kcsan, debugfs: Move debugfs file creation out of early init

Commit 56348560 ("debugfs: do not attempt to create a new file
before the filesystem is initalized") forbids creating new debugfs files
until debugfs is fully initialized.  This means that KCSAN's debugfs
file creation, which happened at the end of __init(), no longer works.
And was apparently never supposed to work!

However, there is no reason to create KCSAN's debugfs file so early.
This commit therefore moves its creation to a late_initcall() callback.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: stable <stable@vger.kernel.org>
Fixes: 56348560 ("debugfs: do not attempt to create a new file before the filesystem is initalized")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/kcsan/core.c

@@ -639,8 +639,6 @@ void __init kcsan_init(void)
 
 	BUG_ON(!in_task());
 
-	kcsan_debugfs_init();
-
 	for_each_possible_cpu(cpu)
 		per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles();
 

kernel/kcsan/debugfs.c

@@ -261,7 +261,9 @@ static const struct file_operations debugfs_ops =
 	.release = single_release
 };
 
-void __init kcsan_debugfs_init(void)
+static void __init kcsan_debugfs_init(void)
 {
 	debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
 }
+
+late_initcall(kcsan_debugfs_init);

kernel/kcsan/kcsan.h

@@ -30,11 +30,6 @@ extern bool kcsan_enabled;
 void kcsan_save_irqtrace(struct task_struct *task);
 void kcsan_restore_irqtrace(struct task_struct *task);
 
-/*
- * Initialize debugfs file.
- */
-void kcsan_debugfs_init(void);
-
 /*
  * Statistics counters displayed via debugfs; should only be modified in
  * slow-paths.