fail_function: Remove a redundant mutex unlock

Fix a mutex_unlock() issue where before copy_from_user() is
not called mutex_locked.

Fixes: 4b1a29a ("error-injection: Support fault injection framework")
Reported-by: Hulk Robot <[email protected]>
Signed-off-by: Luo Meng <[email protected]>
Signed-off-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
Acked-by: Masami Hiramatsu <[email protected]>
Link: https://lore.kernel.org/bpf/160570737118.263807.8358435412898356284.stgit@devnote2

Author: Luo Meng

kernel/fail_function.c

@@ -253,7 +253,7 @@ static ssize_t fei_write(struct file *file, const char __user *buffer,
 
 	if (copy_from_user(buf, buffer, count)) {
 		ret = -EFAULT;
-		goto out;
+		goto out_free;
 	}
 	buf[count] = '\0';
 	sym = strstrip(buf);
@@ -307,8 +307,9 @@ static ssize_t fei_write(struct file *file, const char __user *buffer,
 		ret = count;
 	}
 out:
-	kfree(buf);
 	mutex_unlock(&fei_lock);
+out_free:
+	kfree(buf);
 	return ret;
 }