tracing: Allow execnames to be passed as args for synthetic events

Allow common_pid.execname to be saved in a variable in one histogram to be
passed to another histogram that can pass it as a parameter to a synthetic
event.

 ># echo 'hist:keys=pid:__arg__1=common_timestamp.usecs:arg2=common_pid.execname' \
       > events/sched/sched_waking/trigger
 ># echo 'wakeup_lat s32 pid; u64 delta; char wake_comm[]' > synthetic_events
 ># echo 'hist:keys=next_pid:pid=next_pid,delta=common_timestamp.usecs-$__arg__1,exec=$arg2'\
':onmatch(sched.sched_waking).trace(wakeup_lat,$pid,$delta,$exec)' \
 > events/sched/sched_switch/trigger

The above is a wake up latency synthetic event setup that passes the execname
of the common_pid that woke the task to the scheduling of that task, which
triggers a synthetic event that passes the original execname as a
parameter to display it.

 ># echo 1 > events/synthetic/enable
 ># cat trace
    <idle>-0       [006] d..4   186.863801: wakeup_lat: pid=1306 delta=65 wake_comm=kworker/u16:3
    <idle>-0       [000] d..4   186.863858: wakeup_lat: pid=163 delta=27 wake_comm=<idle>
    <idle>-0       [001] d..4   186.863903: wakeup_lat: pid=1307 delta=36 wake_comm=kworker/u16:4
    <idle>-0       [000] d..4   186.863927: wakeup_lat: pid=163 delta=5 wake_comm=<idle>
    <idle>-0       [006] d..4   186.863957: wakeup_lat: pid=1306 delta=24 wake_comm=kworker/u16:3
      sshd-1306    [006] d..4   186.864051: wakeup_lat: pid=61 delta=62 wake_comm=<idle>
    <idle>-0       [000] d..4   186.965030: wakeup_lat: pid=609 delta=18 wake_comm=<idle>
    <idle>-0       [006] d..4   186.987582: wakeup_lat: pid=1306 delta=65 wake_comm=kworker/u16:3
    <idle>-0       [000] d..4   186.987639: wakeup_lat: pid=163 delta=27 wake_comm=<idle>

Link: https://lkml.kernel.org/r/20210722142837.458596338@goodmis.org
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index bb466a82b938e0b16c22ff30b8df1d500868c80f..9d91b1c06957b7d5e5f572e49c22e0869762dbe1 100644 (file)
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1420,17 +1420,17 @@ static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
        struct hist_trigger_data *hist_data = elt->map->private_data;
        unsigned int size = TASK_COMM_LEN;
        struct hist_elt_data *elt_data;
-       struct hist_field *key_field;
+       struct hist_field *hist_field;
        unsigned int i, n_str;
 
        elt_data = kzalloc(sizeof(*elt_data), GFP_KERNEL);
        if (!elt_data)
                return -ENOMEM;
 
-       for_each_hist_key_field(i, hist_data) {
-               key_field = hist_data->fields[i];
+       for_each_hist_field(i, hist_data) {
+               hist_field = hist_data->fields[i];
 
-               if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
+               if (hist_field->flags & HIST_FIELD_FL_EXECNAME) {
                        elt_data->comm = kzalloc(size, GFP_KERNEL);
                        if (!elt_data->comm) {
                                kfree(elt_data);
@@ -3771,6 +3771,41 @@ static int create_val_field(struct hist_trigger_data *hist_data,
        return __create_val_field(hist_data, val_idx, file, NULL, field_str, 0);
 }
 
+static const char *no_comm = "(no comm)";
+
+static u64 hist_field_execname(struct hist_field *hist_field,
+                              struct tracing_map_elt *elt,
+                              struct trace_buffer *buffer,
+                              struct ring_buffer_event *rbe,
+                              void *event)
+{
+       struct hist_elt_data *elt_data;
+
+       if (WARN_ON_ONCE(!elt))
+               return (u64)(unsigned long)no_comm;
+
+       elt_data = elt->private_data;
+
+       if (WARN_ON_ONCE(!elt_data->comm))
+               return (u64)(unsigned long)no_comm;
+
+       return (u64)(unsigned long)(elt_data->comm);
+}
+
+/* Convert a var that points to common_pid.execname to a string */
+static void update_var_execname(struct hist_field *hist_field)
+{
+       hist_field->flags = HIST_FIELD_FL_STRING | HIST_FIELD_FL_VAR |
+               HIST_FIELD_FL_EXECNAME;
+       hist_field->size = MAX_FILTER_STR_VAL;
+       hist_field->is_signed = 0;
+
+       kfree_const(hist_field->type);
+       hist_field->type = "char[]";
+
+       hist_field->fn = hist_field_execname;
+}
+
 static int create_var_field(struct hist_trigger_data *hist_data,
                            unsigned int val_idx,
                            struct trace_event_file *file,
@@ -3795,6 +3830,9 @@ static int create_var_field(struct hist_trigger_data *hist_data,
 
        ret = __create_val_field(hist_data, val_idx, file, var_name, expr_str, flags);
 
+       if (!ret && hist_data->fields[val_idx]->flags & HIST_FIELD_FL_EXECNAME)
+               update_var_execname(hist_data->fields[val_idx]);
+
        if (!ret && hist_data->fields[val_idx]->flags & HIST_FIELD_FL_STRING)
                hist_data->fields[val_idx]->var_str_idx = hist_data->n_var_str++;