From: Tom Zanussi <zanussi@kernel.org>
Date: Sun, 4 Oct 2020 17:14:05 -0500
Subject: tracing: Save normal string variables
Git-commit: 63a1e5de3006f4ad713e4d72bcb404d0301e853d
Patch-mainline: v5.10-rc1
References: git-fixes

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>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 kernel/trace/trace_events_hist.c |   34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -148,6 +148,8 @@ 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,
@@ -350,6 +352,7 @@ 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;
@@ -2257,7 +2260,12 @@ static int hist_trigger_elt_data_alloc(s
 		}
 	}
 
-	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));
 
@@ -4500,6 +4508,7 @@ static int create_var_field(struct hist_
 {
 	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;
@@ -4514,7 +4523,12 @@ static int create_var_field(struct hist_
 	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,
@@ -5241,6 +5255,22 @@ static void hist_trigger_elt_update(stru
 		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;
 		}