linux-kernel - Re: [PATCH RFC ftrace] Asynchronous grace period for register_ftrace

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Message-ID: <20240403152912.7f03c6db@gandalf.local.home>
Date: Wed, 3 Apr 2024 15:29:12 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org, Masami
 Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Jakub Kicinski
 <kuba@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Chris Mason
 <clm@...com>
Subject: Re: [PATCH RFC ftrace] Asynchronous grace period for
 register_ftrace_direct()

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