tracing: Allow stacktraces to be saved as histogram variables

Allow to save stacktraces into a histogram variable. This will be used by
synthetic events to allow a stacktrace from one event to be passed and
displayed by another event.

The special keyword "stacktrace" is to be used to trigger a stack
trace for the event that the histogram trigger is attached to.

  echo 'hist:keys=pid:st=stacktrace" > events/sched/sched_waking/trigger

Currently nothing can get access to the "$st" variable above that contains
the stack trace, but that will soon change.

Link: https://lkml.kernel.org/r/20230117152235.856323729@goodmis.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Ching-lin Yu <chinglinyu@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 5edbf6b1da3f311805218c252dd4559d249585e0..f8f67e17898ae85c2e878d9ff1c675ae25592cb8 100644 (file)
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1360,6 +1360,8 @@ static const char *hist_field_name(struct hist_field *field,
                        field_name = field->name;
        } else if (field->flags & HIST_FIELD_FL_TIMESTAMP)
                field_name = "common_timestamp";
+       else if (field->flags & HIST_FIELD_FL_STACKTRACE)
+               field_name = "stacktrace";
        else if (field->flags & HIST_FIELD_FL_HITCOUNT)
                field_name = "hitcount";
 
@@ -1980,6 +1982,10 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 
        if (flags & HIST_FIELD_FL_STACKTRACE) {
                hist_field->fn_num = HIST_FIELD_FN_NOP;
+               hist_field->size = HIST_STACKTRACE_SIZE;
+               hist_field->type = kstrdup_const("unsigned long[]", GFP_KERNEL);
+               if (!hist_field->type)
+                       goto free;
                goto out;
        }
 
@@ -2351,6 +2357,8 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
                hist_data->enable_timestamps = true;
                if (*flags & HIST_FIELD_FL_TIMESTAMP_USECS)
                        hist_data->attrs->ts_in_usecs = true;
+       } else if (strcmp(field_name, "stacktrace") == 0) {
+               *flags |= HIST_FIELD_FL_STACKTRACE;
        } else if (strcmp(field_name, "common_cpu") == 0)
                *flags |= HIST_FIELD_FL_CPU;
        else if (strcmp(field_name, "hitcount") == 0)
@@ -3119,13 +3127,24 @@ static inline void __update_field_vars(struct tracing_map_elt *elt,
                var_val = hist_fn_call(val, elt, buffer, rbe, rec);
                var_idx = var->var.idx;
 
-               if (val->flags & HIST_FIELD_FL_STRING) {
+               if (val->flags & (HIST_FIELD_FL_STRING |
+                                 HIST_FIELD_FL_STACKTRACE)) {
                        char *str = elt_data->field_var_str[j++];
                        char *val_str = (char *)(uintptr_t)var_val;
                        unsigned int size;
 
-                       size = min(val->size, STR_VAR_LEN_MAX);
-                       strscpy(str, val_str, size);
+                       if (val->flags & HIST_FIELD_FL_STRING) {
+                               size = min(val->size, STR_VAR_LEN_MAX);
+                               strscpy(str, val_str, size);
+                       } else {
+                               int e;
+
+                               e = stack_trace_save((void *)str,
+                                                    HIST_STACKTRACE_DEPTH,
+                                                    HIST_STACKTRACE_SKIP);
+                               if (e < HIST_STACKTRACE_DEPTH - 1)
+                                       ((unsigned long *)str)[e] = 0;
+                       }
                        var_val = (u64)(uintptr_t)str;
                }
                tracing_map_set_var(elt, var_idx, var_val);
@@ -3824,7 +3843,8 @@ static void save_field_var(struct hist_trigger_data *hist_data,
 {
        hist_data->field_vars[hist_data->n_field_vars++] = field_var;
 
-       if (field_var->val->flags & HIST_FIELD_FL_STRING)
+       /* Stack traces are saved in the string storage too */
+       if (field_var->val->flags & (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE))
                hist_data->n_field_var_str++;
 }
 
@@ -4103,7 +4123,8 @@ static int action_create(struct hist_trigger_data *hist_data,
                        }
 
                        hist_data->save_vars[hist_data->n_save_vars++] = field_var;
-                       if (field_var->val->flags & HIST_FIELD_FL_STRING)
+                       if (field_var->val->flags &
+                           (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE))
                                hist_data->n_save_var_str++;
                        kfree(param);
                }
@@ -4351,7 +4372,8 @@ static int create_var_field(struct hist_trigger_data *hist_data,
        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)
+       if (!ret && hist_data->fields[val_idx]->flags &
+           (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE))
                hist_data->fields[val_idx]->var_str_idx = hist_data->n_var_str++;
 
        return ret;
@@ -5092,7 +5114,8 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
                if (hist_field->flags & HIST_FIELD_FL_VAR) {
                        var_idx = hist_field->var.idx;
 
-                       if (hist_field->flags & HIST_FIELD_FL_STRING) {
+                       if (hist_field->flags &
+                           (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE)) {
                                unsigned int str_start, var_str_idx, idx;
                                char *str, *val_str;
                                unsigned int size;
@@ -5105,9 +5128,18 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
                                str = elt_data->field_var_str[idx];
                                val_str = (char *)(uintptr_t)hist_val;
 
-                               size = min(hist_field->size, STR_VAR_LEN_MAX);
-                               strscpy(str, val_str, size);
-
+                               if (hist_field->flags & HIST_FIELD_FL_STRING) {
+                                       size = min(hist_field->size, STR_VAR_LEN_MAX);
+                                       strscpy(str, val_str, size);
+                               } else {
+                                       int e;
+
+                                       e = stack_trace_save((void *)str,
+                                                            HIST_STACKTRACE_DEPTH,
+                                                            HIST_STACKTRACE_SKIP);
+                                       if (e < HIST_STACKTRACE_DEPTH - 1)
+                                               ((unsigned long *)str)[e] = 0;
+                               }
                                hist_val = (u64)(uintptr_t)str;
                        }
                        tracing_map_set_var(elt, var_idx, hist_val);