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[PATCH v5 00/20] kthread: Use kthread worker API more widely

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  [PATCH v5 00/20] kthread: Use kthread worker API more widely Petr Mladek <pmladek@suse.com> - 2016-02-22 16:10 +0100
    [PATCH v5 19/20] thermal/intel_powerclamp: Remove duplicated code that starts the kthread Petr Mladek <pmladek@suse.com> - 2016-02-22 16:10 +0100
    [PATCH v5 20/20] thermal/intel_powerclamp: Convert the kthread to kthread worker API Petr Mladek <pmladek@suse.com> - 2016-02-22 16:10 +0100
    [PATCH v5 18/20] memstick/r592: convert r592_io kthread into kthread worker API Petr Mladek <pmladek@suse.com> - 2016-02-22 16:10 +0100
    [PATCH v5 03/20] kthread: Add create_kthread_worker*() Petr Mladek <pmladek@suse.com> - 2016-02-22 16:10 +0100
      Re: [PATCH v5 03/20] kthread: Add create_kthread_worker*() Petr Mladek <pmladek@suse.com> - 2016-02-24 17:00 +0100

#1339610 — [PATCH v5 00/20] kthread: Use kthread worker API more widely

My intention is to make it easier to manipulate and maintain kthreads.
Especially, I want to replace all the custom main cycles with a
generic one. Also I want to make the kthreads sleep in a consistent
state in a common place when there is no work.

My first attempt was with a brand new API (iterant kthread), see
http://thread.gmane.org/gmane.linux.kernel.api/11892 . But I was
directed to improve the existing kthread worker API. This is
the 4th iteration of the new direction.


1nd..10th patches: improve the existing kthread worker API

11th..16th, 18th, 20th patches: convert several kthreads into
      the kthread worker API, namely: khugepaged, ring buffer
      benchmark, hung_task, kmemleak, ipmi, IB/fmr_pool,
      memstick/r592, intel_powerclamp
      
17th, 19th patches: do some preparation steps; they usually do
      some clean up that makes sense even without the conversion.


Changes against v4:

  + added worker->delayed_work_list; it simplified the check
    for pending work; we do not longer need the new timer_active()
    function; also we do not need the link work->timer. On the
    other hand we need to distinguish between the normal and
    the delayed work by a boolean parameter passed to
    the common functions, e.g. __cancel_kthread_work_sync()
    
  + replaced most try_lock repeat cycles with a WARN_ON();
    the API does not allow to use the work with more workers;
    so such a situation would be a bug; it removed the
    complex try_lock_kthread_work() function that supported
    more modes;

  + renamed kthread_work_pending() to queuing_blocked();
    added this function later when really needed

  + renamed try_to_cancel_kthread_work() to __cancel_kthread_work();
    in fact, this a common implementation for the async cancel()
    function

  + removed a dull check for invalid cpu number in
    create_kthread_worker_on_cpu(); removed some other unnecessary
    code structures as suggested by Tejun

  + consistently used bool return value in all new __cancel functions

  + fixed ordering of cpu and flags parameters in
    create_kthread_worker_on_cpu() vs. create_kthread_worker()

  + used memset in the init_kthread_worker()

  + updated many comments as suggested by Tejun and as
    required the above changes

  + removed obsolete patch adding timer_active()

  + removed obsolete patch for using try_lock in flush_kthread_worker()

  + double checked all existing users of kthread worker API
    that they reinitialized the work when the worker was started
    and would not print false warnings; all looked fine

  + added taken acks for the Intel Powerclamp conversion
    

Changes against v3:

  + allow to free struct kthread_work from its callback; do not touch
    the struct from the worker post-mortem; as a side effect, the structure
    must be reinitialized when the worker gets restarted; updated
    khugepaged, and kmemleak accordingly

  + call del_timer_sync() with worker->lock; instead, detect canceling
    in the timer callback and give up an attempt to get the lock there;
    do busy loop with spin_is_locked() to reduce cache bouncing

  + renamed ipmi+func() -> ipmi_kthread_worker_func() as suggested
    by Corey

  + added some collected Reviewed-by

  
Changes against v2:

  + used worker->lock to synchronize the operations with the work
    instead of the PENDING bit as suggested by Tejun Heo; it simplified
    the implementation in several ways

  + added timer_active(); used it together with del_timer_sync()
    to cancel the work a less tricky way

  + removed the controversial conversion of the RCU kthreads

  + added several other examples: hung_task, kmemleak, ipmi,
    IB/fmr_pool, memstick/r592, intel_powerclamp

  + the helper fixes for the ring buffer benchmark has been improved
    as suggested by Steven; they already are in the Linus tree now

  + fixed a possible race between the check for existing khugepaged
    worker and queuing the work
 

Changes against v1:

  + remove wrappers to manipulate the scheduling policy and priority

  + remove questionable wakeup_and_destroy_kthread_worker() variant

  + do not check for chained work when draining the queue

  + allocate struct kthread worker in create_kthread_work() and
    use more simple checks for running worker

  + add support for delayed kthread works and use them instead
    of waiting inside the works

  + rework the "unrelated" fixes for the ring buffer benchmark
    as discussed in the 1st RFC; also sent separately

  + convert also the consumer in the ring buffer benchmark


I have tested this patch set against the stable Linus tree
for 4.5-rc5.

