Commit a0a1a5fd authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: reimplement workqueue freeze using max_active 



Currently, workqueue freezing is implemented by marking the worker
freezeable and calling try_to_freeze() from dispatch loop.
Reimplement it using cwq->limit so that the workqueue is frozen
instead of the worker.

* workqueue_struct->saved_max_active is added which stores the
  specified max_active on initialization.

* On freeze, all cwq->max_active's are quenched to zero.  Freezing is
  complete when nr_active on all cwqs reach zero.

* On thaw, all cwq->max_active's are restored to wq->saved_max_active
  and the worklist is repopulated.

This new implementation allows having single shared pool of workers
per cpu.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 1e19ffc6

include/linux/workqueue.h

+7 −0
Original line number Diff line number Diff line
@@ -340,4 +340,11 @@ static inline long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg) 
#else

long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg);

#endif /* CONFIG_SMP */



#ifdef CONFIG_FREEZER

extern void freeze_workqueues_begin(void);

extern bool freeze_workqueues_busy(void);

extern void thaw_workqueues(void);

#endif /* CONFIG_FREEZER */



#endif

kernel/power/process.c

+19 −2
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/syscalls.h>

#include <linux/freezer.h>

#include <linux/delay.h>

#include <linux/workqueue.h>



/* 

 * Timeout for stopping processes
@@ -35,6 +36,7 @@ static int try_to_freeze_tasks(bool sig_only) 
	struct task_struct *g, *p;

	unsigned long end_time;

	unsigned int todo;

	bool wq_busy = false;

	struct timeval start, end;

	u64 elapsed_csecs64;

	unsigned int elapsed_csecs;
@@ -42,6 +44,10 @@ static int try_to_freeze_tasks(bool sig_only) 
	do_gettimeofday(&start);



	end_time = jiffies + TIMEOUT;



	if (!sig_only)

		freeze_workqueues_begin();



	while (true) {

		todo = 0;

		read_lock(&tasklist_lock);
@@ -63,6 +69,12 @@ static int try_to_freeze_tasks(bool sig_only) 
				todo++;

		} while_each_thread(g, p);

		read_unlock(&tasklist_lock);



		if (!sig_only) {

			wq_busy = freeze_workqueues_busy();

			todo += wq_busy;

		}



		if (!todo || time_after(jiffies, end_time))

			break;
@@ -86,8 +98,12 @@ static int try_to_freeze_tasks(bool sig_only) 
		 */

		printk("\n");

		printk(KERN_ERR "Freezing of tasks failed after %d.%02d seconds "

				"(%d tasks refusing to freeze):\n",

				elapsed_csecs / 100, elapsed_csecs % 100, todo);

		       "(%d tasks refusing to freeze, wq_busy=%d):\n",

		       elapsed_csecs / 100, elapsed_csecs % 100,

		       todo - wq_busy, wq_busy);



		thaw_workqueues();



		read_lock(&tasklist_lock);

		do_each_thread(g, p) {

			task_lock(p);
@@ -157,6 +173,7 @@ void thaw_processes(void) 
	oom_killer_enable();



	printk("Restarting tasks ... ");

	thaw_workqueues();

	thaw_tasks(true);

	thaw_tasks(false);

	schedule();

kernel/workqueue.c

+153 −10
Original line number Diff line number Diff line
@@ -78,7 +78,7 @@ struct cpu_workqueue_struct { 
	int			nr_in_flight[WORK_NR_COLORS];

						/* L: nr of in_flight works */

	int			nr_active;	/* L: nr of active works */

	int			max_active;	/* I: max active works */

	int			max_active;	/* L: max active works */

	struct list_head	delayed_works;	/* L: delayed works */

};
@@ -108,6 +108,7 @@ struct workqueue_struct { 
	struct list_head	flusher_queue;	/* F: flush waiters */

	struct list_head	flusher_overflow; /* F: flush overflow list */



	int			saved_max_active; /* I: saved cwq max_active */

	const char		*name;		/* I: workqueue name */

#ifdef CONFIG_LOCKDEP

	struct lockdep_map	lockdep_map;
@@ -228,6 +229,7 @@ static inline void debug_work_deactivate(struct work_struct *work) { } 
static DEFINE_SPINLOCK(workqueue_lock);

static LIST_HEAD(workqueues);

static DEFINE_PER_CPU(struct ida, worker_ida);

static bool workqueue_freezing;		/* W: have wqs started freezing? */



static int worker_thread(void *__worker);
@@ -745,19 +747,13 @@ static int worker_thread(void *__worker) 
	struct cpu_workqueue_struct *cwq = worker->cwq;

