linux-kernel - Re: [PATCH v2] ftrace: Introduce PERMANENT ftrace

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Date:   Mon, 14 Oct 2019 11:17:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     mingo@...hat.com, jpoimboe@...hat.com, jikos@...nel.org,
        pmladek@...e.com, joe.lawrence@...hat.com,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: [PATCH v2] ftrace: Introduce PERMANENT ftrace_ops flag

On Mon, 14 Oct 2019 12:59:23 +0200
Miroslav Benes <mbenes@...e.cz> wrote:

>  int
>  ftrace_enable_sysctl(struct ctl_table *table, int write,
>  		     void __user *buffer, size_t *lenp,
> @@ -6740,8 +6754,6 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
>  	if (ret || !write || (last_ftrace_enabled == !!ftrace_enabled))
>  		goto out;
>  
> -	last_ftrace_enabled = !!ftrace_enabled;
> -
>  	if (ftrace_enabled) {
>  
>  		/* we are starting ftrace again */
> @@ -6752,12 +6764,19 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
>  		ftrace_startup_sysctl();
>  
>  	} else {
> +		if (is_permanent_ops_registered()) {
> +			ftrace_enabled = last_ftrace_enabled;

Although this is not incorrect, but may be somewhat confusing.

At this location, last_ftrace_enabled is always true.

I'm thinking this would be better to simply set it to false here.


> +			ret = -EBUSY;
> +			goto out;
> +		}
> +
>  		/* stopping ftrace calls (just send to ftrace_stub) */
>  		ftrace_trace_function = ftrace_stub;
>  
>  		ftrace_shutdown_sysctl();
>  	}
>  
> +	last_ftrace_enabled = !!ftrace_enabled;
>   out:

And move the assignment of last_ftrace_enabled to after the "out:"
label.

-- Steve

>  	mutex_unlock(&ftrace_lock);
>  	return ret;