Comments against v3 can be found at
http://thread.gmane.org/gmane.linux.kernel.mm/144964


Petr Mladek (20):
  kthread/smpboot: Do not park in kthread_create_on_cpu()
  kthread: Allow to call __kthread_create_on_node() with va_list args
  kthread: Add create_kthread_worker*()
  kthread: Add drain_kthread_worker()
  kthread: Add destroy_kthread_worker()
  kthread: Detect when a kthread work is used by more workers
  kthread: Initial support for delayed kthread work
  kthread: Allow to cancel kthread work
  kthread: Allow to modify delayed kthread work
  kthread: Better support freezable kthread workers
  mm/huge_page: Convert khugepaged() into kthread worker API
  ring_buffer: Convert benchmark kthreads into kthread worker API
  hung_task: Convert hungtaskd into kthread worker API
  kmemleak: Convert kmemleak kthread into kthread worker API
  ipmi: Convert kipmi kthread into kthread worker API
  IB/fmr_pool: Convert the cleanup thread into kthread worker API
  memstick/r592: Better synchronize debug messages in r592_io kthread
  memstick/r592: convert r592_io kthread into kthread worker API
  thermal/intel_powerclamp: Remove duplicated code that starts the
    kthread
  thermal/intel_powerclamp: Convert the kthread to kthread worker API

 drivers/char/ipmi/ipmi_si_intf.c     | 121 ++++----
 drivers/infiniband/core/fmr_pool.c   |  54 ++--
 drivers/memstick/host/r592.c         |  61 ++--
 drivers/memstick/host/r592.h         |   5 +-
 drivers/thermal/intel_powerclamp.c   | 302 +++++++++++--------
 include/linux/kthread.h              |  56 ++++
 kernel/hung_task.c                   |  41 ++-
 kernel/kthread.c                     | 555 +++++++++++++++++++++++++++++++----
 kernel/smpboot.c                     |   5 +
 kernel/trace/ring_buffer_benchmark.c | 133 ++++-----
 mm/huge_memory.c                     | 138 +++++----
 mm/kmemleak.c                        |  87 +++---
 12 files changed, 1064 insertions(+), 494 deletions(-)

CC: Catalin Marinas <catalin.marinas@arm.com>
CC: linux-watchdog@vger.kernel.org
CC: Corey Minyard <minyard@acm.org>
CC: openipmi-developer@lists.sourceforge.net
CC: Doug Ledford <dledford@redhat.com>
CC: Sean Hefty <sean.hefty@intel.com>
CC: Hal Rosenstock <hal.rosenstock@gmail.com>
CC: linux-rdma@vger.kernel.org
CC: Maxim Levitsky <maximlevitsky@gmail.com>
CC: Zhang Rui <rui.zhang@intel.com>
CC: Eduardo Valentin <edubezval@gmail.com>
CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
CC: linux-pm@vger.kernel.org

-- 
1.8.5.6

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#1339611 — [PATCH v5 19/20] thermal/intel_powerclamp: Remove duplicated code that starts the kthread

This patch removes a code duplication. It does not modify
the functionality.

Signed-off-by: Petr Mladek <pmladek@suse.com>
CC: Zhang Rui <rui.zhang@intel.com>
CC: Eduardo Valentin <edubezval@gmail.com>
CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
CC: linux-pm@vger.kernel.org
Acked-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
---
 drivers/thermal/intel_powerclamp.c | 45 +++++++++++++++++---------------------
 1 file changed, 20 insertions(+), 25 deletions(-)

diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
index 6c79588251d5..cb32c38f9828 100644
--- a/drivers/thermal/intel_powerclamp.c
+++ b/drivers/thermal/intel_powerclamp.c
@@ -505,10 +505,27 @@ static void poll_pkg_cstate(struct work_struct *dummy)
 		schedule_delayed_work(&poll_pkg_cstate_work, HZ);
 }
 
+static void start_power_clamp_thread(unsigned long cpu)
+{
+	struct task_struct **p = per_cpu_ptr(powerclamp_thread, cpu);
+	struct task_struct *thread;
+
+	thread = kthread_create_on_node(clamp_thread,
+					(void *) cpu,
+					cpu_to_node(cpu),
+					"kidle_inject/%ld", cpu);
+	if (IS_ERR(thread))
+		return;
+
+	/* bind to cpu here */
+	kthread_bind(thread, cpu);
+	wake_up_process(thread);
+	*p = thread;
+}
+
 static int start_power_clamp(void)
 {
 	unsigned long cpu;
-	struct task_struct *thread;
 
 	/* check if pkg cstate counter is completely 0, abort in this case */
 	if (!has_pkg_state_counter()) {
@@ -530,20 +547,7 @@ static int start_power_clamp(void)
 
 	/* start one thread per online cpu */
 	for_each_online_cpu(cpu) {
-		struct task_struct **p =
-			per_cpu_ptr(powerclamp_thread, cpu);
-
-		thread = kthread_create_on_node(clamp_thread,
-						(void *) cpu,
-						cpu_to_node(cpu),
-						"kidle_inject/%ld", cpu);
-		/* bind to cpu here */
-		if (likely(!IS_ERR(thread))) {
-			kthread_bind(thread, cpu);
-			wake_up_process(thread);
-			*p = thread;
-		}
-
+		start_power_clamp_thread(cpu);
 	}
 	put_online_cpus();
 
@@ -575,7 +579,6 @@ static int powerclamp_cpu_callback(struct notifier_block *nfb,
 				unsigned long action, void *hcpu)
 {
 	unsigned long cpu = (unsigned long)hcpu;
-	struct task_struct *thread;
 	struct task_struct **percpu_thread =
 		per_cpu_ptr(powerclamp_thread, cpu);
 
@@ -584,15 +587,7 @@ static int powerclamp_cpu_callback(struct notifier_block *nfb,
 
 	switch (action) {
 	case CPU_ONLINE:
-		thread = kthread_create_on_node(clamp_thread,
-						(void *) cpu,
-						cpu_to_node(cpu),
-						"kidle_inject/%lu", cpu);
-		if (likely(!IS_ERR(thread))) {
-			kthread_bind(thread, cpu);
-			wake_up_process(thread);
-			*percpu_thread = thread;
-		}
+		start_power_clamp_thread(cpu);
 		/* prefer BSP as controlling CPU */
 		if (cpu == 0) {
 			control_cpu = 0;
-- 
1.8.5.6

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#1339612 — [PATCH v5 20/20] thermal/intel_powerclamp: Convert the kthread to kthread worker API

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 the intel powerclamp kthreads into the kthread
worker because they need to have a good control over the assigned
CPUs.

