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

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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