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

Steven Rostedt
2021-10-23T02:38:45Z

On Thu, 21 Oct 2021 14:56:42 +0200
Daniel Bristot de Oliveira <bristot@kernel.org> wrote:

> 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);

Adding to the list requires more than RCU protection, and if this has
that protection there's no reason for using rcu to protect here.

[ Added Paul to comment about this too ]

-- Steve

> + 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;