function_graph: Restore direct mode when callbacks drop to one

function_graph: Restore direct mode when callbacks drop to one

[ 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>