[PATCH V4 04/19] trace/osnoise: Support a list of trace_array *tr

Daniel Bristot de Oliveira
2021-10-21T12:58:54Z

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.

Cc: Steven Rostedt <rostedt@goodmis.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>
---
kernel/trace/trace_osnoise.c | 253 +++++++++++++++++++++++++----------
1 file changed, 184 insertions(+), 69 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 9b9e6bc889e9..a6d8f514bd7c 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/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 +48,73 @@ 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;
+
+ 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;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+ if (inst->tr == tr) {
+ list_del_rcu(&inst->list);
+ found = 1;
+ break;
+ }
+ }
+ rcu_read_unlock();
+
+ if (!found) {
+ WARN("osnoise unregister did not find tr %s\n", tr->name);
+ return;
+ }
+
+ synchronize_rcu();
+ kfree(inst);
+}
+
/*
* NMI runtime info.
*/
@@ -248,11 +313,6 @@ 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 +375,24 @@ 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 +415,22 @@ 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.
@@ -387,14 +468,10 @@ 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;

@@ -411,6 +488,22 @@ 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
@@ -450,29 +543,18 @@ 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);

@@ -481,8 +563,29 @@ 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
@@ -1077,12 +1180,37 @@ 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();
+}

- trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_,
- "stop tracing hit on cpu %d\n", smp_processor_id());
+/*
+ * notify_new_max_latency - Notify a new max latency via fsnotify interface.
+ */
+void notify_new_max_latency(u64 latency)
+{
+ struct osnoise_instance *inst;
+ struct trace_array *tr;

- tracer_tracing_off(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();
}

/*
@@ -1096,7 +1224,6 @@ 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;
@@ -1231,11 +1358,7 @@ 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)
@@ -1293,7 +1416,6 @@ 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;
@@ -1364,11 +1486,7 @@ 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 +1699,7 @@ 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 +1834,10 @@ 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();

@@ -1941,8 +2058,6 @@ static int osnoise_workload_start(void)
return retval;
}

- osnoise_busy = true;
-
return 0;
}

@@ -1951,7 +2066,7 @@ 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;
@@ -1962,28 +2077,28 @@ 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();
}

@@ -1991,14 +2106,12 @@ 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;
}

@@ -2022,7 +2135,7 @@ 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;
@@ -2031,6 +2144,8 @@ 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");
@@ -2040,7 +2155,7 @@ 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)
@@ -2054,11 +2169,9 @@ 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);
@@ -2105,6 +2218,8 @@ __init static int init_osnoise_tracer(void)
#endif
osnoise_init_hotplug_support();

+ INIT_LIST_HEAD_RCU(&osnoise_instances);
+
init_tracefs();

return 0;
--
2.31.1