Re: [RFC][PATCH 3/4] tracing: Add infrastructure to allow set_event_pid to follow children

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On Apr 19, 2016, at 10:34 AM, rostedt rostedt@goodmis.org wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> 
> Add the infrastructure needed to have the PIDs in set_event_pid to
> automatically add PIDs of the children of the tasks that have their PIDs in
> set_event_pid. This will also remove PIDs from set_event_pid when a task
> exits
> 
> This is implemented by adding hooks into the fork and exit tracepoints. On
> fork, the PIDs are added to the list, and on exit, they are removed.
> 
> Add a new option called event_fork that when set, PIDs in set_event_pid will
> automatically get their children PIDs added when they fork, as well as any
> task that exits will have its PID removed from set_event_pid.

Just out of curiosity: how does it deal with multi-process and multi-thread ?
What events are expected in each case ?

Thanks,

Mathieu

> 
> This works for instances as well.
> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> kernel/trace/trace.c        |  3 ++
> kernel/trace/trace.h        |  2 ++
> kernel/trace/trace_events.c | 84 +++++++++++++++++++++++++++++++++++++++------
> 3 files changed, 79 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a2f0b9f33e9b..0d12dbde8399 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3571,6 +3571,9 @@ int set_tracer_flag(struct trace_array *tr, unsigned int
> mask, int enabled)
> 	if (mask == TRACE_ITER_RECORD_CMD)
> 		trace_event_enable_cmd_record(enabled);
> 
> +	if (mask == TRACE_ITER_EVENT_FORK)
> +		trace_event_follow_fork(tr, enabled);
> +
> 	if (mask == TRACE_ITER_OVERWRITE) {
> 		ring_buffer_change_overwrite(tr->trace_buffer.buffer, enabled);
> #ifdef CONFIG_TRACER_MAX_TRACE
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 68cbb8e10aea..2525042760e6 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -655,6 +655,7 @@ static inline void __trace_stack(struct trace_array *tr,
> unsigned long flags,
> extern cycle_t ftrace_now(int cpu);
> 
> extern void trace_find_cmdline(int pid, char comm[]);
> +extern void trace_event_follow_fork(struct trace_array *tr, bool enable);
> 
> #ifdef CONFIG_DYNAMIC_FTRACE
> extern unsigned long ftrace_update_tot_cnt;
> @@ -966,6 +967,7 @@ extern int trace_get_user(struct trace_parser *parser, const
> char __user *ubuf,
> 		C(STOP_ON_FREE,		"disable_on_free"),	\
> 		C(IRQ_INFO,		"irq-info"),		\
> 		C(MARKERS,		"markers"),		\
> +		C(EVENT_FORK,		"event-fork"),		\
> 		FUNCTION_FLAGS					\
> 		FGRAPH_FLAGS					\
> 		STACK_FLAGS					\
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 45f7cc72bf25..add81dff7520 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -474,11 +474,23 @@ static void ftrace_clear_events(struct trace_array *tr)
> /* Shouldn't this be in a header? */
> extern int pid_max;
> 
> +/* Returns true if found in filter */
> static bool
> -ignore_this_task(struct trace_pid_list *filtered_pids, struct task_struct
> *task)
> +find_filtered_pid(struct trace_pid_list *filtered_pids, pid_t search_pid)
> {
> -	pid_t pid;
> +	/*
> +	 * If pid_max changed after filtered_pids was created, we
> +	 * by default ignore all pids greater than the previous pid_max.
> +	 */
> +	if (search_pid >= filtered_pids->pid_max)
> +		return false;
> +
> +	return test_bit(search_pid, filtered_pids->pids);
> +}
> 
> +static bool
> +ignore_this_task(struct trace_pid_list *filtered_pids, struct task_struct
> *task)
> +{
> 	/*
> 	 * Return false, because if filtered_pids does not exist,
> 	 * all pids are good to trace.
> @@ -486,16 +498,68 @@ ignore_this_task(struct trace_pid_list *filtered_pids,
> struct task_struct *task)
> 	if (!filtered_pids)
> 		return false;
> 
> -	pid = task->pid;
> +	return !find_filtered_pid(filtered_pids, task->pid);
> +}
> 
> -	/*
> -	 * If pid_max changed after filtered_pids was created, we
> -	 * by default ignore all pids greater than the previous pid_max.
> -	 */
> -	if (task->pid >= filtered_pids->pid_max)
> -		return true;
> +static void filter_add_remove_task(struct trace_pid_list *pid_list,
> +				   struct task_struct *self,
> +				   struct task_struct *task)
> +{
> +	if (!pid_list)
> +		return;
> +
> +	/* For forks, we only add if the forking task is listed */
> +	if (self) {
> +		if (!find_filtered_pid(pid_list, self->pid))
> +			return;
> +	}
> +
> +	/* Sorry, but we don't support pid_max changing after setting */
> +	if (task->pid >= pid_list->pid_max)
> +		return;
> +
> +	/* "self" is set for forks, and NULL for exits */
> +	if (self)
> +		set_bit(task->pid, pid_list->pids);
> +	else
> +		clear_bit(task->pid, pid_list->pids);
> +}
> +
> +static void
> +event_filter_pid_sched_process_exit(void *data, struct task_struct *task)
> +{
> +	struct trace_pid_list *pid_list;
> +	struct trace_array *tr = data;
> +
> +	pid_list = rcu_dereference_sched(tr->filtered_pids);
> +	filter_add_remove_task(pid_list, NULL, task);
> +}
> 
> -	return !test_bit(task->pid, filtered_pids->pids);
> +static void
> +event_filter_pid_sched_process_fork(void *data,
> +				    struct task_struct *self,
> +				    struct task_struct *task)
> +{
> +	struct trace_pid_list *pid_list;
> +	struct trace_array *tr = data;
> +
> +	pid_list = rcu_dereference_sched(tr->filtered_pids);
> +	filter_add_remove_task(pid_list, self, task);
> +}
> +
> +void trace_event_follow_fork(struct trace_array *tr, bool enable)
> +{
> +	if (enable) {
> +		register_trace_prio_sched_process_fork(event_filter_pid_sched_process_fork,
> +						       tr, INT_MIN);
> +		register_trace_prio_sched_process_exit(event_filter_pid_sched_process_exit,
> +						       tr, INT_MAX);
> +	} else {
> +		unregister_trace_sched_process_fork(event_filter_pid_sched_process_fork,
> +						    tr);
> +		unregister_trace_sched_process_exit(event_filter_pid_sched_process_exit,
> +						    tr);
> +	}
> }
> 
> static void
> --
> 2.8.0.rc3
> 
> 
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-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com