commit 11113474ffa0587bf1cf6031c0f80321b109c0c5
author Olav Haugan <ohaugan@codeaurora.org> Thu Nov 03 15:10:57 2016 -0700
committer Syed Rameez Mustafa <rameezmustafa@codeaurora.org> Tue Feb 07 14:51:14 2017 -0800
tree 6cf6129326e5c58599cc10a67b85d2ac8675d123
parent bf6b7fa6455b781c2d86bb4160056f72a9893479

sched: Ensure watchdog is enabled before disabling

There is a race between watchdog being enabled by hotplug and core
isolation disabling the watchdog. When a CPU is hotplugged in and
the hotplug lock has been released the watchdog thread might not
have run yet to enable the watchdog.  We have to wait for the
watchdog to be enabled before proceeding.

Change-Id: I88f73603b6d389a46f8e819d9b490091d5ba4fe9
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>

kernel/watchdog.c

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 3c3898d..f3631a3 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -586,17 +586,13 @@
 	sched_setscheduler(current, policy, &param);
 }
 
-/* Must be called with hotplug lock (lock_device_hotplug()) held. */
 void watchdog_enable(unsigned int cpu)
 {
 	struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 	unsigned int *enabled = raw_cpu_ptr(&watchdog_en);
 
-	lock_device_hotplug_assert();
-
 	if (*enabled)
 		return;
-	*enabled = 1;
 
 	/* kick off the timer for the hardlockup detector */
 	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
@@ -612,24 +608,40 @@
 	/* initialize timestamp */
 	watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 	__touch_watchdog();
+
+	/*
+	 * Need to ensure above operations are observed by other CPUs before
+	 * indicating that timer is enabled. This is to synchronize core
+	 * isolation and hotplug. Core isolation will wait for this flag to be
+	 * set.
+	 */
+	mb();
+	*enabled = 1;
 }
 
-/* Must be called with hotplug lock (lock_device_hotplug()) held. */
 void watchdog_disable(unsigned int cpu)
 {
 	struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 	unsigned int *enabled = raw_cpu_ptr(&watchdog_en);
 
-	lock_device_hotplug_assert();
-
 	if (!*enabled)
 		return;
-	*enabled = 0;
 
 	watchdog_set_prio(SCHED_NORMAL, 0);
 	hrtimer_cancel(hrtimer);
 	/* disable the perf event */
 	watchdog_nmi_disable(cpu);
+
+	/*
+	 * No need for barrier here since disabling the watchdog is
+	 * synchronized with hotplug lock
+	 */
+	*enabled = 0;
+}
+
+bool watchdog_configured(unsigned int cpu)
+{
+	return *per_cpu_ptr(&watchdog_en, cpu);
 }
 
 static void watchdog_cleanup(unsigned int cpu, bool online)