IMHO, the most natural way is to split one cycle into two works.
First one does some balancing and let the CPU work normal
way for some time. The second work checks what the CPU has done
in the meantime and put it into C-state to reach the required
idle time ratio. The delay between the two works is achieved
by the delayed kthread work.

The two works have to share some data that used to be local
variables of the single kthread function. This is achieved
by the new per-CPU struct kthread_worker_data. It might look
as a complication. On the other hand, the long original kthread
function was not nice either.

The patch tries to avoid extra init and cleanup works. All the
actions might be done outside the thread. They are moved
to the functions that create or destroy the worker. Especially,
I checked that the timers are assigned to the right CPU.

The two works are queuing each other. It makes it a bit tricky to
break it when we want to stop the worker. We use the global and
per-worker "clamping" variables to make sure that the re-queuing
eventually stops. We also cancel the works to make it faster.
Note that the canceling is not reliable because the handling
of the two variables and queuing is not synchronized via a lock.
But it is not a big deal because it is just an optimization.
The job is stopped faster than before in most cases.

Signed-off-by: Petr Mladek <pmladek@suse.com>
CC: Zhang Rui <rui.zhang@intel.com>
CC: Eduardo Valentin <edubezval@gmail.com>
CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
CC: linux-pm@vger.kernel.org
Acked-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
---
 drivers/thermal/intel_powerclamp.c | 287 ++++++++++++++++++++++---------------
 1 file changed, 168 insertions(+), 119 deletions(-)

diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
index cb32c38f9828..964102c2330c 100644
--- a/drivers/thermal/intel_powerclamp.c
+++ b/drivers/thermal/intel_powerclamp.c
@@ -86,11 +86,27 @@ static unsigned int control_cpu; /* The cpu assigned to collect stat and update
 				  */
 static bool clamping;
 
+static const struct sched_param sparam = {
+	.sched_priority = MAX_USER_RT_PRIO / 2,
+};
+struct powerclamp_worker_data {
+	struct kthread_worker *worker;
+	struct kthread_work balancing_work;
+	struct delayed_kthread_work idle_injection_work;
+	struct timer_list wakeup_timer;
+	unsigned int cpu;
+	unsigned int count;
+	unsigned int guard;
+	unsigned int window_size_now;
+	unsigned int target_ratio;
+	unsigned int duration_jiffies;
+	bool clamping;
+};
 
-static struct task_struct * __percpu *powerclamp_thread;
+static struct powerclamp_worker_data * __percpu worker_data;
 static struct thermal_cooling_device *cooling_dev;
 static unsigned long *cpu_clamping_mask;  /* bit map for tracking per cpu
-					   * clamping thread
+					   * clamping kthread worker
 					   */
 
 static unsigned int duration;
@@ -368,100 +384,102 @@ static bool powerclamp_adjust_controls(unsigned int target_ratio,
 	return set_target_ratio + guard <= current_ratio;
 }
 
-static int clamp_thread(void *arg)
+static void clamp_balancing_func(struct kthread_work *work)
 {
-	int cpunr = (unsigned long)arg;
-	DEFINE_TIMER(wakeup_timer, noop_timer, 0, 0);
-	static const struct sched_param param = {
-		.sched_priority = MAX_USER_RT_PRIO/2,
-	};
-	unsigned int count = 0;
-	unsigned int target_ratio;
+	struct powerclamp_worker_data *w_data;
+	int sleeptime;
+	unsigned long target_jiffies;
+	unsigned int compensation;
+	int interval; /* jiffies to sleep for each attempt */
 
-	set_bit(cpunr, cpu_clamping_mask);
-	set_freezable();
-	init_timer_on_stack(&wakeup_timer);
-	sched_setscheduler(current, SCHED_FIFO, &param);
-
-	while (true == clamping && !kthread_should_stop() &&
-		cpu_online(cpunr)) {
-		int sleeptime;
-		unsigned long target_jiffies;
-		unsigned int guard;
-		unsigned int compensation = 0;
-		int interval; /* jiffies to sleep for each attempt */
-		unsigned int duration_jiffies = msecs_to_jiffies(duration);
-		unsigned int window_size_now;
-
-		try_to_freeze();
-		/*
-		 * make sure user selected ratio does not take effect until
-		 * the next round. adjust target_ratio if user has changed
-		 * target such that we can converge quickly.
-		 */
-		target_ratio = set_target_ratio;
-		guard = 1 + target_ratio/20;
-		window_size_now = window_size;
-		count++;
+	w_data = container_of(work, struct powerclamp_worker_data,
+			      balancing_work);
 
