Re: [RFC PATCH v2 3/3] tracing: Freeable reserved ring buffer

Steven Rostedt
2025-02-11T00:13:48Z

On Tue, 11 Feb 2025 00:44:17 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> @@ -9857,8 +9861,10 @@ static int __remove_instance(struct trace_array *tr)
> int i;
>
> /* Reference counter for a newly created trace array = 1. */
> - if (tr->ref > 1 || (tr->current_trace && tr->trace_ref))
> + if (tr->ref > 1 || (tr->current_trace && tr->trace_ref)) {
> + pr_info("Instance is busy: ref %d trace_ref %d\n", tr->ref, tr->trace_ref);

I don't think we need the print. The function will error with -EBUSY
letting the user know that it is busy. This is a very common error, where I
found that I had a program that didn't completely die, and still had a file
descriptor open on an instance, and when I go to remove it, I get:

# cd /sys/kernel/tracing/
# mkdir instances/foo
# bash 5< instances/foo/events/enable
# rmdir instances/foo
rmdir: failed to remove 'instances/foo': Device or resource busy
# exit
# rmdir instances/foo
#

If you only have it for debugging that is fine, but we should remove it
before we accept it.

-- Steve

> return -EBUSY;
> + }
>
> list_del(&tr->list);
>
> @@ -9881,6 +9887,11 @@ static int __remove_instance(struct trace_array *tr)
> free_trace_buffers(tr);
> clear_tracing_err_log(tr);
>
> + if (tr->range_name) {
> + reserved_mem_release_by_name(tr->range_name);
> + kfree(tr->range_name);
> + }
> +
> for (i = 0; i < tr->nr_topts; i++) {
> kfree(tr->topts[i].topts);
> }
> @@ -10740,6 +10751,7 @@ __init static void enable_instances(void)
> bool traceoff = false;
> char *flag_delim;
> char *addr_delim;
> + char *rname __free(kfree) = NULL;
>
> tok = strsep(&curr_str, ",");
>
> @@ -10796,6 +10808,7 @@ __init static void enable_instances(void)
> pr_warn("Failed to map boot instance %s to %s\n", name, tok);
> continue;
> }
> + rname = kstrdup(tok, GFP_KERNEL);
> }
>
> if (start) {
> @@ -10832,7 +10845,7 @@ __init static void enable_instances(void)
> */
> if (start) {
> tr->flags |= TRACE_ARRAY_FL_BOOT | TRACE_ARRAY_FL_LAST_BOOT;
> - tr->ref++;
> + tr->range_name = no_free_ptr(rname);
> }
>
> while ((tok = strsep(&curr_str, ","))) {
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 47c0742fe9ec..ae8f7fac6592 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -348,6 +348,7 @@ struct trace_array {
> unsigned int mapped;
> unsigned long range_addr_start;
> unsigned long range_addr_size;
> + char *range_name;
> long text_delta;
> int nr_modules;
> long *module_delta;