Date:	Mon, 23 Nov 2015 13:36:06 -0600
From:	Corey Minyard <minyard@....org>
To:	Petr Mladek <pmladek@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	Vlastimil Babka <vbabka@...e.cz>, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	openipmi-developer@...ts.sourceforge.net
Subject: Re: [PATCH v3 17/22] ipmi: Convert kipmi kthread into kthread worker
 API



On 11/18/2015 07:25 AM, Petr Mladek wrote:
> Kthreads are currently implemented as an infinite loop. Each
> has its own variant of checks for terminating, freezing,
> awakening. In many cases it is unclear to say in which state
> it is and sometimes it is done a wrong way.
>
> The plan is to convert kthreads into kthread_worker or workqueues
> API. It allows to split the functionality into separate operations.
> It helps to make a better structure. Also it defines a clean state
> where no locks are taken, IRQs blocked, the kthread might sleep
> or even be safely migrated.
>
> The kthread worker API is useful when we want to have a dedicated
> single thread for the work. It helps to make sure that it is
> available when needed. Also it allows a better control, e.g.
> define a scheduling priority.
>
> This patch converts kipmi kthread into the kthread worker API because
> it modifies the scheduling priority. The change is quite straightforward.

I think this is correct.  That code was hard to get right, but I don't
see where any
logic is actually changed.

This also doesn't really look any simpler (you end up with more LOC than
you did before :) ),
though it will make things more consistent and reduce errors and that's
a good thing.

My only comment is I would like the worker function named ipmi_worker,
not ipmi_func.

