Re: [RFC PATCH] ftrace: speed up module enable by binary searching module symbols

[Google]

Hi,

On Wed, 16 Sep 2026 16:27:15 +0800, Yaxiong Tian <tianyaxiong@xxxxxxxxxx> wrote:

> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -8010,11 +8011,137 @@ void ftrace_release_mod(struct module *mod)
> +
> +	/* mod->kallsyms is not replaced until do_init_module() returns. */
> +	rcu_read_lock();
> +	kallsyms = rcu_dereference(mod->kallsyms);

Consider using rcu_access_pointer(mod->kallsyms) or
rcu_dereference_raw(mod->kallsyms) rather than a transient
rcu_read_lock()/rcu_read_unlock() pair.

> +	rcu_read_unlock();
> +
> +	if (!kallsyms || kallsyms->num_symtab < 2)
> [...]
> +	 * ftrace never came up, where the loop below would not run anyway; that
> +	 * also makes reading ftrace_disabled without the lock safe.
> +	 */
> +	syms = ftrace_disabled ? NULL : ftrace_mod_syms_alloc(mod);

Because ftrace_disabled is one-way flag, if you find ftrace_disabled here,
you can return from this function soon.

Thanks,

> +
>  	mutex_lock(&ftrace_lock);
>  

-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>