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>

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index eb35700..68bc29e 100644 (file)
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -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);