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

[hu.shengming]

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.

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