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Commit 42ea2119 authored by Olav Haugan's avatar Olav Haugan Committed by Pavankumar Kondeti
Browse files

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: default avatarOlav Haugan <ohaugan@codeaurora.org>
[pkondeti@codeaurora.org: resolved minor merge conflicts. Ignored
changes in include/linux/sched.h since they are already present
in include/linux/nmi.h]
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent 2e7ac4ed

kernel/sched/core.c

+17 −0
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ 
#include <linux/security.h>

#include <linux/syscalls.h>

#include <linux/irq.h>

#include <linux/delay.h>



#include <linux/kthread.h>
@@ -5989,6 +5990,22 @@ 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);

kernel/watchdog.c

+20 −8
Original line number Diff line number Diff line
@@ -456,17 +456,13 @@ 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 = this_cpu_ptr(&watchdog_hrtimer);

	unsigned int *enabled = this_cpu_ptr(&watchdog_en);



	lock_device_hotplug_assert();



	if (*enabled)

		return;

	*enabled = 1;



	/*

	 * Start the timer first to prevent the NMI watchdog triggering
@@ -484,19 +480,24 @@ void watchdog_enable(unsigned int cpu) 
		watchdog_nmi_enable(cpu);



	watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);



	/*

	 * 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 = this_cpu_ptr(&watchdog_hrtimer);

	unsigned int *enabled = this_cpu_ptr(&watchdog_en);



	lock_device_hotplug_assert();



	if (!*enabled)

		return;

	*enabled = 0;



	watchdog_set_prio(SCHED_NORMAL, 0);

	/*
@@ -506,6 +507,17 @@ void watchdog_disable(unsigned int cpu) 
	 */

	watchdog_nmi_disable(cpu);

	hrtimer_cancel(hrtimer);



	/*

	 * 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)