linux-kernel - Re: [PATCH 1/2] tracing/wakeup: Balance prolog on fgraph failure

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Message-ID: <20251008112414.03d5d803@gandalf.local.home>
Date: Wed, 8 Oct 2025 11:24:14 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Sasha Levin <sashal@...nel.org>
Cc: mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] tracing/wakeup: Balance prolog on fgraph failure

On Mon,  6 Oct 2025 13:58:47 -0400
Sasha Levin <sashal@...nel.org> wrote:

> diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
> index bf1cb80742aed..fa48bbdf0851c 100644
> --- a/kernel/trace/trace_sched_wakeup.c
> +++ b/kernel/trace/trace_sched_wakeup.c
> @@ -138,8 +138,11 @@ static int wakeup_graph_entry(struct ftrace_graph_ent *trace,
>  		return 0;
>  
>  	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
> -	if (!calltime)
> +	if (!calltime) {
> +		local_dec(&data->disabled);
> +		preempt_enable_notrace();
>  		return 0;
> +	}
>  
>  	*calltime = trace_clock_local();
>  
> @@ -169,8 +172,11 @@ static void wakeup_graph_return(struct ftrace_graph_ret *trace,
>  	rettime = trace_clock_local();
>  
>  	calltime = fgraph_retrieve_data(gops->idx, &size);
> -	if (!calltime)
> +	if (!calltime) {
> +		local_dec(&data->disabled);
> +		preempt_enable_notrace();
>  		return;
> +	}
>  
>  	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
>  	local_dec(&data->disabled);

Technically correct, but this would look better:

diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index bf1cb80742ae..e3f2e4f56faa 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -138,12 +138,10 @@ static int wakeup_graph_entry(struct ftrace_graph_ent *trace,
 		return 0;
 
 	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
-	if (!calltime)
-		return 0;
-
-	*calltime = trace_clock_local();
-
-	ret = __trace_graph_entry(tr, trace, trace_ctx);
+	if (calltime) {
+		*calltime = trace_clock_local();
+		ret = __trace_graph_entry(tr, trace, trace_ctx);
+	}
 	local_dec(&data->disabled);
 	preempt_enable_notrace();
 
@@ -169,12 +167,10 @@ static void wakeup_graph_return(struct ftrace_graph_ret *trace,
 	rettime = trace_clock_local();
 
 	calltime = fgraph_retrieve_data(gops->idx, &size);
-	if (!calltime)
-		return;
+	if (calltime)
+		__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
 
-	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
 	local_dec(&data->disabled);
-
 	preempt_enable_notrace();
 	return;
 }


-- Steve