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Subject[PATCH] watchdog: core: make sure the watchdog_worker always works
Date
When running a command like 'chrt -f 99 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 patchs replaces the delayed work logic by hrtimer, in order to
ensure that the watchdog_worker will already have priority.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
drivers/watchdog/watchdog_dev.c | 87 +++++++++++++++++++----------------------
1 file changed, 41 insertions(+), 46 deletions(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 1e971a50d7fb..e9b234c4ff67 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -36,7 +36,7 @@
#include <linux/errno.h> /* For the -ENODEV/... values */
#include <linux/fs.h> /* For file operations */
#include <linux/init.h> /* For __init/__exit/... */
-#include <linux/jiffies.h> /* For timeout functions */
+#include <linux/hrtimer.h>
#include <linux/kernel.h> /* For printk/panic/... */
#include <linux/kref.h> /* For data references */
#include <linux/miscdevice.h> /* For handling misc devices */
@@ -46,7 +46,6 @@
#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 "watchdog_core.h"
@@ -65,9 +64,9 @@ struct watchdog_core_data {
struct cdev cdev;
struct watchdog_device *wdd;
struct mutex lock;
- unsigned long last_keepalive;
- unsigned long last_hw_keepalive;
- struct delayed_work work;
+ ktime_t last_keepalive;
+ ktime_t last_hw_keepalive;
+ struct hrtimer timer;
unsigned long status; /* Internal status bits */
#define _WDOG_DEV_OPEN 0 /* Opened ? */
#define _WDOG_ALLOW_RELEASE 1 /* Did we receive the magic char ? */
@@ -79,8 +78,6 @@ 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 bool handle_boot_enabled =
IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED);

@@ -107,18 +104,19 @@ static inline bool watchdog_need_worker(struct watchdog_device *wdd)
(t && !watchdog_active(wdd) && watchdog_hw_running(wdd));
}

-static long watchdog_next_keepalive(struct watchdog_device *wdd)
+static ktime_t watchdog_next_keepalive(struct watchdog_device *wdd)
{
struct watchdog_core_data *wd_data = wdd->wd_data;
unsigned int timeout_ms = wdd->timeout * 1000;
- unsigned long keepalive_interval;
- unsigned long last_heartbeat;
- unsigned long virt_timeout;
+ ktime_t keepalive_interval;
+ ktime_t last_heartbeat, latest_heartbeat;
+ ktime_t virt_timeout;
unsigned int hw_heartbeat_ms;

- virt_timeout = wd_data->last_keepalive + msecs_to_jiffies(timeout_ms);
+ virt_timeout = ktime_add(wd_data->last_keepalive,
+ ms_to_ktime(timeout_ms));
hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
- keepalive_interval = msecs_to_jiffies(hw_heartbeat_ms / 2);
+ keepalive_interval = ms_to_ktime(hw_heartbeat_ms / 2);

if (!watchdog_active(wdd))
return keepalive_interval;
@@ -128,8 +126,11 @@ static long watchdog_next_keepalive(struct watchdog_device *wdd)
* after the most recent ping from userspace, the last
* worker ping has to come in hw_heartbeat_ms before this timeout.
*/
- last_heartbeat = virt_timeout - msecs_to_jiffies(hw_heartbeat_ms);
- return min_t(long, last_heartbeat - jiffies, keepalive_interval);
+ last_heartbeat = ktime_sub(virt_timeout, ms_to_ktime(hw_heartbeat_ms));
+ latest_heartbeat = ktime_sub(last_heartbeat, ktime_get());
+ if (ktime_before(latest_heartbeat, keepalive_interval))
+ return latest_heartbeat;
+ return keepalive_interval;
}

static inline void watchdog_update_worker(struct watchdog_device *wdd)
@@ -137,29 +138,33 @@ static inline void watchdog_update_worker(struct watchdog_device *wdd)
struct watchdog_core_data *wd_data = wdd->wd_data;

if (watchdog_need_worker(wdd)) {
- long t = watchdog_next_keepalive(wdd);
+ ktime_t t = watchdog_next_keepalive(wdd);

if (t > 0)
- mod_delayed_work(watchdog_wq, &wd_data->work, t);
+ hrtimer_start(&wd_data->timer, t, HRTIMER_MODE_REL);
} else {
- cancel_delayed_work(&wd_data->work);
+ hrtimer_cancel(&wd_data->timer);
}
}

static int __watchdog_ping(struct watchdog_device *wdd)
{
struct watchdog_core_data *wd_data = wdd->wd_data;
- unsigned long earliest_keepalive = wd_data->last_hw_keepalive +
- msecs_to_jiffies(wdd->min_hw_heartbeat_ms);
+ ktime_t earliest_keepalive, now;
int err;

