On Fri, 28 Aug 2026 08:59:39 -0700
Breno Leitao <[email protected]> wrote:
>
> My LLM came up with something like the following, and it doesn't
> reproduce the problem anymore. Very similar to your code above:
I know the solution but there's subtle things I want to make sure that
works.
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index f9d80c7bd9f16..37845399fe5cf 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -4788,22 +4788,37 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
> static int
> ftrace_filter_open(struct inode *inode, struct file *file)
> {
> - struct ftrace_ops *ops = inode->i_private;
> + struct trace_array *tr = inode->i_private;
> + int ret;
>
> - /* Checks for tracefs lockdown */
> - return ftrace_regex_open(ops,
> - FTRACE_ITER_FILTER | FTRACE_ITER_DO_PROBES,
> - inode, file);
> + /* Checks for tracefs lockdown, and that the instance is still alive */
> + ret = tracing_check_open_get_tr(tr);
> + if (ret)
> + return ret;
> +
> + ret = ftrace_regex_open(tr->ops,
> + FTRACE_ITER_FILTER | FTRACE_ITER_DO_PROBES,
> + inode, file);
> + /* ftrace_regex_open() holds its own reference on success */
> + trace_array_put(tr);
> + return ret;
> }
>
> static int
> ftrace_notrace_open(struct inode *inode, struct file *file)
> {
> - struct ftrace_ops *ops = inode->i_private;
> + struct trace_array *tr = inode->i_private;
> + int ret;
> +
> + /* Checks for tracefs lockdown, and that the instance is still alive */
> + ret = tracing_check_open_get_tr(tr);
> + if (ret)
> + return ret;
>
> - /* Checks for tracefs lockdown */
> - return ftrace_regex_open(ops, FTRACE_ITER_NOTRACE,
> - inode, file);
> + ret = ftrace_regex_open(tr->ops, FTRACE_ITER_NOTRACE, inode, file);
> + /* ftrace_regex_open() holds its own reference on success */
> + trace_array_put(tr);
> + return ret;
> }
>
> /* Type for quick search ftrace basic regexes (globs) from
> filter_parse_regex */
> @@ -7496,11 +7511,15 @@ void ftrace_create_filter_files(struct ftrace_ops
> *ops,
> struct dentry *parent)
> {
>
> + /*
> + * Pass the trace array and not @ops, as @ops is freed when the
> + * instance is removed, but the trace array can still be validated.
> + */
I hate these comments. It's really pointless to state this. It's a "no shit"
comment ;-)
> trace_create_file("set_ftrace_filter", TRACE_MODE_WRITE, parent,
> - ops, &ftrace_filter_fops);
> + ops->private, &ftrace_filter_fops);
But this also assumes that ops->private is always a trace_array. Which may
someday change and we will get a hidden bug if it does.
This is the exact reason I want to look deeper at it.
-- Steve
>
> trace_create_file("set_ftrace_notrace", TRACE_MODE_WRITE, parent,
> - ops, &ftrace_notrace_fops);
> + ops->private, &ftrace_notrace_fops);
> }
>
> /*
