Re: [PATCH V4 17/20] watchdog/dev: Add tracepoints

[Guenter Roeck <linux@roeck-us.net>]

On 6/16/22 01:44, Daniel Bristot de Oliveira wrote:
> Add a set of tracepoints, enabling the observability of the watchdog
> device interactions with user-space.
> 
> The events are:
> 	watchdog:watchdog_open
> 	watchdog:watchdog_close
> 	watchdog:watchdog_start
> 	watchdog:watchdog_stop
> 	watchdog:watchdog_set_timeout
> 	watchdog:watchdog_ping
> 	watchdog:watchdog_nowayout
> 	watchdog:watchdog_set_keep_alive
> 	watchdog:watchdog_keep_alive
> 	watchdog:watchdog_set_pretimeout
> 	watchdog:watchdog_pretimeout
> 
> Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marco Elver <elver@google.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Shuah Khan <skhan@linuxfoundation.org>
> Cc: Gabriele Paoloni <gpaoloni@redhat.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Clark Williams <williams@redhat.com>
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-trace-devel@vger.kernel.org
> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
> ---
>   drivers/watchdog/watchdog_dev.c        |  43 ++++++++++-
>   drivers/watchdog/watchdog_pretimeout.c |   2 +
>   include/linux/watchdog.h               |   7 +-
>   include/trace/events/watchdog.h        | 101 +++++++++++++++++++++++++
>   4 files changed, 143 insertions(+), 10 deletions(-)
>   create mode 100644 include/trace/events/watchdog.h
> 
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 54903f3c851e..2f28dc5ab763 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -44,6 +44,9 @@
>   #include <linux/watchdog.h>	/* For watchdog specific items */
>   #include <linux/uaccess.h>	/* For copy_to_user/put_user/... */
>   
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/watchdog.h>
> +
>   #include "watchdog_core.h"
>   #include "watchdog_pretimeout.h"
>   
> @@ -130,9 +133,11 @@ static inline void watchdog_update_worker(struct watchdog_device *wdd)
>   	if (watchdog_need_worker(wdd)) {
>   		ktime_t t = watchdog_next_keepalive(wdd);
>   
> -		if (t > 0)
> +		if (t > 0) {
>   			hrtimer_start(&wd_data->timer, t,
>   				      HRTIMER_MODE_REL_HARD);
> +			trace_watchdog_set_keep_alive(wdd, ktime_to_ms(t));
> +		}
>   	} else {
>   		hrtimer_cancel(&wd_data->timer);
>   	}
> @@ -141,7 +146,7 @@ static inline void watchdog_update_worker(struct watchdog_device *wdd)
>   static int __watchdog_ping(struct watchdog_device *wdd)
>   {
>   	struct watchdog_core_data *wd_data = wdd->wd_data;
> -	ktime_t earliest_keepalive, now;
> +	ktime_t earliest_keepalive, now, next_keepalive;
>   	int err;
>   
>   	earliest_keepalive = ktime_add(wd_data->last_hw_keepalive,
> @@ -149,14 +154,16 @@ static int __watchdog_ping(struct watchdog_device *wdd)
>   	now = ktime_get();
>   
>   	if (ktime_after(earliest_keepalive, now)) {
> -		hrtimer_start(&wd_data->timer,
> -			      ktime_sub(earliest_keepalive, now),
> +		next_keepalive = ktime_sub(earliest_keepalive, now);
> +		hrtimer_start(&wd_data->timer, next_keepalive,
>   			      HRTIMER_MODE_REL_HARD);
> +		trace_watchdog_set_keep_alive(wdd, ktime_to_ms(next_keepalive));
>   		return 0;
>   	}
>   
>   	wd_data->last_hw_keepalive = now;
>   
> +	trace_watchdog_ping(wdd);
>   	if (wdd->ops->ping)
>   		err = wdd->ops->ping(wdd);  /* ping the watchdog */
>   	else
> @@ -215,6 +222,7 @@ static void watchdog_ping_work(struct kthread_work *work)
>   	wd_data = container_of(work, struct watchdog_core_data, work);
>   
>   	mutex_lock(&wd_data->lock);
> +	trace_watchdog_keep_alive(wd_data->wdd);
>   	if (watchdog_worker_should_ping(wd_data))
>   		__watchdog_ping(wd_data->wdd);
>   	mutex_unlock(&wd_data->lock);
> @@ -250,6 +258,8 @@ static int watchdog_start(struct watchdog_device *wdd)
>   
>   	set_bit(_WDOG_KEEPALIVE, &wd_data->status);
>   
> +	trace_watchdog_start(wdd);
> +
>   	started_at = ktime_get();
>   	if (watchdog_hw_running(wdd) && wdd->ops->ping) {
>   		err = __watchdog_ping(wdd);
> @@ -294,6 +304,7 @@ static int watchdog_stop(struct watchdog_device *wdd)
>   		return -EBUSY;
>   	}
>   
> +	trace_watchdog_stop(wdd);
>   	if (wdd->ops->stop) {
>   		clear_bit(WDOG_HW_RUNNING, &wdd->status);
>   		err = wdd->ops->stop(wdd);
> @@ -367,6 +378,7 @@ static int watchdog_set_timeout(struct watchdog_device *wdd,
>   	if (watchdog_timeout_invalid(wdd, timeout))
>   		return -EINVAL;
>   
> +	trace_watchdog_set_timeout(wdd, timeout);

