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watchdog: core: make sure the watchdog worker always works 

When running a command like 'chrt -f 50 dd if=/dev/zero of=/dev/null',
the watchdog_worker fails to service the HW watchdog and the
HW watchdog fires long before the watchdog soft timeout.

At the moment, the watchdog_worker is invoked as a delayed work.
Delayed works are handled by non realtime kernel threads. The
WQ_HIGHPRI flag only increases the niceness of that threads.

This patch replaces the delayed work logic by kthread delayed work,
and sets the associated kernel task to SCHED_FIFO with the highest
priority, in order to ensure that the watchdog worker will run as
soon as possible.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
This commit is contained in:
Christophe Leroy 2017-12-08 11:18:35 +01:00 committed by Wim Van Sebroeck
parent 71d1f05884
commit 38a1222ae4
1 changed files with 27 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
drivers/watchdog/watchdog_dev.c
View File

@ -39,6 +39,7 @@
#include <linux/jiffies.h> /* For timeout functions */
#include <linux/kernel.h> /* For printk/panic/... */
#include <linux/kref.h> /* For data references */
#include <linux/kthread.h> /* For kthread_delayed_work */
#include <linux/miscdevice.h> /* For handling misc devices */
#include <linux/module.h> /* For module stuff/... */
#include <linux/mutex.h> /* For mutexes */
@ -46,9 +47,10 @@
#include <linux/slab.h> /* For memory functions */
#include <linux/types.h> /* For standard types (like size_t) */
#include <linux/watchdog.h> /* For watchdog specific items */
#include <linux/workqueue.h> /* For workqueue */
#include <linux/uaccess.h> /* For copy_to_user/put_user/... */
#include <uapi/linux/sched/types.h> /* For struct sched_param */
#include "watchdog_core.h"
#include "watchdog_pretimeout.h"
@ -67,7 +69,7 @@ struct watchdog_core_data {
struct mutex lock;
unsigned long last_keepalive;
unsigned long last_hw_keepalive;
struct delayed_work work;
struct kthread_delayed_work work;
unsigned long status; /* Internal status bits */
#define _WDOG_DEV_OPEN 0 /* Opened ? */
#define _WDOG_ALLOW_RELEASE 1 /* Did we receive the magic char ? */
@ -79,7 +81,7 @@ static dev_t watchdog_devt;
/* Reference to watchdog device behind /dev/watchdog */
static struct watchdog_core_data *old_wd_data;
static struct workqueue_struct *watchdog_wq;
static struct kthread_worker *watchdog_kworker;
static bool handle_boot_enabled =
IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED);
@ -140,9 +142,10 @@ static inline void watchdog_update_worker(struct watchdog_device *wdd)
long t = watchdog_next_keepalive(wdd);
if (t > 0)
mod_delayed_work(watchdog_wq, &wd_data->work, t);
kthread_mod_delayed_work(watchdog_kworker,
&wd_data->work, t);
} else {
cancel_delayed_work(&wd_data->work);
kthread_cancel_delayed_work_sync(&wd_data->work);
}
}
@ -154,8 +157,8 @@ static int __watchdog_ping(struct watchdog_device *wdd)
int err;
if (time_is_after_jiffies(earliest_keepalive)) {
mod_delayed_work(watchdog_wq, &wd_data->work,
earliest_keepalive - jiffies);
kthread_mod_delayed_work(watchdog_kworker, &wd_data->work,
earliest_keepalive - jiffies);
return 0;
}
@ -203,12 +206,13 @@ static bool watchdog_worker_should_ping(struct watchdog_core_data *wd_data)
return wdd && (watchdog_active(wdd) || watchdog_hw_running(wdd));
}
static void watchdog_ping_work(struct work_struct *work)
static void watchdog_ping_work(struct kthread_work *work)
{
struct watchdog_core_data *wd_data;
wd_data = container_of(to_delayed_work(work), struct watchdog_core_data,
work);
wd_data = container_of(container_of(work, struct kthread_delayed_work,
work),
struct watchdog_core_data, work);
mutex_lock(&wd_data->lock);
if (watchdog_worker_should_ping(wd_data))
@ -921,10 +925,10 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
wd_data->wdd = wdd;
wdd->wd_data = wd_data;
if (!watchdog_wq)
if (IS_ERR_OR_NULL(watchdog_kworker))
return -ENODEV;
INIT_DELAYED_WORK(&wd_data->work, watchdog_ping_work);
kthread_init_delayed_work(&wd_data->work, watchdog_ping_work);
if (wdd->id == 0) {
old_wd_data = wd_data;
@ -970,7 +974,8 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
__module_get(wdd->ops->owner);
kref_get(&wd_data->kref);
if (handle_boot_enabled)
queue_delayed_work(watchdog_wq, &wd_data->work, 0);
kthread_queue_delayed_work(watchdog_kworker,
&wd_data->work, 0);
else
pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n",
wdd->id);
@ -1007,7 +1012,7 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
watchdog_stop(wdd);
}
cancel_delayed_work_sync(&wd_data->work);
kthread_cancel_delayed_work_sync(&wd_data->work);
kref_put(&wd_data->kref, watchdog_core_data_release);
}
@ -1111,13 +1116,14 @@ void watchdog_dev_unregister(struct watchdog_device *wdd)
int __init watchdog_dev_init(void)
{
int err;
struct sched_param param = {.sched_priority = MAX_RT_PRIO - 1,};
watchdog_wq = alloc_workqueue("watchdogd",
WQ_HIGHPRI | WQ_MEM_RECLAIM, 0);
if (!watchdog_wq) {
pr_err("Failed to create watchdog workqueue\n");
return -ENOMEM;
watchdog_kworker = kthread_create_worker(0, "watchdogd");
if (IS_ERR(watchdog_kworker)) {
pr_err("Failed to create watchdog kworker\n");
return PTR_ERR(watchdog_kworker);
}
sched_setscheduler(watchdog_kworker->task, SCHED_FIFO, &param);
err = class_register(&watchdog_class);
if (err < 0) {
@ -1136,7 +1142,7 @@ int __init watchdog_dev_init(void)
err_alloc:
class_unregister(&watchdog_class);
err_register:
destroy_workqueue(watchdog_wq);
kthread_destroy_worker(watchdog_kworker);
return err;
}
@ -1150,7 +1156,7 @@ void __exit watchdog_dev_exit(void)
{
unregister_chrdev_region(watchdog_devt, MAX_DOGS);
class_unregister(&watchdog_class);
destroy_workqueue(watchdog_wq);
kthread_destroy_worker(watchdog_kworker);
}
module_param(handle_boot_enabled, bool, 0444);