- if (time_is_after_jiffies(earliest_keepalive)) {
- mod_delayed_work(watchdog_wq, &wd_data->work,
- earliest_keepalive - jiffies);
+ earliest_keepalive = ktime_add(wd_data->last_hw_keepalive,
+ ms_to_ktime(wdd->min_hw_heartbeat_ms));
+ now = ktime_get();
+
+ if (ktime_after(earliest_keepalive, now)) {
+ hrtimer_start(&wd_data->timer,
+ ktime_sub(earliest_keepalive, now),
+ HRTIMER_MODE_REL);
return 0;
}

- wd_data->last_hw_keepalive = jiffies;
+ wd_data->last_hw_keepalive = now;

if (wdd->ops->ping)
err = wdd->ops->ping(wdd); /* ping the watchdog */
@@ -192,7 +197,7 @@ static int watchdog_ping(struct watchdog_device *wdd)

set_bit(_WDOG_KEEPALIVE, &wd_data->status);

- wd_data->last_keepalive = jiffies;
+ wd_data->last_keepalive = ktime_get();
return __watchdog_ping(wdd);
}

@@ -203,17 +208,18 @@ 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)
+enum hrtimer_restart watchdog_ping_work(struct hrtimer *timer)
{
struct watchdog_core_data *wd_data;

- wd_data = container_of(to_delayed_work(work), struct watchdog_core_data,
- work);
+ wd_data = container_of(timer, struct watchdog_core_data, timer);

mutex_lock(&wd_data->lock);
if (watchdog_worker_should_ping(wd_data))
__watchdog_ping(wd_data->wdd);
mutex_unlock(&wd_data->lock);
+
+ return HRTIMER_NORESTART;
}

/*
@@ -230,7 +236,7 @@ static void watchdog_ping_work(struct work_struct *work)
static int watchdog_start(struct watchdog_device *wdd)
{
struct watchdog_core_data *wd_data = wdd->wd_data;
- unsigned long started_at;
+ ktime_t started_at;
int err;

if (watchdog_active(wdd))
@@ -238,7 +244,7 @@ static int watchdog_start(struct watchdog_device *wdd)

set_bit(_WDOG_KEEPALIVE, &wd_data->status);

- started_at = jiffies;
+ started_at = ktime_get();
if (watchdog_hw_running(wdd) && wdd->ops->ping)
err = wdd->ops->ping(wdd);
else
@@ -919,10 +925,8 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
wd_data->wdd = wdd;
wdd->wd_data = wd_data;

- if (!watchdog_wq)
- return -ENODEV;
-
- INIT_DELAYED_WORK(&wd_data->work, watchdog_ping_work);
+ hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ wd_data->timer.function = watchdog_ping_work;

if (wdd->id == 0) {
old_wd_data = wd_data;
@@ -958,7 +962,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
}

/* Record time of most recent heartbeat as 'just before now'. */
- wd_data->last_hw_keepalive = jiffies - 1;
+ wd_data->last_hw_keepalive = ktime_get();

/*
* If the watchdog is running, prevent its driver from being unloaded,
@@ -968,7 +972,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
if (handle_boot_enabled) {
__module_get(wdd->ops->owner);
kref_get(&wd_data->kref);
- queue_delayed_work(watchdog_wq, &wd_data->work, 0);
+ hrtimer_start(&wd_data->timer, 0, HRTIMER_MODE_REL);
} else {
pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n",
wdd->id);
@@ -1006,7 +1010,7 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
watchdog_stop(wdd);
}

- cancel_delayed_work_sync(&wd_data->work);
+ hrtimer_cancel(&wd_data->timer);

kref_put(&wd_data->kref, watchdog_core_data_release);
}
@@ -1111,13 +1115,6 @@ int __init watchdog_dev_init(void)
{
int err;

- watchdog_wq = alloc_workqueue("watchdogd",
- WQ_HIGHPRI | WQ_MEM_RECLAIM, 0);
- if (!watchdog_wq) {
- pr_err("Failed to create watchdog workqueue\n");
- return -ENOMEM;
- }
-
err = class_register(&watchdog_class);
if (err < 0) {
pr_err("couldn't register class\n");
@@ -1135,7 +1132,6 @@ int __init watchdog_dev_init(void)
err_alloc:
class_unregister(&watchdog_class);
err_register:
- destroy_workqueue(watchdog_wq);
return err;
}

@@ -1149,7 +1145,6 @@ void __exit watchdog_dev_exit(void)
{
unregister_chrdev_region(watchdog_devt, MAX_DOGS);
class_unregister(&watchdog_class);
- destroy_workqueue(watchdog_wq);
}

module_param(handle_boot_enabled, bool, 0444);
--
2.13.3
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