Re: [PATCH RFC ftrace] Asynchronous grace period for register_ftrace_direct()

[Steven Rostedt]

On Wed, 3 Apr 2024 11:53:14 -0700
"Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote:

> @@ -5366,6 +5366,13 @@ static void remove_direct_functions_hash(struct ftrace_hash *hash, unsigned long
>  	}
>  }
>  
> +static void register_ftrace_direct_cb(struct rcu_head *rhp)
> +{
> +	struct ftrace_hash *fhp = container_of(rhp, struct ftrace_hash, rcu);
> +
> +	free_ftrace_hash(fhp);
> +}
> +
>  /**
>   * register_ftrace_direct - Call a custom trampoline directly
>   * for multiple functions registered in @ops
> @@ -5464,10 +5471,8 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
>   out_unlock:
>  	mutex_unlock(&direct_mutex);
>  
> -	if (free_hash && free_hash != EMPTY_HASH) {
> -		synchronize_rcu_tasks();
> -		free_ftrace_hash(free_hash);
> -	}
> +	if (free_hash && free_hash != EMPTY_HASH)
> +		call_rcu_tasks(&free_hash->rcu, register_ftrace_direct_cb);
>  
>  	if (new_hash)
>  		free_ftrace_hash(new_hash);

I'm getting ready to go on PTO, but a quick glance doesn't look like this
would cause any harm.

-- Steve