[PATCH 01/10] watchdog/hardlockup: Keep kernel.nmi_watchdog sysctl as 0444 if probe fails

[Douglas Anderson]

The permissions for the kernel.nmi_watchdog sysctl have always been
set at compile time despite the fact that a watchdog can fail to
probe. Let's fix this and set the permissions based on whether the
hardlockup detector actually probed.

Fixes: a994a3147e4c ("watchdog/hardlockup/perf: Implement init time detection of perf")
Reported-by: Petr Mladek <pmladek@xxxxxxxx>
Closes: https://lore.kernel.org/r/ZHCn4hNxFpY5-9Ki@alley
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

 include/linux/nmi.h |  6 ------
 kernel/watchdog.c   | 30 ++++++++++++++++++++----------
 2 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 333465e235e1..3a27169ec383 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -95,12 +95,6 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs);
 static inline void arch_touch_nmi_watchdog(void) { }
 #endif
 
-#if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
-# define NMI_WATCHDOG_SYSCTL_PERM	0644
-#else
-# define NMI_WATCHDOG_SYSCTL_PERM	0444
-#endif
-
 #if defined(CONFIG_HARDLOCKUP_DETECTOR_PERF)
 extern void hardlockup_detector_perf_stop(void);
 extern void hardlockup_detector_perf_restart(void);
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 237990e8d345..4b9e31edb47f 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -880,15 +880,6 @@ static struct ctl_table watchdog_sysctls[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= (void *)&sixty,
 	},
-	{
-		.procname       = "nmi_watchdog",
-		.data		= &watchdog_hardlockup_user_enabled,
-		.maxlen		= sizeof(int),
-		.mode		= NMI_WATCHDOG_SYSCTL_PERM,
-		.proc_handler   = proc_nmi_watchdog,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
-	},
 	{
 		.procname	= "watchdog_cpumask",
 		.data		= &watchdog_cpumask_bits,
@@ -952,10 +943,28 @@ static struct ctl_table watchdog_sysctls[] = {
 	{}
 };
 
+static struct ctl_table watchdog_hardlockup_sysctl[] = {
+	{
+		.procname       = "nmi_watchdog",
+		.data		= &watchdog_hardlockup_user_enabled,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler   = proc_nmi_watchdog,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
+	{}
+};
+
 static void __init watchdog_sysctl_init(void)
 {
 	register_sysctl_init("kernel", watchdog_sysctls);
+
+	if (watchdog_hardlockup_available)
+		watchdog_hardlockup_sysctl[0].mode = 0644;
+	register_sysctl_init("kernel", watchdog_hardlockup_sysctl);
 }
+
 #else
 #define watchdog_sysctl_init() do { } while (0)
 #endif /* CONFIG_SYSCTL */
@@ -1011,6 +1020,8 @@ static int __init lockup_detector_check(void)
 	/* Make sure no work is pending. */
 	flush_work(&detector_work);
 
+	watchdog_sysctl_init();
+
 	return 0;
 
 }
@@ -1030,5 +1041,4 @@ void __init lockup_detector_init(void)
 		allow_lockup_detector_init_retry = true;
 
 	lockup_detector_setup();
-	watchdog_sysctl_init();
 }
-- 
2.41.0.rc0.172.g3f132b7071-goog