Patch "tracing: Save normal string variables" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tracing: Save normal string variables

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tracing-save-normal-string-variables.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1d4e27b43b5af59861031546b26b087d8aec68e3
Author: Tom Zanussi <zanussi@xxxxxxxxxx>
Date:   Sun Oct 4 17:14:05 2020 -0500

    tracing: Save normal string variables
    
    [ Upstream commit 63a1e5de3006f4ad713e4d72bcb404d0301e853d ]
    
    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@xxxxxxxxxx
    
    Fixes: 02205a6752f2 (tracing: Add support for 'field variables')
    Signed-off-by: Tom Zanussi <zanussi@xxxxxxxxxx>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f63766366e238..9a73c187d241e 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -149,6 +149,8 @@ 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,
@@ -351,6 +353,7 @@ 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;
@@ -2305,7 +2308,12 @@ 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;
+	}
 
 	size = STR_VAR_LEN_MAX;
 
@@ -4599,6 +4607,7 @@ 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;
@@ -4613,7 +4622,12 @@ 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,
@@ -5333,6 +5347,22 @@ 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;
 		}