-		/*
-		 * systems may have different ability to enter package level
-		 * c-states, thus we need to compensate the injected idle ratio
-		 * to achieve the actual target reported by the HW.
-		 */
-		compensation = get_compensation(target_ratio);
-		interval = duration_jiffies*100/(target_ratio+compensation);
-
-		/* align idle time */
-		target_jiffies = roundup(jiffies, interval);
-		sleeptime = target_jiffies - jiffies;
-		if (sleeptime <= 0)
-			sleeptime = 1;
-		schedule_timeout_interruptible(sleeptime);
-		/*
-		 * only elected controlling cpu can collect stats and update
-		 * control parameters.
-		 */
-		if (cpunr == control_cpu && !(count%window_size_now)) {
-			should_skip =
-				powerclamp_adjust_controls(target_ratio,
-							guard, window_size_now);
-			smp_mb();
-		}
+	/*
+	 * make sure user selected ratio does not take effect until
+	 * the next round. adjust target_ratio if user has changed
+	 * target such that we can converge quickly.
+	 */
+	w_data->target_ratio = READ_ONCE(set_target_ratio);
+	w_data->guard = 1 + w_data->target_ratio / 20;
+	w_data->window_size_now = window_size;
+	w_data->duration_jiffies = msecs_to_jiffies(duration);
+	w_data->count++;
+
+	/*
+	 * systems may have different ability to enter package level
+	 * c-states, thus we need to compensate the injected idle ratio
+	 * to achieve the actual target reported by the HW.
+	 */
+	compensation = get_compensation(w_data->target_ratio);
+	interval = w_data->duration_jiffies * 100 /
+		(w_data->target_ratio + compensation);
+
+	/* align idle time */
+	target_jiffies = roundup(jiffies, interval);
+	sleeptime = target_jiffies - jiffies;
+	if (sleeptime <= 0)
+		sleeptime = 1;
+
+	if (clamping && w_data->clamping && cpu_online(w_data->cpu))
+		queue_delayed_kthread_work(w_data->worker,
+					   &w_data->idle_injection_work,
+					   sleeptime);
+}
+
+static void clamp_idle_injection_func(struct kthread_work *work)
+{
+	struct powerclamp_worker_data *w_data;
+	unsigned long target_jiffies;
+
+	w_data = container_of(work, struct powerclamp_worker_data,
+			      idle_injection_work.work);
+
+	/*
+	 * only elected controlling cpu can collect stats and update
+	 * control parameters.
+	 */
+	if (w_data->cpu == control_cpu &&
+	    !(w_data->count % w_data->window_size_now)) {
+		should_skip =
+			powerclamp_adjust_controls(w_data->target_ratio,
+						   w_data->guard,
+						   w_data->window_size_now);
+		smp_mb();
+	}
 
-		if (should_skip)
-			continue;
+	if (should_skip)
+		goto balance;
+
+	target_jiffies = jiffies + w_data->duration_jiffies;
+	mod_timer(&w_data->wakeup_timer, target_jiffies);
+	if (unlikely(local_softirq_pending()))
+		goto balance;
+	/*
+	 * stop tick sched during idle time, interrupts are still
+	 * allowed. thus jiffies are updated properly.
+	 */
+	preempt_disable();
+	/* mwait until target jiffies is reached */
+	while (time_before(jiffies, target_jiffies)) {
+		unsigned long ecx = 1;
+		unsigned long eax = target_mwait;
 
-		target_jiffies = jiffies + duration_jiffies;
-		mod_timer(&wakeup_timer, target_jiffies);
-		if (unlikely(local_softirq_pending()))
-			continue;
 		/*
-		 * stop tick sched during idle time, interrupts are still
-		 * allowed. thus jiffies are updated properly.
+		 * REVISIT: may call enter_idle() to notify drivers who
+		 * can save power during cpu idle. same for exit_idle()
 		 */
-		preempt_disable();
-		/* mwait until target jiffies is reached */
-		while (time_before(jiffies, target_jiffies)) {
-			unsigned long ecx = 1;
-			unsigned long eax = target_mwait;
-
-			/*
-			 * REVISIT: may call enter_idle() to notify drivers who
-			 * can save power during cpu idle. same for exit_idle()
-			 */
-			local_touch_nmi();
-			stop_critical_timings();
-			mwait_idle_with_hints(eax, ecx);
-			start_critical_timings();
-			atomic_inc(&idle_wakeup_counter);
-		}
-		preempt_enable();
+		local_touch_nmi();
+		stop_critical_timings();
+		mwait_idle_with_hints(eax, ecx);
+		start_critical_timings();
+		atomic_inc(&idle_wakeup_counter);
 	}
-	del_timer_sync(&wakeup_timer);
-	clear_bit(cpunr, cpu_clamping_mask);
+	preempt_enable();
 
-	return 0;
+balance:
+	if (clamping && w_data->clamping && cpu_online(w_data->cpu))
+		queue_kthread_work(w_data->worker, &w_data->balancing_work);
 }
 
 /*
@@ -505,22 +523,58 @@ static void poll_pkg_cstate(struct work_struct *dummy)
 		schedule_delayed_work(&poll_pkg_cstate_work, HZ);
 }
 
-static void start_power_clamp_thread(unsigned long cpu)
+static void start_power_clamp_worker(unsigned long cpu)
 {
-	struct task_struct **p = per_cpu_ptr(powerclamp_thread, cpu);
-	struct task_struct *thread;
-
-	thread = kthread_create_on_node(clamp_thread,
-					(void *) cpu,
-					cpu_to_node(cpu),
-					"kidle_inject/%ld", cpu);
-	if (IS_ERR(thread))
+	struct powerclamp_worker_data *w_data = per_cpu_ptr(worker_data, cpu);
+	struct kthread_worker *worker;
+
+	worker = create_kthread_worker_on_cpu(cpu, KTW_FREEZABLE,
+					      "kidle_inject/%ld");
+	if (IS_ERR(worker))
 		return;
 
