Re: [RFC PATCH] watchdog: Adding softwatchdog

[Guenter Roeck]

On 4/24/21 3:25 AM, Peter Enderborg wrote:
> This is not a rebooting watchdog. It's function is to take other
> actions than a hard reboot. On many complex system there is some
> kind of manager that monitor and take action on slow systems.
> Android has it's lowmemorykiller (lmkd), desktops has earlyoom.
> This watchdog can be used to help monitor to preform some basic
> action to keep the monitor running.
> 
> It can also be used standalone. This add a policy that is
> killing the process with highest oom_score_adj and using
> oom functions to it quickly. I think it is a good usecase
> for the patch. Memory siuations can be problematic for
> software that monitor system, but other prolicys can
> should also be possible. Like picking tasks from a memcg, or
> specific UID's or what ever is low priority.
> ---

NACK. Besides this not following the new watchdog API, the task
of a watchdog is to reset the system on failure. Its task is most
definitely not to re-implement the oom killer in any way, shape,
or form.

Guenter


>  drivers/watchdog/Makefile       |   2 +
>  drivers/watchdog/softwatchdog.c | 231 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/watchdog.h   |   6 +
>  mm/oom_kill.c                   |   4 +-
>  4 files changed, 241 insertions(+), 2 deletions(-)
>  create mode 100644 drivers/watchdog/softwatchdog.c
> 
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index f3a6540e725e..bff8f61fe504 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -221,3 +221,5 @@ obj-$(CONFIG_MENZ069_WATCHDOG) += menz69_wdt.o
>  obj-$(CONFIG_RAVE_SP_WATCHDOG) += rave-sp-wdt.o
>  obj-$(CONFIG_STPMIC1_WATCHDOG) += stpmic1_wdt.o
>  obj-$(CONFIG_SL28CPLD_WATCHDOG) += sl28cpld_wdt.o
> +
> +obj-y += softwatchdog.o
> diff --git a/drivers/watchdog/softwatchdog.c b/drivers/watchdog/softwatchdog.c
> new file mode 100644
> index 000000000000..dd7153092da8
> --- /dev/null
> +++ b/drivers/watchdog/softwatchdog.c
> @@ -0,0 +1,231 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Soft watchdog
> + *  This is a RFC of a watchdog does do not reboot the system.
> + *  Instead it do a pre defined action
> + *
> + *  Author: peter.enderborg@xxxxxxxx
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/mm.h>
> +#include <linux/slab.h>
> +#include <linux/oom.h>
> +#include <linux/module.h>
> +#include <linux/moduleparam.h>
> +#include <linux/types.h>
> +#include <linux/timer.h>
> +#include <linux/miscdevice.h>
> +#include <linux/watchdog.h>
> +#include <linux/notifier.h>
> +#include <linux/init.h>
> +#include <linux/fs.h>
> +
> +void wake_oom_reaper(struct task_struct *tsk); /* need to public ... */
> +void __oom_kill_process(struct task_struct *victim, const char *message); /* hmm */
> +
> +static struct timer_list swd_timer;
> +static int heartbeat = 500;
> +static unsigned long swd_is_open;
> +static char expect_close;
> +static bool nowayout = WATCHDOG_NOWAYOUT;
> +
> +/* a example policy doing a process kill by calling
> + *  functions within oom-killer.
> + */
> +static int policy_fast_kill_oom_score_adj(void)
> +{
> +	struct task_struct *tsk;
> +	struct task_struct *selected = NULL;
> +	int highest = 0;
> +
> +	rcu_read_lock();
> +	for_each_process(tsk) {
> +		struct task_struct *candidate;
> +
> +		if (tsk->flags & PF_KTHREAD)
> +			continue;
> +
> +		/* Ignore task if coredump in progress */
> +		if (tsk->mm && tsk->mm->core_state)
> +			continue;
> +		candidate = find_lock_task_mm(tsk);
> +		if (!candidate)
> +			continue;
> +
> +		if (highest < candidate->signal->oom_score_adj) {
> +			/* for test dont kill level 0 */
> +			highest = candidate->signal->oom_score_adj;
> +			selected = candidate;
> +			pr_info("new selected %d %d", selected->pid,
> +				selected->signal->oom_score_adj);
> +		}
> +		task_unlock(candidate);
> +	}
> +	if (selected)
> +		get_task_struct(selected);
> +
> +	rcu_read_unlock();
> +	if (selected) {
> +		int pid = selected->pid;
> +
> +		pr_info("swd killing: %d", selected->pid);
> +		__oom_kill_process(selected, "swd");
> +		return pid;
> +	}
> +	return 0;
> +}
> +
> +static void swd_ping(void)
> +{
> +	mod_timer(&swd_timer, jiffies + heartbeat);
> +}
> +
> +static long swd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> +	void __user *argp = (void __user *)arg;
> +	int __user *p = argp;
> +	int new_heartbeat;
> +	int status;
> +
> +	struct watchdog_info ident = {
> +		.options =		WDIOF_SETTIMEOUT|
> +					WDIOF_MAGICCLOSE|
