kernel/smp: Make csdlock_debug= resettable

It is currently possible to set the csdlock_debug_enabled static
branch, but not to reset it.  This is an issue when several different
entities supply kernel boot parameters and also for kernels built with
CONFIG_CSD_LOCK_WAIT_DEBUG_DEFAULT=y.

Therefore, make the csdlock_debug=0 kernel boot parameter turn off
debugging.  Last one wins!

Reported-by: Jes Sorensen <Jes.Sorensen@gmail.com>
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/20230321005516.50558-4-paulmck@kernel.org

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b15198a..5f2ec4b 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -889,12 +889,13 @@
        cs89x0_media=   [HW,NET]
                        Format: { rj45 | aui | bnc }
 
-       csdlock_debug=  [KNL] Enable debug add-ons of cross-CPU function call
-                       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.  The default value of
-                       this option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
+       csdlock_debug=  [KNL] Enable or disable debug add-ons of cross-CPU
+                       function call 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.  The default value of this
+                       option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
                        Kconfig option.
 
        dasd=           [HW,NET]

diff --git a/kernel/smp.c b/kernel/smp.c
index 7a85bcd..298ba75 100644 (file)
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -116,11 +116,16 @@ static DEFINE_STATIC_KEY_MAYBE(CONFIG_CSD_LOCK_WAIT_DEBUG_DEFAULT, csdlock_debug
  */
 static int __init csdlock_debug(char *str)
 {
+       int ret;
        unsigned int val = 0;
 
-       get_option(&str, &val);
-       if (val)
-               static_branch_enable(&csdlock_debug_enabled);
+       ret = get_option(&str, &val);
+       if (ret) {
+               if (val)
+                       static_branch_enable(&csdlock_debug_enabled);
+               else
+                       static_branch_disable(&csdlock_debug_enabled);
+       }
 
        return 1;
 }