signal: move show_unhandled_signals sysctl to its own file

The show_unhandled_signals sysctl is the only sysctl for debug
left on kernel/sysctl.c. We've been moving the syctls out from
kernel/sysctl.c so to help avoid merge conflicts as the shared
array gets out of hand.

This change incurs simplifies sysctl registration by localizing
it where it should go for a penalty in size of increasing the
kernel by 23 bytes, we accept this given recent cleanups have
actually already saved us 1465 bytes in the prior commits.

./scripts/bloat-o-meter vmlinux.3-remove-dev-table vmlinux.4-remove-debug-table
add/remove: 3/1 grow/shrink: 0/1 up/down: 177/-154 (23)
Function                                     old     new   delta
signal_debug_table                             -     128    +128
init_signal_sysctls                            -      33     +33
__pfx_init_signal_sysctls                      -      16     +16
sysctl_init_bases                             85      59     -26
debug_table                                  128       -    -128
Total: Before=21256967, After=21256990, chg +0.00%

Reviewed-by: Joel Granados <j.granados@samsung.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

kernel/signal.c

@@ -45,6 +45,7 @@
 #include <linux/posix-timers.h>
 #include <linux/cgroup.h>
 #include <linux/audit.h>
+#include <linux/sysctl.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/signal.h>
@@ -4771,6 +4772,28 @@ static inline void siginfo_buildtime_checks(void)
 #endif
 }
 
+#if defined(CONFIG_SYSCTL)
+static struct ctl_table signal_debug_table[] = {
+#ifdef CONFIG_SYSCTL_EXCEPTION_TRACE
+	{
+		.procname	= "exception-trace",
+		.data		= &show_unhandled_signals,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec
+	},
+#endif
+	{ }
+};
+
+static int __init init_signal_sysctls(void)
+{
+	register_sysctl_init("debug", signal_debug_table);
+	return 0;
+}
+early_initcall(init_signal_sysctls);
+#endif /* CONFIG_SYSCTL */
+
 void __init signals_init(void)
 {
 	siginfo_buildtime_checks();

kernel/sysctl.c

@@ -2319,19 +2319,6 @@ static struct ctl_table vm_table[] = {
 	{ }
 };
 
-static struct ctl_table debug_table[] = {
-#ifdef CONFIG_SYSCTL_EXCEPTION_TRACE
-	{
-		.procname	= "exception-trace",
-		.data		= &show_unhandled_signals,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec
-	},
-#endif
-	{ }
-};
-
 int __init sysctl_init_bases(void)
 {
 	register_sysctl_init("kernel", kern_table);
@@ -2341,7 +2328,6 @@ int __init sysctl_init_bases(void)
 #endif
 
 	register_sysctl_init("vm", vm_table);
-	register_sysctl_init("debug", debug_table);
 
 	return 0;
 }