tracing: Save normal string variables

String variables created as field variables and save variables are
already handled properly by having their values copied when set.  The
same isn't done for normal variables, but needs to be - simply saving
a pointer to a string contained in an old event isn't sufficient,
since that event's data may quickly become overwritten and therefore a
string pointer to it could yield garbage.

This change uses the same mechanism as field variables and simply
appends the new strings to the existing per-element field_var_str[]
array allocated for that purpose.

Link: https://lkml.kernel.org/r/1c1a03798b02e67307412a0c719d1bfb69b13007.1601848695.git.zanussi@kernel.org
Fixes: 02205a6752f2 (tracing: Add support for 'field variables')
Signed-off-by: Tom Zanussi <zanussi@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 3b22e2122d1a0a764584dd54ca9fde15f0cdb3c6..812bc5f94b5c3009f51eecba8c2e434f646ce5a7 100644 (file)
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -147,6 +147,8 @@ struct hist_field {
         */
        unsigned int                    var_ref_idx;
        bool                            read_once;
+
+       unsigned int                    var_str_idx;
 };
 
 static u64 hist_field_none(struct hist_field *field,
@@ -349,6 +351,7 @@ struct hist_trigger_data {
        unsigned int                    n_keys;
        unsigned int                    n_fields;
        unsigned int                    n_vars;
+       unsigned int                    n_var_str;
        unsigned int                    key_size;
        struct tracing_map_sort_key     sort_keys[TRACING_MAP_SORT_KEYS_MAX];
        unsigned int                    n_sort_keys;
@@ -1396,7 +1399,12 @@ static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
                }
        }
 
-       n_str = hist_data->n_field_var_str + hist_data->n_save_var_str;
+       n_str = hist_data->n_field_var_str + hist_data->n_save_var_str +
+               hist_data->n_var_str;
+       if (n_str > SYNTH_FIELDS_MAX) {
+               hist_elt_data_free(elt_data);
+               return -EINVAL;
+       }
 
        BUILD_BUG_ON(STR_VAR_LEN_MAX & (sizeof(u64) - 1));
 
@@ -3653,6 +3661,7 @@ static int create_var_field(struct hist_trigger_data *hist_data,
 {
        struct trace_array *tr = hist_data->event_file->tr;
        unsigned long flags = 0;
+       int ret;
 
        if (WARN_ON(val_idx >= TRACING_MAP_VALS_MAX + TRACING_MAP_VARS_MAX))
                return -EINVAL;
@@ -3667,7 +3676,12 @@ static int create_var_field(struct hist_trigger_data *hist_data,
        if (WARN_ON(hist_data->n_vars > TRACING_MAP_VARS_MAX))
                return -EINVAL;
 
-       return __create_val_field(hist_data, val_idx, file, var_name, expr_str, flags);
+       ret = __create_val_field(hist_data, val_idx, file, var_name, expr_str, flags);
+
+       if (hist_data->fields[val_idx]->flags & HIST_FIELD_FL_STRING)
+               hist_data->fields[val_idx]->var_str_idx = hist_data->n_var_str++;
+
+       return ret;
 }
 
 static int create_val_fields(struct hist_trigger_data *hist_data,
@@ -4394,6 +4408,22 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
                hist_val = hist_field->fn(hist_field, elt, rbe, rec);
                if (hist_field->flags & HIST_FIELD_FL_VAR) {
                        var_idx = hist_field->var.idx;
+
+                       if (hist_field->flags & HIST_FIELD_FL_STRING) {
+                               unsigned int str_start, var_str_idx, idx;
+                               char *str, *val_str;
+
+                               str_start = hist_data->n_field_var_str +
+                                       hist_data->n_save_var_str;
+                               var_str_idx = hist_field->var_str_idx;
+                               idx = str_start + var_str_idx;
+
+                               str = elt_data->field_var_str[idx];
+                               val_str = (char *)(uintptr_t)hist_val;
+                               strscpy(str, val_str, STR_VAR_LEN_MAX);
+
+                               hist_val = (u64)(uintptr_t)str;
+                       }
                        tracing_map_set_var(elt, var_idx, hist_val);
                        continue;
                }