[PATCH CSDlock 1/4] locking/csd_lock: Add Kconfig option for csd_debug default

["Paul E. McKenney" <paulmck@kernel.org>]

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>
Cc: Juergen Gross <jgross@suse.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 6 ++++--
 kernel/smp.c                                    | 2 +-
 lib/Kconfig.debug                               | 9 +++++++++
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6221a1d057dd..ce70777f5999 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/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)
diff --git a/kernel/smp.c b/kernel/smp.c
index 06a413987a14..e2d558f5cef8 100644
--- a/kernel/smp.c
+++ b/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)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c8b379e2e9ad..e1b160a0474d 100644
--- a/lib/Kconfig.debug
+++ b/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
-- 
2.40.0.rc2