-	/* bind to cpu here */
-	kthread_bind(thread, cpu);
-	wake_up_process(thread);
-	*p = thread;
+	w_data->worker = worker;
+	w_data->count = 0;
+	w_data->cpu = cpu;
+	w_data->clamping = true;
+	set_bit(cpu, cpu_clamping_mask);
+	setup_timer(&w_data->wakeup_timer, noop_timer, 0);
+	sched_setscheduler(worker->task, SCHED_FIFO, &sparam);
+	init_kthread_work(&w_data->balancing_work, clamp_balancing_func);
+	init_delayed_kthread_work(&w_data->idle_injection_work,
+				  clamp_idle_injection_func);
+	queue_kthread_work(w_data->worker, &w_data->balancing_work);
+}
+
+static void stop_power_clamp_worker(unsigned long cpu)
+{
+	struct powerclamp_worker_data *w_data = per_cpu_ptr(worker_data, cpu);
+
+	if (!w_data->worker)
+		return;
+
+	w_data->clamping = false;
+	/*
+	 * Make sure that all works that get queued after this point see
+	 * the clamping disabled. The counter part is not needed because
+	 * there is an implicit memory barrier when the queued work
+	 * is proceed.
+	 */
+	smp_wmb();
+	cancel_kthread_work_sync(&w_data->balancing_work);
+	cancel_delayed_kthread_work_sync(&w_data->idle_injection_work);
+	/*
+	 * The balancing work still might be queued here because
+	 * the handling of the "clapming" variable, cancel, and queue
+	 * operations are not synchronized via a lock. But it is not
+	 * a big deal. The balancing work is fast and destroy kthread
+	 * will wait for it.
+	 */
+	del_timer_sync(&w_data->wakeup_timer);
+	clear_bit(w_data->cpu, cpu_clamping_mask);
+	destroy_kthread_worker(w_data->worker);
+
+	w_data->worker = NULL;
 }
 
 static int start_power_clamp(void)
@@ -545,9 +599,9 @@ static int start_power_clamp(void)
 	clamping = true;
 	schedule_delayed_work(&poll_pkg_cstate_work, 0);
 
-	/* start one thread per online cpu */
+	/* start one kthread worker per online cpu */
 	for_each_online_cpu(cpu) {
-		start_power_clamp_thread(cpu);
+		start_power_clamp_worker(cpu);
 	}
 	put_online_cpus();
 
@@ -557,20 +611,17 @@ static int start_power_clamp(void)
 static void end_power_clamp(void)
 {
 	int i;
-	struct task_struct *thread;
 
-	clamping = false;
 	/*
-	 * make clamping visible to other cpus and give per cpu clamping threads
-	 * sometime to exit, or gets killed later.
+	 * Block requeuing in all the kthread workers. They will drain and
+	 * stop faster.
 	 */
-	smp_mb();
-	msleep(20);
+	clamping = false;
 	if (bitmap_weight(cpu_clamping_mask, num_possible_cpus())) {
 		for_each_set_bit(i, cpu_clamping_mask, num_possible_cpus()) {
-			pr_debug("clamping thread for cpu %d alive, kill\n", i);
-			thread = *per_cpu_ptr(powerclamp_thread, i);
-			kthread_stop(thread);
+			pr_debug("clamping worker for cpu %d alive, destroy\n",
+				 i);
+			stop_power_clamp_worker(i);
 		}
 	}
 }
@@ -579,15 +630,13 @@ static int powerclamp_cpu_callback(struct notifier_block *nfb,
 				unsigned long action, void *hcpu)
 {
 	unsigned long cpu = (unsigned long)hcpu;
-	struct task_struct **percpu_thread =
-		per_cpu_ptr(powerclamp_thread, cpu);
 
 	if (false == clamping)
 		goto exit_ok;
 
 	switch (action) {
 	case CPU_ONLINE:
-		start_power_clamp_thread(cpu);
+		start_power_clamp_worker(cpu);
 		/* prefer BSP as controlling CPU */
 		if (cpu == 0) {
 			control_cpu = 0;
@@ -598,7 +647,7 @@ static int powerclamp_cpu_callback(struct notifier_block *nfb,
 		if (test_bit(cpu, cpu_clamping_mask)) {
 			pr_err("cpu %lu dead but powerclamping thread is not\n",
 				cpu);
-			kthread_stop(*percpu_thread);
+			stop_power_clamp_worker(cpu);
 		}
 		if (cpu == control_cpu) {
 			control_cpu = smp_processor_id();
@@ -785,8 +834,8 @@ static int __init powerclamp_init(void)
 	window_size = 2;
 	register_hotcpu_notifier(&powerclamp_cpu_notifier);
 
-	powerclamp_thread = alloc_percpu(struct task_struct *);
-	if (!powerclamp_thread) {
+	worker_data = alloc_percpu(struct powerclamp_worker_data);
+	if (!worker_data) {
 		retval = -ENOMEM;
 		goto exit_unregister;
 	}
@@ -806,7 +855,7 @@ static int __init powerclamp_init(void)
 	return 0;
 
 exit_free_thread:
-	free_percpu(powerclamp_thread);
+	free_percpu(worker_data);
 exit_unregister:
 	unregister_hotcpu_notifier(&powerclamp_cpu_notifier);
 exit_free:
@@ -819,7 +868,7 @@ static void __exit powerclamp_exit(void)
 {
 	unregister_hotcpu_notifier(&powerclamp_cpu_notifier);
 	end_power_clamp();
-	free_percpu(powerclamp_thread);
+	free_percpu(worker_data);
 	thermal_cooling_device_unregister(cooling_dev);
 	kfree(cpu_clamping_mask);
 
-- 
1.8.5.6

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#1339618 — [PATCH v5 18/20] memstick/r592: convert r592_io kthread into kthread worker API

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 the r592_io kthread into the kthread worker
API. I am not sure how busy the kthread is and if anyone would
like to control the resources. It is well possible that a workqueue
would be perfectly fine. Well, the conversion between kthread
worker API and workqueues is pretty trivial.

The patch moves one iteration from the kthread into the kthread
worker function. It helps to remove all the hackery with process
state and kthread_should_stop().

The work is queued instead of waking the thread.

The work is explicitly canceled before the worker is destroyed.
It is self-queuing and it might take a long time until the queue
is drained, otherwise.

Important: The change is only compile tested. I did not find an easy
way how to check it in use.

