Re: [PATCH 6.18.y] fgraph: Fix thresh_return nosleeptime double-adjust

[Greg KH <greg@kroah.com>]

On Wed, Mar 18, 2026 at 09:13:53AM -0400, Sasha Levin wrote:
> From: Shengming Hu <hu.shengming@zte.com.cn>
> 
> [ Upstream commit b96d0c59cdbb2a22b2545f6f3d5c6276b05761dd ]
> 
> 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.
> 
> Cc: stable@vger.kernel.org
> Link: https://patch.msgid.link/20260221113314048jE4VRwIyZEALiYByGK0My@zte.com.cn
> Fixes: 3c9880f3ab52b ("ftrace: Use a running sleeptime instead of saving on shadow stack")
> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Signed-off-by: Shengming Hu <hu.shengming@zte.com.cn>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  kernel/trace/trace_functions_graph.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index a7f4b9a47a71a..0e65d1f452657 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -378,9 +378,14 @@ static void trace_graph_thresh_return(struct ftrace_graph_ret *trace,
>  				      struct fgraph_ops *gops,
>  				      struct ftrace_regs *fregs)
>  {
> +	struct trace_array *tr = gops->private;
>  	struct fgraph_times *ftimes;
> +	unsigned int trace_ctx;
> +	u64 calltime, rettime;
>  	int size;
>  
> +	rettime = trace_clock_local();
> +
>  	ftrace_graph_addr_finish(gops, trace);
>  
>  	if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT)) {
> @@ -394,11 +399,13 @@ static void trace_graph_thresh_return(struct ftrace_graph_ret *trace,
>  
>  	handle_nosleeptime(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 = {
> -- 
> 2.51.0
> 
> 

Does not apply to the tree :(