Re: [PATCH] ftrace: fix recursive locking direct_mutex in ftrace_modify_direct_caller

[Steven Rostedt]

On Mon, 19 Sep 2022 10:29:55 -0700
Song Liu <song@xxxxxxxxxx> wrote:

> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 439e2ab6905e..d308d0674805 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5461,7 +5461,7 @@ int __weak ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
>  	if (ret)
>  		goto out_lock;
>  
> -	ret = register_ftrace_function(&stub_ops);
> +	ret = register_ftrace_function_nolock(&stub_ops);
>  	if (ret) {
>  		ftrace_set_filter_ip(&stub_ops, ip, 1, 0);
>  		goto out_lock;
> -- 

We need to update the comments to this function, as well add an:

#define lock_direct_assert_held()	lockdep_assert_held(&direct_mutex);

And call that in this function. Otherwise, we can be calling this code
without it held and cause races.

-- Steve