Re: [PATCH] tracing/user_events: Optimize safe list traversals

[Beau Belgrave]

On Thu, Aug 10, 2023 at 12:43:37PM -0700, Eric Vaughn wrote:
> Several of the list traversals in the user_events facility use safe list
> traversals where they could be using the unsafe versions instead.
> 
> Replace these safe traversals with their unsafe counterparts in the
> interest of optimization.
> 
> Suggested-by: Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Eric Vaughn <ervaughn@xxxxxxxxxxxxxxxxxxx>
> ---

Thanks for doing this, it looks good to me.

Acked-by: Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx>

Thanks,
-Beau

>  kernel/trace/trace_events_user.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index 33cb6af31f39..6f046650e527 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -1328,14 +1328,14 @@ static int user_field_set_string(struct ftrace_event_field *field,
>  
>  static int user_event_set_print_fmt(struct user_event *user, char *buf, int len)
>  {
> -	struct ftrace_event_field *field, *next;
> +	struct ftrace_event_field *field;
>  	struct list_head *head = &user->fields;
>  	int pos = 0, depth = 0;
>  	const char *str_func;
>  
>  	pos += snprintf(buf + pos, LEN_OR_ZERO, "\"");
>  
> -	list_for_each_entry_safe_reverse(field, next, head, link) {
> +	list_for_each_entry_reverse(field, head, link) {
>  		if (depth != 0)
>  			pos += snprintf(buf + pos, LEN_OR_ZERO, " ");
>  
> @@ -1347,7 +1347,7 @@ static int user_event_set_print_fmt(struct user_event *user, char *buf, int len)
>  
>  	pos += snprintf(buf + pos, LEN_OR_ZERO, "\"");
>  
> -	list_for_each_entry_safe_reverse(field, next, head, link) {
> +	list_for_each_entry_reverse(field, head, link) {
>  		if (user_field_is_dyn_string(field->type, &str_func))
>  			pos += snprintf(buf + pos, LEN_OR_ZERO,
>  					", %s(%s)", str_func, field->name);
> @@ -1732,7 +1732,7 @@ static int user_event_create(const char *raw_command)
>  static int user_event_show(struct seq_file *m, struct dyn_event *ev)
>  {
>  	struct user_event *user = container_of(ev, struct user_event, devent);
> -	struct ftrace_event_field *field, *next;
> +	struct ftrace_event_field *field;
>  	struct list_head *head;
>  	int depth = 0;
>  
> @@ -1740,7 +1740,7 @@ static int user_event_show(struct seq_file *m, struct dyn_event *ev)
>  
>  	head = trace_get_fields(&user->call);
>  
> -	list_for_each_entry_safe_reverse(field, next, head, link) {
> +	list_for_each_entry_reverse(field, head, link) {
>  		if (depth == 0)
>  			seq_puts(m, " ");
>  		else
> @@ -1816,13 +1816,14 @@ static bool user_field_match(struct ftrace_event_field *field, int argc,
>  static bool user_fields_match(struct user_event *user, int argc,
>  			      const char **argv)
>  {
> -	struct ftrace_event_field *field, *next;
> +	struct ftrace_event_field *field;
>  	struct list_head *head = &user->fields;
>  	int i = 0;
>  
> -	list_for_each_entry_safe_reverse(field, next, head, link)
> +	list_for_each_entry_reverse(field, head, link) {
>  		if (!user_field_match(field, argc, argv, &i))
>  			return false;
> +	}
>  
>  	if (i != argc)
>  		return false;
> -- 
> 2.34.1