Reviewed-by: Corey Minyard <cminyard@...sta.com>

> First, we move the per-thread variable "busy_until" into the per-thread
> structure struct smi_info. As a side effect, we could omit one parameter
> in ipmi_thread_busy_wait(). On the other hand, the structure could not
> longer be passed with the const qualifier.
>
> The value of "busy_until" is initialized when the kthread is created.
> Also the scheduling priority is set there. This helps to avoid an extra
> init work.
>
> One iteration of the kthread cycle is moved to a delayed work function.
> The different delays between the cycles are solved the following way:
>
>   + immediate cycle (nope) is converted into goto within the same work
>
>   + immediate cycle with a possible reschedule is converted into
>     re-queuing with a zero delay
>
>   + schedule_timeout() is converted into re-queuing with the given
>     delay
>
>   + interruptible sleep is converted into nothing; The work
>     will get queued again from the check_start_timer_thread().
>     By other words the external wakeup_up_process() will get
>     replaced by queuing with a zero delay.
>
> Probably the most tricky change is when the worker is being stopped.
> We need to explicitly cancel the work to prevent it from re-queuing.
>
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> CC: Corey Minyard <minyard@....org>
> CC: openipmi-developer@...ts.sourceforge.net
> ---
>  drivers/char/ipmi/ipmi_si_intf.c | 116 ++++++++++++++++++++++-----------------
>  1 file changed, 66 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
> index 654f6f36a071..fdb97eaded4b 100644
> --- a/drivers/char/ipmi/ipmi_si_intf.c
> +++ b/drivers/char/ipmi/ipmi_si_intf.c
> @@ -302,7 +302,9 @@ struct smi_info {
>  	/* Counters and things for the proc filesystem. */
>  	atomic_t stats[SI_NUM_STATS];
>  
> -	struct task_struct *thread;
> +	struct kthread_worker *worker;
> +	struct delayed_kthread_work work;
> +	struct timespec64 busy_until;
>  
>  	struct list_head link;
>  	union ipmi_smi_info_union addr_info;
> @@ -929,8 +931,9 @@ static void check_start_timer_thread(struct smi_info *smi_info)
>  	if (smi_info->si_state == SI_NORMAL && smi_info->curr_msg == NULL) {
>  		smi_mod_timer(smi_info, jiffies + SI_TIMEOUT_JIFFIES);
>  
> -		if (smi_info->thread)
> -			wake_up_process(smi_info->thread);
> +		if (smi_info->worker)
> +			mod_delayed_kthread_work(smi_info->worker,
> +						 &smi_info->work, 0);
>  
>  		start_next_msg(smi_info);
>  		smi_event_handler(smi_info, 0);
> @@ -1008,10 +1011,10 @@ static inline int ipmi_si_is_busy(struct timespec64 *ts)
>  }
>  
>  static inline int ipmi_thread_busy_wait(enum si_sm_result smi_result,
> -					const struct smi_info *smi_info,
> -					struct timespec64 *busy_until)
> +					struct smi_info *smi_info)
>  {
>  	unsigned int max_busy_us = 0;
> +	struct timespec64 *busy_until = &smi_info->busy_until;
>  
>  	if (smi_info->intf_num < num_max_busy_us)
>  		max_busy_us = kipmid_max_busy_us[smi_info->intf_num];
> @@ -1042,53 +1045,49 @@ static inline int ipmi_thread_busy_wait(enum si_sm_result smi_result,
>   * (if that is enabled).  See the paragraph on kimid_max_busy_us in
>   * Documentation/IPMI.txt for details.
>   */
> -static int ipmi_thread(void *data)
> +static void ipmi_func(struct kthread_work *work)
>  {
> -	struct smi_info *smi_info = data;
> +	struct smi_info *smi_info = container_of(work, struct smi_info,
> +						 work.work);
>  	unsigned long flags;
>  	enum si_sm_result smi_result;
> -	struct timespec64 busy_until;
> +	int busy_wait;
>  
> -	ipmi_si_set_not_busy(&busy_until);
> -	set_user_nice(current, MAX_NICE);
> -	while (!kthread_should_stop()) {
> -		int busy_wait;
> +next:
> +	spin_lock_irqsave(&(smi_info->si_lock), flags);
> +	smi_result = smi_event_handler(smi_info, 0);
>  
> -		spin_lock_irqsave(&(smi_info->si_lock), flags);
> -		smi_result = smi_event_handler(smi_info, 0);
> +	/*
> +	 * If the driver is doing something, there is a possible
> +	 * race with the timer.  If the timer handler see idle,
> +	 * and the thread here sees something else, the timer
> +	 * handler won't restart the timer even though it is
> +	 * required.  So start it here if necessary.
> +	 */
> +	if (smi_result != SI_SM_IDLE && !smi_info->timer_running)
> +		smi_mod_timer(smi_info, jiffies + SI_TIMEOUT_JIFFIES);
>  
> -		/*
> -		 * If the driver is doing something, there is a possible
> -		 * race with the timer.  If the timer handler see idle,
> -		 * and the thread here sees something else, the timer
> -		 * handler won't restart the timer even though it is
> -		 * required.  So start it here if necessary.
> -		 */
> -		if (smi_result != SI_SM_IDLE && !smi_info->timer_running)
> -			smi_mod_timer(smi_info, jiffies + SI_TIMEOUT_JIFFIES);
> -
> -		spin_unlock_irqrestore(&(smi_info->si_lock), flags);
> -		busy_wait = ipmi_thread_busy_wait(smi_result, smi_info,
> -						  &busy_until);
> -		if (smi_result == SI_SM_CALL_WITHOUT_DELAY)
> -			; /* do nothing */
> -		else if (smi_result == SI_SM_CALL_WITH_DELAY && busy_wait)
> -			schedule();
> -		else if (smi_result == SI_SM_IDLE) {
> -			if (atomic_read(&smi_info->need_watch)) {
> -				schedule_timeout_interruptible(100);
> -			} else {
> -				/* Wait to be woken up when we are needed. */
> -				__set_current_state(TASK_INTERRUPTIBLE);
> -				schedule();
> -			}
> -		} else
> -			schedule_timeout_interruptible(1);
> +	spin_unlock_irqrestore(&(smi_info->si_lock), flags);
> +	busy_wait = ipmi_thread_busy_wait(smi_result, smi_info);
> +
> +	if (smi_result == SI_SM_CALL_WITHOUT_DELAY)
> +		goto next;
> +	if (smi_result == SI_SM_CALL_WITH_DELAY && busy_wait) {
> +		queue_delayed_kthread_work(smi_info->worker,
> +					   &smi_info->work, 0);
> +	} else if (smi_result == SI_SM_IDLE) {
> +		if (atomic_read(&smi_info->need_watch)) {
> +			queue_delayed_kthread_work(smi_info->worker,
> +						   &smi_info->work, 100);
> +		} else {
> +			/* Nope. Wait to be queued when we are needed. */
> +		}
> +	} else {
> +		queue_delayed_kthread_work(smi_info->worker,
> +					   &smi_info->work, 1);
>  	}
> -	return 0;
>  }
>  
> -
>  static void poll(void *send_info)
>  {
>  	struct smi_info *smi_info = send_info;
> @@ -1229,17 +1228,29 @@ static int smi_start_processing(void       *send_info,
>  		enable = 1;
>  
>  	if (enable) {
> -		new_smi->thread = kthread_run(ipmi_thread, new_smi,
> -					      "kipmi%d", new_smi->intf_num);
> -		if (IS_ERR(new_smi->thread)) {
> +		struct kthread_worker *worker;
> +
> +		worker = create_kthread_worker(0, "kipmi%d",
> +					       new_smi->intf_num);
> +
> +		if (IS_ERR(worker)) {
>  			dev_notice(new_smi->dev, "Could not start"
>  				   " kernel thread due to error %ld, only using"
>  				   " timers to drive the interface\n",
> -				   PTR_ERR(new_smi->thread));
> -			new_smi->thread = NULL;
> +				   PTR_ERR(worker));
> +			goto out;
>  		}
> +
> +		ipmi_si_set_not_busy(&new_smi->busy_until);
> +		set_user_nice(worker->task, MAX_NICE);
> +
> +		init_delayed_kthread_work(&new_smi->work, ipmi_func);
> +		queue_delayed_kthread_work(worker, &new_smi->work, 0);
> +
> +		new_smi->worker = worker;
>  	}
>  
> +out:
>  	return 0;
>  }
>  
> @@ -3414,8 +3425,13 @@ static void check_for_broken_irqs(struct smi_info *smi_info)
>  
>  static inline void wait_for_timer_and_thread(struct smi_info *smi_info)
>  {
> -	if (smi_info->thread != NULL)
> -		kthread_stop(smi_info->thread);
> +	if (smi_info->worker != NULL) {
> +		struct kthread_worker *worker = smi_info->worker;
> +
> +		smi_info->worker = NULL;
> +		cancel_delayed_kthread_work_sync(&smi_info->work);
> +		destroy_kthread_worker(worker);
> +	}
>  	if (smi_info->timer_running)
>  		del_timer_sync(&smi_info->si_timer);
>  }

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