> +					WDIOF_OOMKILL |
> +					WDIOF_AUTOKILL,
> +		.identity =		"swd",
> +	};
> +
> +	switch (cmd) {
> +	case WDIOC_GETSUPPORT:
> +		return copy_to_user(argp, &ident, sizeof(ident)) ? -EFAULT : 0;
> +	case WDIOC_GETSTATUS:
> +		status = 0;
> +		return put_user(status, p);
> +	case WDIOC_GETBOOTSTATUS:
> +		return put_user(0, p);
> +	case WDIOC_KEEPALIVE:
> +		swd_ping();
> +		return 0;
> +	case WDIOC_SETTIMEOUT:
> +		if (get_user(new_heartbeat, p))
> +			return -EFAULT;
> +		heartbeat = new_heartbeat;
> +		fallthrough;
> +	case WDIOC_GETTIMEOUT:
> +		return put_user(heartbeat, p);
> +	default:
> +		return -ENOTTY;
> +	}
> +	return -ENOTTY;
> +}
> +
> +static void swd_timer_func(struct timer_list *unused)
> +{
> +	int res;
> +
> +	pr_info("swd timer %d\n", heartbeat);
> +	res = policy_fast_kill_oom_score_adj();
> +	if (res)
> +		pr_info("killed %d\n", res);
> +
> +	mod_timer(&swd_timer, jiffies + heartbeat);
> +}
> +
> +static int swd_start(void)
> +{
> +	add_timer(&swd_timer);
> +	return 0;
> +}
> +
> +static int swd_stop(void)
> +{
> +	del_timer(&swd_timer);
> +	return 0;
> +}
> +
> +static int swd_open(struct inode *inode, struct file *file)
> +{
> +	if (test_and_set_bit(0, &swd_is_open))
> +		return -EBUSY;
> +	swd_start();
> +	return stream_open(inode, file);
> +}
> +
> +static int swd_release(struct inode *inode, struct file *file)
> +{
> +	if (expect_close != 42) {
> +		swd_stop();
> +		clear_bit(0, &swd_is_open);
> +	} else {
> +		pr_crit("SWD device closed unexpectedly.  SWD will not stop!\n");
> +		swd_ping();
> +	}
> +	expect_close = 0;
> +	return 0;
> +}
> +static ssize_t swd_write(struct file *file, const char __user *buf,
> +						size_t count, loff_t *ppos)
> +{
> +	if (count) {
> +		if (!nowayout) {
> +			size_t i;
> +
> +			expect_close = 0;
> +			for (i = 0; i != count; i++) {
> +				char c;
> +
> +				if (get_user(c, buf + i))
> +					return -EFAULT;
> +				if (c == 'V')
> +					expect_close = 42;
> +			}
> +		}
> +		swd_ping();
> +	}
> +	return count;
> +}
> +
> +static const struct file_operations swd_fops = {
> +	.owner		= THIS_MODULE,
> +	.llseek		= no_llseek,
> +	 .write		= swd_write,
> +	.unlocked_ioctl	= swd_ioctl,
> +	.compat_ioctl	= compat_ptr_ioctl,
> +	.open		= swd_open,
> +	.release	= swd_release,
> +};
> +
> +static struct miscdevice swd_miscdev = {
> +	.minor	=	WATCHDOG_MINOR,
> +	.name	=	"soft-watchdog",
> +	.fops	=	&swd_fops,
> +};
> +
> +int __init swd_register(void)
> +{
> +	int ret;
> +
> +	pr_info("swd installed with timer");
> +	ret = misc_register(&swd_miscdev);
> +	timer_setup(&swd_timer, swd_timer_func, 0);
> +	return 0;
> +}
> +
> +static int __init swd_init(void)
> +{
> +	return 0;
> +}
> +
> +static void __exit swd_unload(void)
> +{
> +	return;
> +}
> +
> +subsys_initcall(swd_register);
> +
> +module_init(swd_init);
> +module_exit(swd_unload);
> +
> +MODULE_AUTHOR("Peter Enderborg");
> +MODULE_DESCRIPTION("Memory software watchdog");
> +MODULE_LICENSE("GPL");
> diff --git a/include/uapi/linux/watchdog.h b/include/uapi/linux/watchdog.h
> index b15cde5c9054..780987482e2d 100644
> --- a/include/uapi/linux/watchdog.h
> +++ b/include/uapi/linux/watchdog.h
> @@ -48,6 +48,12 @@ struct watchdog_info {
>  #define	WDIOF_PRETIMEOUT	0x0200  /* Pretimeout (in seconds), get/set */
>  #define	WDIOF_ALARMONLY		0x0400	/* Watchdog triggers a management or
>  					   other external alarm not a reboot */
> +#define WDIOF_OOMKILL		0x0800	/* Watchdog trigger process kill as
> +					 *  oom kill
> +					 */
> +#define WDIOF_AUTOKILL		0x1000	/* Watchdog listen to oom notifiy
> +					 * and kills with its policy
> +					 */
>  #define	WDIOF_KEEPALIVEPING	0x8000	/* Keep alive ping reply */
>  
>  #define	WDIOS_DISABLECARD	0x0001	/* Turn off the watchdog timer */
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index fa1cf18bac97..a5f7299af9a3 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -658,7 +658,7 @@ static int oom_reaper(void *unused)
>  	return 0;
>  }
>  
> -static void wake_oom_reaper(struct task_struct *tsk)
> +void wake_oom_reaper(struct task_struct *tsk)
>  {
>  	/* mm is already queued? */
>  	if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
> @@ -856,7 +856,7 @@ static bool task_will_free_mem(struct task_struct *task)
>  	return ret;
>  }
>  
> -static void __oom_kill_process(struct task_struct *victim, const char *message)
> +void __oom_kill_process(struct task_struct *victim, const char *message)
>  {
>  	struct task_struct *p;
>  	struct mm_struct *mm;
>