linux-kernel - Re: [PATCH] fgraph: Keep track of when fgraph

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Message-Id: <20250619124517.3e6665439e1794918e83f1b6@kernel.org>
Date: Thu, 19 Jun 2025 12:45:17 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] fgraph: Keep track of when fgraph_ops are registered or
 not

On Wed, 18 Jun 2025 07:31:17 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> Add a warning if unregister_ftrace_graph() is called without ever
> registering it, or if register_ftrace_graph() is called twice. This can
> detect errors when they happen and not later when there's a side effect:
> 
> Link: https://lore.kernel.org/all/20250617120830.24fbdd62@gandalf.local.home/
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/fgraph.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index c5b207992fb4..c6bb6c68764f 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -1325,6 +1325,10 @@ int register_ftrace_graph(struct fgraph_ops *gops)
>  	int ret = 0;
>  	int i = -1;
>  
> +	if (WARN_ONCE(gops->ops.flags & FTRACE_OPS_FL_GRAPH,
> +		      "function graph ops registered again"))
> +		return -EBUSY;
> +
>  	guard(mutex)(&ftrace_lock);
>  
>  	if (!fgraph_stack_cachep) {
> @@ -1401,17 +1405,21 @@ void unregister_ftrace_graph(struct fgraph_ops *gops)
>  {
>  	int command = 0;
>  
> +	if (WARN_ONCE(!(gops->ops.flags & FTRACE_OPS_FL_GRAPH),
> +		      "function graph ops unregistered without registering"))
> +		return;
> +
>  	guard(mutex)(&ftrace_lock);
>  
>  	if (unlikely(!ftrace_graph_active))
> -		return;
> +		goto out;
>  
>  	if (unlikely(gops->idx < 0 || gops->idx >= FGRAPH_ARRAY_SIZE ||
>  		     fgraph_array[gops->idx] != gops))
> -		return;
> +		goto out;
>  
>  	if (fgraph_lru_release_index(gops->idx) < 0)
> -		return;
> +		goto out;
>  
>  	fgraph_array[gops->idx] = &fgraph_stub;
>  
> @@ -1434,4 +1442,6 @@ void unregister_ftrace_graph(struct fgraph_ops *gops)
>  		unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
>  	}
>  	gops->saved_func = NULL;
> + out:
> +	gops->ops.flags = 0;

Can we make it cleaning only FTRACE_OPS_FL_GRAPH flag here?
Or, ops.flags should be set again before registering it?

Thank you,

>  }
> -- 
> 2.47.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>