[PATCH v2] fgraph: Fix missing unlock in register_ftrace_graph()

[Li Huafei]

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'.

Fixes: 2c02f7375e65 ("fgraph: Use CPU hotplug mechanism to initialize idle shadow stacks")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Closes: https://lore.kernel.org/r/202410220121.wxg0olfd-lkp@xxxxxxxxx/
Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
---
Changes in v2:
 - Use guard() to acquire and automatically release ftrace_lock.
---
 kernel/trace/fgraph.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 41e7a15dcb50..cd1c2946018c 100644
--- 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 @@ int register_ftrace_graph(struct fgraph_ops *gops)
 		gops->saved_func = NULL;
 		fgraph_lru_release_index(i);
 	}
-out:
-	mutex_unlock(&ftrace_lock);
 	return ret;
 }
 
-- 
2.25.1