fgraph: Fix missing unlock in register_ftrace_graph()

Use guard(mutex)() to acquire and automatically release ftrace_lock,
fixing the issue of not unlocking when calling cpuhp_setup_state()
fails.

Fixes smatch warning:

kernel/trace/fgraph.c:1317 register_ftrace_graph() warn: inconsistent returns '&ftrace_lock'.

Link: https://lore.kernel.org/20241024155917.1019580-1-lihuafei1@huawei.com
Fixes: 2c02f7375e65 ("fgraph: Use CPU hotplug mechanism to initialize idle shadow stacks")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202410220121.wxg0olfd-lkp@intel.com/
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Li Huafei <lihuafei1@huawei.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 41e7a15dcb50c4bf99a1620ddae7ba0562aa95ca..cd1c2946018c876d01c07f63f540cbb245733577 100644 (file)
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -1252,7 +1252,7 @@ int register_ftrace_graph(struct fgraph_ops *gops)
        int ret = 0;
        int i = -1;
 
-       mutex_lock(&ftrace_lock);
+       guard(mutex)(&ftrace_lock);
 
        if (!fgraph_initialized) {
                ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "fgraph_idle_init",
@@ -1273,10 +1273,8 @@ int register_ftrace_graph(struct fgraph_ops *gops)
        }
 
        i = fgraph_lru_alloc_index();
-       if (i < 0 || WARN_ON_ONCE(fgraph_array[i] != &fgraph_stub)) {
-               ret = -ENOSPC;
-               goto out;
-       }
+       if (i < 0 || WARN_ON_ONCE(fgraph_array[i] != &fgraph_stub))
+               return -ENOSPC;
        gops->idx = i;
 
        ftrace_graph_active++;
@@ -1313,8 +1311,6 @@ error:
                gops->saved_func = NULL;
                fgraph_lru_release_index(i);
        }
-out:
-       mutex_unlock(&ftrace_lock);
        return ret;
 }