Re: [PATCH 2/2] fgraph: fix thresh_return nosleeptime double-adjust

[Google]

On Sat, 21 Feb 2026 11:33:14 +0800 (CST)
<hu.shengming@xxxxxxxxxx> wrote:

> From: Shengming Hu <hu.shengming@xxxxxxxxxx>
> 
> trace_graph_thresh_return() called handle_nosleeptime() and then
> delegated to trace_graph_return(), which calls
> handle_nosleeptime() again. When sleep-time accounting is
> disabled this double-adjusts calltime and can produce bogus
> durations (including underflow).
> 
> Fix this by computing rettime once, applying
> handle_nosleeptime() only once, using the adjusted calltime
> for threshold comparison, and writing the return event
> directly via __trace_graph_return() when the threshold is met.
> 

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Thanks!

> Fixes: 3c9880f3ab52b ("ftrace: Use a running sleeptime instead of
> saving on shadow stack")
> Signed-off-by: Shengming Hu <hu.shengming@xxxxxxxxxx>
> ---
>  kernel/trace/trace_functions_graph.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index cbe43680c..b9c81fbd9 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -403,8 +403,12 @@ static void trace_graph_thresh_return(struct ftrace_graph_ret *trace,
>  	unsigned long *task_var = fgraph_get_task_var(gops);
>  	struct fgraph_times *ftimes;
>  	struct trace_array *tr;
> +	unsigned int trace_ctx;
> +	u64 calltime, rettime;
>  	int size;
> 
> +	rettime = trace_clock_local();
> +
>  	ftrace_graph_addr_finish(gops, trace);
> 
>  	if (*task_var & TRACE_GRAPH_NOTRACE) {
> @@ -419,11 +423,13 @@ static void trace_graph_thresh_return(struct ftrace_graph_ret *trace,
>  	tr = gops->private;
>  	handle_nosleeptime(tr, trace, ftimes, size);
> 
> -	if (tracing_thresh &&
> -	    (trace_clock_local() - ftimes->calltime < tracing_thresh))
> +	calltime = ftimes->calltime;
> +
> +	if (tracing_thresh && (rettime - calltime < tracing_thresh))
>  		return;
> -	else
> -		trace_graph_return(trace, gops, fregs);
> +
> +	trace_ctx = tracing_gen_ctx();
> +	__trace_graph_return(tr, trace, trace_ctx, calltime, rettime);
>  }
> 
>  static struct fgraph_ops funcgraph_ops = {
> -- 
> 2.25.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>