The driver has no obligation to set the timeout to the
requested value. It might be more valuable to report both
the requested and the actual values.


>   	if (wdd->ops->set_timeout) {
>   		err = wdd->ops->set_timeout(wdd, timeout);
>   	} else {
> @@ -399,6 +411,8 @@ static int watchdog_set_pretimeout(struct watchdog_device *wdd,
>   	if (watchdog_pretimeout_invalid(wdd, timeout))
>   		return -EINVAL;
>   
> +	trace_watchdog_set_pretimeout(wdd, timeout);
> +

Again, the driver has no obligation to set the timeout to the
requested value.

>   	if (wdd->ops->set_pretimeout && (wdd->info->options & WDIOF_PRETIMEOUT))
>   		err = wdd->ops->set_pretimeout(wdd, timeout);
>   	else
> @@ -430,6 +444,23 @@ static int watchdog_get_timeleft(struct watchdog_device *wdd,
>   	return 0;
>   }
>   
> +/**
> + * watchdog_set_nowayout - set nowaout bit
> + * @wdd:	The watchdog device to set nowayoutbit
> + * @nowayout	A boolean on/off switcher
> + *
> + * If nowayout boolean is true, the nowayout option is set. No action is
> + * taken if nowayout is false.
> + */
> +void watchdog_set_nowayout(struct watchdog_device *wdd, bool nowayout)
> +{
> +	if (nowayout) {
> +		set_bit(WDOG_NO_WAY_OUT, &wdd->status);
> +		trace_watchdog_nowayout(wdd);
> +	}
> +}
> +EXPORT_SYMBOL(watchdog_set_nowayout);
> +
>   #ifdef CONFIG_WATCHDOG_SYSFS
>   static ssize_t nowayout_show(struct device *dev, struct device_attribute *attr,
>   				char *buf)
> @@ -861,6 +892,8 @@ static int watchdog_open(struct inode *inode, struct file *file)
>   		goto out_clear;
>   	}
>   
> +	trace_watchdog_open(wdd);
> +
>   	err = watchdog_start(wdd);
>   	if (err < 0)
>   		goto out_mod;
> @@ -883,6 +916,7 @@ static int watchdog_open(struct inode *inode, struct file *file)
>   	return stream_open(inode, file);
>   
>   out_mod:
> +	trace_watchdog_close(wdd);
>   	module_put(wd_data->wdd->ops->owner);
>   out_clear:
>   	clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
> @@ -944,6 +978,7 @@ static int watchdog_release(struct inode *inode, struct file *file)
>   	/* make sure that /dev/watchdog can be re-opened */
>   	clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
>   
> +	trace_watchdog_close(wdd);
>   done:
>   	running = wdd && watchdog_hw_running(wdd);
>   	mutex_unlock(&wd_data->lock);
> diff --git a/drivers/watchdog/watchdog_pretimeout.c b/drivers/watchdog/watchdog_pretimeout.c
> index 376a495ab80c..58c391ed2205 100644
> --- a/drivers/watchdog/watchdog_pretimeout.c
> +++ b/drivers/watchdog/watchdog_pretimeout.c
> @@ -8,6 +8,7 @@
>   #include <linux/spinlock.h>
>   #include <linux/string.h>
>   #include <linux/watchdog.h>
> +#include <trace/events/watchdog.h>
>   
>   #include "watchdog_core.h"
>   #include "watchdog_pretimeout.h"
> @@ -107,6 +108,7 @@ void watchdog_notify_pretimeout(struct watchdog_device *wdd)
>   		return;
>   	}
>   
> +	trace_watchdog_pretimeout(wdd);
>   	wdd->gov->pretimeout(wdd);
>   	spin_unlock_irqrestore(&pretimeout_lock, flags);
>   }
> diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
> index 99660197a36c..11d93407e492 100644
> --- a/include/linux/watchdog.h
> +++ b/include/linux/watchdog.h
> @@ -139,12 +139,7 @@ static inline bool watchdog_hw_running(struct watchdog_device *wdd)
>   	return test_bit(WDOG_HW_RUNNING, &wdd->status);
>   }
>   
> -/* Use the following function to set the nowayout feature */
