[for-linus][PATCH 04/15] tracing: Save normal string variables

Steven Rostedt
2020-10-06T14:35:34Z

From: Tom Zanussi <zanussi@kernel.org>

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>
---
kernel/trace/trace_events_hist.c | 34 ++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 3b22e2122d1a..812bc5f94b5c 100644
--- 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;
}
--
2.28.0