Signed-off-by: Petr Mladek <pmladek@suse.com>
CC: Maxim Levitsky <maximlevitsky@gmail.com>
---
 drivers/memstick/host/r592.c | 58 ++++++++++++++++++++------------------------
 drivers/memstick/host/r592.h |  3 ++-
 2 files changed, 28 insertions(+), 33 deletions(-)

diff --git a/drivers/memstick/host/r592.c b/drivers/memstick/host/r592.c
index dd73c5506fdf..9d7cc27d8edc 100644
--- a/drivers/memstick/host/r592.c
+++ b/drivers/memstick/host/r592.c
@@ -563,40 +563,32 @@ out:
 	return;
 }
 
-/* Main request processing thread */
-static int r592_process_thread(void *data)
+/* Main request processing work */
+static void r592_process_func(struct kthread_work *work)
 {
 	int error;
-	struct r592_device *dev = (struct r592_device *)data;
-
-	while (!kthread_should_stop()) {
-		if (!dev->io_started) {
-			dbg_verbose("IO: started");
-			dev->io_started = true;
-		}
-
-		set_current_state(TASK_INTERRUPTIBLE);
-		error = memstick_next_req(dev->host, &dev->req);
+	struct r592_device *dev =
+		container_of(work, struct r592_device, io_work);
 
-		if (error) {
-			if (error == -ENXIO || error == -EAGAIN) {
-				dbg_verbose("IO: done");
-			} else {
-				dbg("IO: unknown error from "
-					"memstick_next_req %d", error);
-			}
-			dev->io_started = false;
+	if (!dev->io_started) {
+		dbg_verbose("IO: started");
+		dev->io_started = true;
+	}
 
-			if (kthread_should_stop())
-				set_current_state(TASK_RUNNING);
+	error = memstick_next_req(dev->host, &dev->req);
 
-			schedule();
+	if (error) {
+		if (error == -ENXIO || error == -EAGAIN) {
+			dbg_verbose("IO: done");
 		} else {
-			set_current_state(TASK_RUNNING);
-			r592_execute_tpc(dev);
+			dbg("IO: unknown error from memstick_next_req %d",
+			    error);
 		}
+		dev->io_started = false;
+	} else {
+		r592_execute_tpc(dev);
+		queue_kthread_work(dev->io_worker, &dev->io_work);
 	}
-	return 0;
 }
 
 /* Reprogram chip to detect change in card state */
@@ -721,7 +713,7 @@ static void r592_submit_req(struct memstick_host *host)
 	if (dev->req)
 		return;
 
-	wake_up_process(dev->io_thread);
+	queue_kthread_work(dev->io_worker, &dev->io_work);
 }
 
 static const struct pci_device_id r592_pci_id_tbl[] = {
@@ -779,9 +771,10 @@ static int r592_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	r592_check_dma(dev);
 
 	dev->io_started = false;
-	dev->io_thread = kthread_run(r592_process_thread, dev, "r592_io");
-	if (IS_ERR(dev->io_thread)) {
-		error = PTR_ERR(dev->io_thread);
+	init_kthread_work(&dev->io_work, r592_process_func);
+	dev->io_worker = create_kthread_worker(0, "r592_io");
+	if (IS_ERR(dev->io_worker)) {
+		error = PTR_ERR(dev->io_worker);
 		goto error5;
 	}
 
@@ -807,7 +800,7 @@ error6:
 		dma_free_coherent(&pdev->dev, PAGE_SIZE, dev->dummy_dma_page,
 			dev->dummy_dma_page_physical_address);
 
-	kthread_stop(dev->io_thread);
+	destroy_kthread_worker(dev->io_worker);
 error5:
 	iounmap(dev->mmio);
 error4:
@@ -827,7 +820,8 @@ static void r592_remove(struct pci_dev *pdev)
 
 	/* Stop the processing thread.
 	That ensures that we won't take any more requests */
-	kthread_stop(dev->io_thread);
+	cancel_kthread_work_sync(&dev->io_work);
+	destroy_kthread_worker(dev->io_worker);
 
 	r592_enable_device(dev, false);
 
diff --git a/drivers/memstick/host/r592.h b/drivers/memstick/host/r592.h
index aa8f0f22f4ce..1ac71380ac04 100644
--- a/drivers/memstick/host/r592.h
+++ b/drivers/memstick/host/r592.h
@@ -139,7 +139,8 @@ struct r592_device {
 	spinlock_t irq_lock;
 	struct timer_list detect_timer;
 
-	struct task_struct *io_thread;
+	struct kthread_worker *io_worker;
+	struct kthread_work io_work;
 	bool io_started;
 	bool parallel_mode;
 
-- 
1.8.5.6

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#1339619 — [PATCH v5 03/20] kthread: Add create_kthread_worker*()

Kthread workers are currently created using the classic kthread API,
namely kthread_run(). kthread_worker_fn() is passed as the @threadfn
parameter.

This patch defines create_kthread_worker() and
create_kthread_worker_on_cpu() functions that hide implementation details.

They enforce using kthread_worker_fn() for the main thread. But I doubt
that there are any plans to create any alternative. In fact, I think
that we do not want any alternative main thread because it would be
hard to support consistency with the rest of the kthread worker API.

The naming and function is inspired by the workqueues API like the rest
of the kthread worker API.

Note that we need to bind per-CPU kthread workers already when they are
created. It makes the life easier. kthread_bind() could not be used later
for an already running worker.

