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sched: Ensure watchdog is enabled before disabling

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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>
This commit is contained in:
Olav Haugan 2016-11-03 15:10:57 -07:00
parent 34a3cdf14e
commit af04b3a2ba
3 changed files with 45 additions and 8 deletions
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9
include/linux/sched.h
View file

@ -446,6 +446,7 @@ extern unsigned int hardlockup_panic;
void lockup_detector_init(void);
extern void watchdog_enable(unsigned int cpu);
extern void watchdog_disable(unsigned int cpu);
extern bool watchdog_configured(unsigned int cpu);
#else
static inline void touch_softlockup_watchdog_sched(void)
{
@ -468,6 +469,14 @@ static inline void watchdog_enable(unsigned int cpu)
static inline void watchdog_disable(unsigned int cpu)
{
}
static inline bool watchdog_configured(unsigned int cpu)
{
/*
* Predend the watchdog is always configured.
* We will be waiting for the watchdog to be enabled in core isolation
*/
return true;
}
#endif
#ifdef CONFIG_DETECT_HUNG_TASK

16
kernel/sched/core.c
View file

@ -5704,6 +5704,22 @@ int sched_isolate_cpu(int cpu)
if (++cpu_isolation_vote[cpu] > 1)
goto out;
/*
* 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.
*/
if (!watchdog_configured(cpu)) {
msleep(20);
if (!watchdog_configured(cpu)) {
--cpu_isolation_vote[cpu];
ret_code = -EBUSY;
goto out;
}
}
set_cpu_isolated(cpu, true);
cpumask_clear_cpu(cpu, &avail_cpus);

28
kernel/watchdog.c
View file

@ -588,17 +588,13 @@ static void watchdog_set_prio(unsigned int policy, unsigned int prio)
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);
@ -614,24 +610,40 @@ void watchdog_enable(unsigned int cpu)
/* 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)