[PATCH 6.18 712/752] function_graph: Restore direct mode when callbacks drop to one

Sasha Levin
2026-02-28T17:58:50Z

From: Shengming Hu <hu.shengming@zte.com.cn>

[ Upstream commit 53b2fae90ff01fede6520ca744ed5e8e366497ba ]

When registering a second fgraph callback, direct path is disabled and
array loop is used instead. When ftrace_graph_active falls back to one,
we try to re-enable direct mode via ftrace_graph_enable_direct(true, ...).
But ftrace_graph_enable_direct() incorrectly disables the static key
rather than enabling it. This leaves fgraph_do_direct permanently off
after first multi-callback transition, so direct fast mode is never
restored.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260213142932519cuWSpEXeS4-UnCvNXnK2P@zte.com.cn
Fixes: cc60ee813b503 ("function_graph: Use static_call and branch to optimize entry function")
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/fgraph.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 599f2939cd940..13832ff06c96c 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -1311,7 +1311,7 @@ static void ftrace_graph_enable_direct(bool enable_branch, struct fgraph_ops *go
static_call_update(fgraph_func, func);
static_call_update(fgraph_retfunc, retfunc);
if (enable_branch)
- static_branch_disable(&fgraph_do_direct);
+ static_branch_enable(&fgraph_do_direct);
}

static void ftrace_graph_disable_direct(bool disable_branch)
--
2.51.0