This patch does _not_ convert existing kthread workers. The kthread worker
API need more improvements first, e.g. a function to destroy the worker.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h |  7 ++++
 kernel/kthread.c        | 95 +++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 92 insertions(+), 10 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index e691b6a23f72..943900c7ce35 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -124,6 +124,13 @@ extern void __init_kthread_worker(struct kthread_worker *worker,
 
 int kthread_worker_fn(void *worker_ptr);
 
+__printf(1, 2)
+struct kthread_worker *
+create_kthread_worker(const char namefmt[], ...);
+
+struct kthread_worker *
+create_kthread_worker_on_cpu(int cpu, const char namefmt[]);
+
 bool queue_kthread_work(struct kthread_worker *worker,
 			struct kthread_work *work);
 void flush_kthread_work(struct kthread_work *work);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index bfe8742c4217..aedaebfd33f4 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -567,23 +567,24 @@ EXPORT_SYMBOL_GPL(__init_kthread_worker);
  * kthread_worker_fn - kthread function to process kthread_worker
  * @worker_ptr: pointer to initialized kthread_worker
  *
- * This function can be used as @threadfn to kthread_create() or
- * kthread_run() with @worker_ptr argument pointing to an initialized
- * kthread_worker.  The started kthread will process work_list until
- * the it is stopped with kthread_stop().  A kthread can also call
- * this function directly after extra initialization.
+ * This function implements the main cycle of kthread worker. It processes
+ * work_list until it is stopped with kthread_stop(). It sleeps when the queue
+ * is empty.
  *
- * Different kthreads can be used for the same kthread_worker as long
- * as there's only one kthread attached to it at any given time.  A
- * kthread_worker without an attached kthread simply collects queued
- * kthread_works.
+ * The works are not allowed to keep any locks, disable preemption or interrupts
+ * when they finish. There is defined a safe point for freezing when one work
+ * finishes and before a new one is started.
  */
 int kthread_worker_fn(void *worker_ptr)
 {
 	struct kthread_worker *worker = worker_ptr;
 	struct kthread_work *work;
 
-	WARN_ON(worker->task);
+	/*
+	 * FIXME: Update the check and remove the assignment when all kthread
+	 * worker users are created using create_kthread_worker*() functions.
+	 */
+	WARN_ON(worker->task && worker->task != current);
 	worker->task = current;
 repeat:
 	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
@@ -617,6 +618,80 @@ repeat:
 }
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
+static struct kthread_worker *
+__create_kthread_worker(int cpu, const char namefmt[], va_list args)
+{
+	struct kthread_worker *worker;
+	struct task_struct *task;
+
+	worker = kzalloc(sizeof(*worker), GFP_KERNEL);
+	if (!worker)
+		return ERR_PTR(-ENOMEM);
+
+	init_kthread_worker(worker);
+
+	if (cpu >= 0)
+		task = kthread_create_on_cpu(kthread_worker_fn, worker,
+					     cpu, namefmt);
+	else
+		task = __kthread_create_on_node(kthread_worker_fn, worker,
+						-1, namefmt, args);
+	if (IS_ERR(task))
+		goto fail_task;
+
+	worker->task = task;
+	wake_up_process(task);
+	return worker;
+
+fail_task:
+	kfree(worker);
+	return ERR_CAST(task);
+}
+
+/**
+ * create_kthread_worker - create a kthread worker
+ * @namefmt: printf-style name for the kthread worker (task).
+ *
+ * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
+ * when the worker was SIGKILLed.
+ */
+struct kthread_worker *
+create_kthread_worker(const char namefmt[], ...)
+{
+	struct kthread_worker *worker;
+	va_list args;
+
+	va_start(args, namefmt);
+	worker = __create_kthread_worker(-1, namefmt, args);
+	va_end(args);
+
+	return worker;
+}
+EXPORT_SYMBOL(create_kthread_worker);
+
+/**
+ * create_kthread_worker_on_cpu - create a kthread worker and bind it
+ *	it to a given CPU and the associated NUMA node.
+ * @cpu: CPU number
+ * @namefmt: printf-style name for the kthread worker (task).
+ *
+ * Use a valid CPU number if you want to bind the kthread worker
+ * to the given CPU and the associated NUMA node.
+ *
+ * @namefmt might include one "%d" that will get replaced by CPU number.
+ *
+ * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
+ * when the worker was SIGKILLed.
+ */
+struct kthread_worker *
+create_kthread_worker_on_cpu(int cpu, const char namefmt[])
+{
+	return __create_kthread_worker(cpu, namefmt, NULL);
+}
+EXPORT_SYMBOL(create_kthread_worker_on_cpu);
+
 /* insert @work before @pos in @worker */
 static void insert_kthread_work(struct kthread_worker *worker,
 			       struct kthread_work *work,
-- 
1.8.5.6

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#1342147 — Re: [PATCH v5 03/20] kthread: Add create_kthread_worker*()

On Mon 2016-02-22 23:48:53, kbuild test robot wrote:
> Hi Petr,
> 
> [auto build test ERROR on soc-thermal/next]
> [also build test ERROR on v4.5-rc5 next-20160222]
> [if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Petr-Mladek/kthread-Use-kthread-worker-API-more-widely/20160222-230250
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/evalenti/linux-soc-thermal next
> config: xtensa-allyesconfig (attached as .config)
> reproduce:
>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=xtensa 
> 
> All error/warnings (new ones prefixed by >>):
> 
>    kernel/kthread.c: In function 'create_kthread_worker_on_cpu':
> >> kernel/kthread.c:691:9: error: incompatible type for argument 3 of '__create_kthread_worker'
>      return __create_kthread_worker(cpu, namefmt, NULL);
>             ^
>    kernel/kthread.c:622:1: note: expected 'va_list' but argument is of type 'void *'
>     __create_kthread_worker(int cpu, const char namefmt[], va_list args)
>     ^
> >> kernel/kthread.c:692:1: warning: control reaches end of non-void function [-Wreturn-type]
>     }
>     ^
> 
> vim +/__create_kthread_worker +691 kernel/kthread.c
> 
>    685	 * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
>    686	 * when the worker was SIGKILLed.
>    687	 */
>    688	struct kthread_worker *
>    689	create_kthread_worker_on_cpu(int cpu, const char namefmt[])
>    690	{
>  > 691		return __create_kthread_worker(cpu, namefmt, NULL);
>  > 692	}
>    693	EXPORT_SYMBOL(create_kthread_worker_on_cpu);
>    694	
>    695	/* insert @work before @pos in @worker */

I can be fixed by passing a fake va_list. It is not used when
__create_kthread_worker() is called with a valid CPU number.

