Message-ID: <ed9e0944-fc75-6705-98ea-3f6cf86f5053@sony.com>
Date:   Sat, 24 Apr 2021 15:27:32 +0000
From:   <Peter.Enderborg@...y.com>
To:     <linux@...ck-us.net>, <wim@...ux-watchdog.org>,
        <akpm@...ux-foundation.org>, <linux-watchdog@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <shakeelb@...gle.com>
Subject: Re: [RFC PATCH] watchdog: Adding softwatchdog

On 4/24/21 4:41 PM, Guenter Roeck wrote:
> 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

Do you have better idea where the re-invented wheel might
fit better if it not for watchdog API?


>
>>  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@...y.com
>> + */
>> +
>> +#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;
>>

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