top_dir)
+{
+	struct dentry *timerlat_fd;
+	struct dentry *per_cpu;
+	struct dentry *cpu_dir;
+	char cpu_str[30]; /* see trace.c: tracing_init_tracefs_percpu() */
+	long cpu;
+
+	/*
+	 * Why not using tracing instance per_cpu/ dir?
+	 *
+	 * Because osnoise/timerlat have a single workload, having
+	 * multiple files like these are wast of memory.
+	 */
+	per_cpu = tracefs_create_dir("per_cpu", top_dir);
+	if (!per_cpu)
+		return -ENOMEM;
+
+	for_each_possible_cpu(cpu) {
+		snprintf(cpu_str, 30, "cpu%ld", cpu);
+		cpu_dir = tracefs_create_dir(cpu_str, per_cpu);
+		if (!cpu_dir)
+			goto out_clean;
+
+		timerlat_fd = trace_create_file("timerlat_fd", TRACE_MODE_READ,
+						cpu_dir, NULL, &timerlat_fd_fops);
+		if (!timerlat_fd)
+			goto out_clean;
+
+		/* Record the CPU */
+		d_inode(timerlat_fd)->i_cdev = (void *)(cpu);
+	}
+
+	return 0;
+
+out_clean:
+	tracefs_remove(per_cpu);
+	return -ENOMEM;
+}
+
 /*
  * init_timerlat_tracefs - A function to initialize the timerlat interface files
  */
 static int init_timerlat_tracefs(struct dentry *top_dir)
 {
 	struct dentry *tmp;
+	int retval;
 
 	tmp = tracefs_create_file("timerlat_period_us", TRACE_MODE_WRITE, top_dir,
 				  &timerlat_period, &trace_min_max_fops);
 	if (!tmp)
 		return -ENOMEM;
 
+	retval = osnoise_create_cpu_timerlat_fd(top_dir);
+	if (retval)
+		return retval;
+
 	return init_timerlat_stack_tracefs(top_dir);
 }
 #else /* CONFIG_TIMERLAT_TRACER */
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 1e33f367783e..db575094c498 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1446,6 +1446,8 @@ static struct trace_event trace_osnoise_event = {
 };
 
 /* TRACE_TIMERLAT */
+
+static char *timerlat_lat_context[] = {"irq", "thread", "user-ret"};
 static enum print_line_t
 trace_timerlat_print(struct trace_iterator *iter, int flags,
 		     struct trace_event *event)
@@ -1458,7 +1460,7 @@ trace_timerlat_print(struct trace_iterator *iter, int flags,
 
 	trace_seq_printf(s, "#%-5u context %6s timer_latency %9llu ns\n",
 			 field->seqnum,
-			 field->context ? "thread" : "irq",
+			 timerlat_lat_context[field->context],
 			 field->timer_latency);
 
 	return trace_handle_return(s);