locking/csd_lock: Add Kconfig option for csd_debug default

The csd_debug kernel parameter works well, but is inconvenient in cases
where it is more closely associated with boot loaders or automation than
with a particular kernel version or release.  Thererfore, provide a new
CSD_LOCK_WAIT_DEBUG_DEFAULT Kconfig option that defaults csd_debug to
1 when selected and 0 otherwise, with this latter being the default.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20230321005516.50558-1-paulmck@kernel.org

Author: paulmckrcu

Documentation/admin-guide/kernel-parameters.txt

@@ -893,8 +893,10 @@
 			handling. When switched on, additional debug data is
 			printed to the console in case a hanging CPU is
 			detected, and that CPU is pinged again in order to try
-			to resolve the hang situation.
-			0: disable csdlock debugging (default)
+			to resolve the hang situation.  The default value of
+			this option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
+			Kconfig option.
+			0: disable csdlock debugging
 			1: enable basic csdlock debugging (minor impact)
 			ext: enable extended csdlock debugging (more impact,
 			     but more data)

kernel/smp.c

@@ -158,7 +158,7 @@ void __init call_function_init(void)
 
 #ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
 
-static DEFINE_STATIC_KEY_FALSE(csdlock_debug_enabled);
+static DEFINE_STATIC_KEY_MAYBE(CONFIG_CSD_LOCK_WAIT_DEBUG_DEFAULT, csdlock_debug_enabled);
 static DEFINE_STATIC_KEY_FALSE(csdlock_debug_extended);
 
 static int __init csdlock_debug(char *str)

lib/Kconfig.debug

@@ -1480,6 +1480,15 @@ config CSD_LOCK_WAIT_DEBUG
 	  include the IPI handler function currently executing (if any)
 	  and relevant stack traces.
 
+config CSD_LOCK_WAIT_DEBUG_DEFAULT
+	bool "Default csd_lock_wait() debugging on at boot time"
+	depends on CSD_LOCK_WAIT_DEBUG
+	depends on 64BIT
+	default n
+	help
+	  This option causes the csdlock_debug= kernel boot parameter to
+	  default to 1 (basic debugging) instead of 0 (no debugging).
+
 endmenu # lock debugging
 
 config TRACE_IRQFLAGS