linux-kernel - [PATCH 2/2] sparc: Implement update_arch_nmi

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Date:   Thu,  6 Oct 2016 15:16:43 -0700
From:   Babu Moger <babu.moger@...cle.com>
To:     mingo@...nel.org, akpm@...ux-foundation.org, ak@...ux.intel.com,
        jkosina@...e.cz, baiyaowei@...s.chinamobile.com,
        dzickus@...hat.com, atomlin@...hat.com, uobergfe@...hat.com,
        tj@...nel.org, hidehiro.kawai.ez@...achi.com, johunt@...mai.com,
        davem@...emloft.net, sparclinux@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, babu.moger@...cle.com
Subject: [PATCH 2/2] sparc: Implement update_arch_nmi_watchdog

Implement function update_arch_nmi_watchdog to enable/disable
nmi watchdog. Sparc uses arch specific nmi watchdog handler.
Currently, we do not have a way to enable/disable nmi watchdog
dynamically. With these patches we can enable or disable arch
specinf nmi watchdogs using proc or sysctl interface.

Example commands.
To enable: echo 1 >  /proc/sys/kernel/nmi_watchdog
To disable: echo 0 >  /proc/sys/kernel/nmi_watchdog

It can also achieved using the sysctl parameter kernel.nmi_watchdog

Signed-off-by: Babu Moger <babu.moger@...cle.com>
---
 arch/sparc/kernel/nmi.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/arch/sparc/kernel/nmi.c b/arch/sparc/kernel/nmi.c
index a9973bb..27c4e18 100644
--- a/arch/sparc/kernel/nmi.c
+++ b/arch/sparc/kernel/nmi.c
@@ -153,6 +153,8 @@ static void report_broken_nmi(int cpu, int *prev_nmi_count)
 
 void stop_nmi_watchdog(void *unused)
 {
+	if (!__this_cpu_read(wd_enabled))
+		return;
 	pcr_ops->write_pcr(0, pcr_ops->pcr_nmi_disable);
 	__this_cpu_write(wd_enabled, 0);
 	atomic_dec(&nmi_active);
@@ -207,6 +209,8 @@ error:
 
 void start_nmi_watchdog(void *unused)
 {
+	if (__this_cpu_read(wd_enabled))
+		return;
 	__this_cpu_write(wd_enabled, 1);
 	atomic_inc(&nmi_active);
 
@@ -270,3 +274,25 @@ static int __init setup_nmi_watchdog(char *str)
 	return 0;
 }
 __setup("nmi_watchdog=", setup_nmi_watchdog);
+
+#ifdef CONFIG_LOCKUP_DETECTOR
+void update_arch_nmi_watchdog(void)
+{
+	if (atomic_read(&nmi_active) < 0) {
+		printk(KERN_WARNING
+		       "NMI watchdog cannot be enabled or disabled\n");
+		return;
+	}
+
+	/*
+	 * Check for bit 0. Bit 0 is dedicated for hard lockup detector or
+	 * arch specific nmi and bit 1 for the soft lockup detector. We
+	 * are interested only in bit 0 here.
+	 */
+	if (watchdog_enabled & 1)
+		on_each_cpu(start_nmi_watchdog, NULL, 1);
+	else
+		on_each_cpu(stop_nmi_watchdog, NULL, 1);
+
+}
+#endif
-- 
1.7.1