linux-kernel - Re: [PATCH 5/5] ftrace: Use guard to take ftrace_lock in ftrace_graph_set

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Message-ID: <20241028091656.GJ9767@noisy.programming.kicks-ass.net>
Date: Mon, 28 Oct 2024 10:16:56 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 5/5] ftrace: Use guard to take ftrace_lock in
 ftrace_graph_set_hash()

On Mon, Oct 28, 2024 at 03:12:33AM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@...dmis.org>
> 
> The ftrace_lock is taken for most of the ftrace_graph_set_hash() function
> throughout the end. Use guard to take the ftrace_lock to simplify the exit
> paths.
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/ftrace.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index c0fabd7da5b2..b4ef469f4fd2 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6816,12 +6816,10 @@ ftrace_graph_set_hash(struct ftrace_hash *hash, char *buffer)
>  
>  	func_g.len = strlen(func_g.search);
>  
> -	mutex_lock(&ftrace_lock);
> +	guard(mutex)(&ftrace_lock);
>  
> -	if (unlikely(ftrace_disabled)) {
> -		mutex_unlock(&ftrace_lock);
> +	if (unlikely(ftrace_disabled))
>  		return -ENODEV;
> -	}
>  
>  	do_for_each_ftrace_rec(pg, rec) {
>  
> @@ -6837,7 +6835,7 @@ ftrace_graph_set_hash(struct ftrace_hash *hash, char *buffer)
>  				if (entry)
>  					continue;
>  				if (add_hash_entry(hash, rec->ip) == NULL)
> -					goto out;
> +					return 0;
>  			} else {
>  				if (entry) {
>  					free_hash_entry(hash, entry);
> @@ -6846,13 +6844,8 @@ ftrace_graph_set_hash(struct ftrace_hash *hash, char *buffer)
>  			}
>  		}
>  	} while_for_each_ftrace_rec();
> -out:
> -	mutex_unlock(&ftrace_lock);
>  
> -	if (fail)
> -		return -EINVAL;
> -
> -	return 0;
> +	return fail ? -EINVAL : 0;
>  }

Isn't the fail case more a case of -ESRCH / -ENOENT rather than -EINVAL?

Anyway, that's orthogonal, the patch preserves existing semantics and
looks okay (as do the others fwiw).