> -static inline void watchdog_set_nowayout(struct watchdog_device *wdd, bool nowayout)
> -{
> -	if (nowayout)
> -		set_bit(WDOG_NO_WAY_OUT, &wdd->status);
> -}
> +void watchdog_set_nowayout(struct watchdog_device *wdd, bool nowayout);
>   
>   /* Use the following function to stop the watchdog on reboot */
>   static inline void watchdog_stop_on_reboot(struct watchdog_device *wdd)
> diff --git a/include/trace/events/watchdog.h b/include/trace/events/watchdog.h
> new file mode 100644
> index 000000000000..145cd6cfaa02
> --- /dev/null
> +++ b/include/trace/events/watchdog.h
> @@ -0,0 +1,101 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM watchdog
> +
> +#if !defined(_TRACE_WATCHDOG_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_WATCHDOG_H
> +
> +#include <linux/tracepoint.h>
> +
> +/*
> + * These are all events whose sole argument is the watchdog id.
> + */
> +DECLARE_EVENT_CLASS(dev_operations_template,
> +
> +	TP_PROTO(struct watchdog_device *wdd),
> +
> +	TP_ARGS(wdd),
> +
> +	TP_STRUCT__entry(
> +		__field(__u32, id)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->id = wdd->id;
> +	),
> +
> +	TP_printk("id=%d",
> +		  __entry->id)
> +);
> +
> +DEFINE_EVENT(dev_operations_template, watchdog_open,
> +	     TP_PROTO(struct watchdog_device *wdd),
> +	     TP_ARGS(wdd));
> +
> +DEFINE_EVENT(dev_operations_template, watchdog_close,
> +	     TP_PROTO(struct watchdog_device *wdd),
> +	     TP_ARGS(wdd));
> +
> +DEFINE_EVENT(dev_operations_template, watchdog_start,
> +	     TP_PROTO(struct watchdog_device *wdd),
> +	     TP_ARGS(wdd));
> +
> +DEFINE_EVENT(dev_operations_template, watchdog_stop,
> +	     TP_PROTO(struct watchdog_device *wdd),
> +	     TP_ARGS(wdd));
> +
> +DEFINE_EVENT(dev_operations_template, watchdog_ping,
> +	     TP_PROTO(struct watchdog_device *wdd),
> +	     TP_ARGS(wdd));
> +
> +DEFINE_EVENT(dev_operations_template, watchdog_nowayout,
> +	     TP_PROTO(struct watchdog_device *wdd),
> +	     TP_ARGS(wdd));
> +
> +DEFINE_EVENT(dev_operations_template, watchdog_keep_alive,
> +	     TP_PROTO(struct watchdog_device *wdd),
> +	     TP_ARGS(wdd));
> +
> +DEFINE_EVENT(dev_operations_template, watchdog_pretimeout,
> +	     TP_PROTO(struct watchdog_device *wdd),
> +	     TP_ARGS(wdd));
> +
> +/*
> + * These are all events with a device ID and a given timeout.
> + */
> +DECLARE_EVENT_CLASS(watchdog_timeout_template,
> +
> +	TP_PROTO(struct watchdog_device *wdd, u64 timeout),
> +
> +	TP_ARGS(wdd, timeout),
> +
> +	TP_STRUCT__entry(
> +		__field(__u32, id)
> +		__field(__u64, timeout)


Why u64 ? timeout is unsigned long.

> +	),
> +
> +	TP_fast_assign(
> +		__entry->id		= wdd->id;
> +		__entry->timeout	= timeout;
> +	),
> +
> +	TP_printk("id=%d timeout=%llus",
> +		  __entry->id, __entry->timeout)
> +);
> +
> +DEFINE_EVENT(watchdog_timeout_template, watchdog_set_timeout,
> +	     TP_PROTO(struct watchdog_device *wdd, u64 timeout),
> +	     TP_ARGS(wdd, timeout));
> +
> +DEFINE_EVENT(watchdog_timeout_template, watchdog_set_pretimeout,
> +	     TP_PROTO(struct watchdog_device *wdd, u64 timeout),
> +	     TP_ARGS(wdd, timeout));
> +
> +DEFINE_EVENT(watchdog_timeout_template, watchdog_set_keep_alive,
> +	     TP_PROTO(struct watchdog_device *wdd, u64 timeout),
> +	     TP_ARGS(wdd, timeout));
> +
> +#endif /* _TRACE_WATCHDOG_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>