See below an updated patch that passes the build.


From 5e6c252921c0370a88d2ce5f61370fef573afcaa Mon Sep 17 00:00:00 2001
From: Petr Mladek <pmladek@suse.com>
Date: Tue, 23 Jun 2015 17:09:19 +0200
Subject: [PATCH 3/3] kthread: Add create_kthread_worker*()

Kthread workers are currently created using the classic kthread API,
namely kthread_run(). kthread_worker_fn() is passed as the @threadfn
parameter.

This patch defines create_kthread_worker() and
create_kthread_worker_on_cpu() functions that hide implementation details.

They enforce using kthread_worker_fn() for the main thread. But I doubt
that there are any plans to create any alternative. In fact, I think
that we do not want any alternative main thread because it would be
hard to support consistency with the rest of the kthread worker API.

The naming and function is inspired by the workqueues API like the rest
of the kthread worker API.

Note that we need to bind per-CPU kthread workers already when they are
created. It makes the life easier. kthread_bind() could not be used later
for an already running worker.

This patch does _not_ convert existing kthread workers. The kthread worker
API need more improvements first, e.g. a function to destroy the worker.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h |  7 ++++
 kernel/kthread.c        | 97 ++++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 94 insertions(+), 10 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index e691b6a23f72..943900c7ce35 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -124,6 +124,13 @@ extern void __init_kthread_worker(struct kthread_worker *worker,
 
 int kthread_worker_fn(void *worker_ptr);
 
+__printf(1, 2)
+struct kthread_worker *
+create_kthread_worker(const char namefmt[], ...);
+
+struct kthread_worker *
+create_kthread_worker_on_cpu(int cpu, const char namefmt[]);
+
 bool queue_kthread_work(struct kthread_worker *worker,
 			struct kthread_work *work);
 void flush_kthread_work(struct kthread_work *work);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index bfe8742c4217..cd46276f2690 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -567,23 +567,24 @@ EXPORT_SYMBOL_GPL(__init_kthread_worker);
  * kthread_worker_fn - kthread function to process kthread_worker
  * @worker_ptr: pointer to initialized kthread_worker
  *
- * This function can be used as @threadfn to kthread_create() or
- * kthread_run() with @worker_ptr argument pointing to an initialized
- * kthread_worker.  The started kthread will process work_list until
- * the it is stopped with kthread_stop().  A kthread can also call
- * this function directly after extra initialization.
+ * This function implements the main cycle of kthread worker. It processes
+ * work_list until it is stopped with kthread_stop(). It sleeps when the queue
+ * is empty.
  *
- * Different kthreads can be used for the same kthread_worker as long
- * as there's only one kthread attached to it at any given time.  A
- * kthread_worker without an attached kthread simply collects queued
- * kthread_works.
+ * The works are not allowed to keep any locks, disable preemption or interrupts
+ * when they finish. There is defined a safe point for freezing when one work
+ * finishes and before a new one is started.
  */
 int kthread_worker_fn(void *worker_ptr)
 {
 	struct kthread_worker *worker = worker_ptr;
 	struct kthread_work *work;
 
-	WARN_ON(worker->task);
+	/*
+	 * FIXME: Update the check and remove the assignment when all kthread
+	 * worker users are created using create_kthread_worker*() functions.
+	 */
+	WARN_ON(worker->task && worker->task != current);
 	worker->task = current;
 repeat:
 	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
@@ -617,6 +618,82 @@ repeat:
 }
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
+static struct kthread_worker *
+__create_kthread_worker(int cpu, const char namefmt[], va_list args)
+{
+	struct kthread_worker *worker;
+	struct task_struct *task;
+
+	worker = kzalloc(sizeof(*worker), GFP_KERNEL);
+	if (!worker)
+		return ERR_PTR(-ENOMEM);
+
+	init_kthread_worker(worker);
+
+	if (cpu >= 0)
+		task = kthread_create_on_cpu(kthread_worker_fn, worker,
+					     cpu, namefmt);
+	else
+		task = __kthread_create_on_node(kthread_worker_fn, worker,
+						-1, namefmt, args);
+	if (IS_ERR(task))
+		goto fail_task;
+
+	worker->task = task;
+	wake_up_process(task);
+	return worker;
+
+fail_task:
+	kfree(worker);
+	return ERR_CAST(task);
+}
+
+/**
+ * create_kthread_worker - create a kthread worker
+ * @namefmt: printf-style name for the kthread worker (task).
+ *
+ * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
+ * when the worker was SIGKILLed.
+ */
+struct kthread_worker *
+create_kthread_worker(const char namefmt[], ...)
+{
+	struct kthread_worker *worker;
+	va_list args;
+
+	va_start(args, namefmt);
+	worker = __create_kthread_worker(-1, namefmt, args);
+	va_end(args);
+
+	return worker;
+}
+EXPORT_SYMBOL(create_kthread_worker);
+
+/**
+ * create_kthread_worker_on_cpu - create a kthread worker and bind it
+ *	it to a given CPU and the associated NUMA node.
+ * @cpu: CPU number
+ * @namefmt: printf-style name for the kthread worker (task).
+ *
+ * Use a valid CPU number if you want to bind the kthread worker
+ * to the given CPU and the associated NUMA node.
+ *
+ * @namefmt might include one "%d" that will get replaced by CPU number.
+ *
+ * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
+ * when the worker was SIGKILLed.
+ */
+struct kthread_worker *
+create_kthread_worker_on_cpu(int cpu, const char namefmt[])
+{
+	va_list fake_args;
+
+	return __create_kthread_worker(cpu, namefmt, fake_args);
+}
+EXPORT_SYMBOL(create_kthread_worker_on_cpu);
+
 /* insert @work before @pos in @worker */
 static void insert_kthread_work(struct kthread_worker *worker,
 			       struct kthread_work *work,
-- 
1.8.5.6

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