	DEFINE_WAIT(wait);



	if (cwq->wq->flags & WQ_FREEZEABLE)

		set_freezable();



	for (;;) {

		prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);

		if (!freezing(current) &&

		    !kthread_should_stop() &&

		if (!kthread_should_stop() &&

		    list_empty(&cwq->worklist))

			schedule();

		finish_wait(&cwq->more_work, &wait);



		try_to_freeze();



		if (kthread_should_stop())

			break;
@@ -1553,6 +1549,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name, 
		goto err;



	wq->flags = flags;

	wq->saved_max_active = max_active;

	mutex_init(&wq->flush_mutex);

	atomic_set(&wq->nr_cwqs_to_flush, 0);

	INIT_LIST_HEAD(&wq->flusher_queue);
@@ -1591,8 +1588,19 @@ struct workqueue_struct *__create_workqueue_key(const char *name, 
			failed = true;

	}



	/*

	 * workqueue_lock protects global freeze state and workqueues

	 * list.  Grab it, set max_active accordingly and add the new

	 * workqueue to workqueues list.

	 */

	spin_lock(&workqueue_lock);



	if (workqueue_freezing && wq->flags & WQ_FREEZEABLE)

		for_each_possible_cpu(cpu)

			get_cwq(cpu, wq)->max_active = 0;



	list_add(&wq->list, &workqueues);



	spin_unlock(&workqueue_lock);



	cpu_maps_update_done();
@@ -1621,14 +1629,18 @@ void destroy_workqueue(struct workqueue_struct *wq) 
{

	int cpu;



	flush_workqueue(wq);



	/*

	 * wq list is used to freeze wq, remove from list after

	 * flushing is complete in case freeze races us.

	 */

	cpu_maps_update_begin();

	spin_lock(&workqueue_lock);

	list_del(&wq->list);

	spin_unlock(&workqueue_lock);

	cpu_maps_update_done();



	flush_workqueue(wq);



	for_each_possible_cpu(cpu) {

		struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);

		int i;
@@ -1722,6 +1734,137 @@ long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg) 
EXPORT_SYMBOL_GPL(work_on_cpu);

#endif /* CONFIG_SMP */



#ifdef CONFIG_FREEZER



/**

 * freeze_workqueues_begin - begin freezing workqueues

 *

 * Start freezing workqueues.  After this function returns, all

 * freezeable workqueues will queue new works to their frozen_works

 * list instead of the cwq ones.

 *

 * CONTEXT:

 * Grabs and releases workqueue_lock and cwq->lock's.

 */

void freeze_workqueues_begin(void)

{

	struct workqueue_struct *wq;

	unsigned int cpu;



	spin_lock(&workqueue_lock);



	BUG_ON(workqueue_freezing);

	workqueue_freezing = true;



	for_each_possible_cpu(cpu) {

		list_for_each_entry(wq, &workqueues, list) {

			struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);



			spin_lock_irq(&cwq->lock);



			if (wq->flags & WQ_FREEZEABLE)

				cwq->max_active = 0;



			spin_unlock_irq(&cwq->lock);

		}

	}



	spin_unlock(&workqueue_lock);

}



/**

 * freeze_workqueues_busy - are freezeable workqueues still busy?

 *

 * Check whether freezing is complete.  This function must be called

 * between freeze_workqueues_begin() and thaw_workqueues().

 *

 * CONTEXT:

 * Grabs and releases workqueue_lock.

 *

 * RETURNS:

 * %true if some freezeable workqueues are still busy.  %false if

 * freezing is complete.

 */

bool freeze_workqueues_busy(void)

{

	struct workqueue_struct *wq;

	unsigned int cpu;

	bool busy = false;



	spin_lock(&workqueue_lock);



	BUG_ON(!workqueue_freezing);



	for_each_possible_cpu(cpu) {

		/*

		 * nr_active is monotonically decreasing.  It's safe

		 * to peek without lock.

		 */

		list_for_each_entry(wq, &workqueues, list) {

			struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);



			if (!(wq->flags & WQ_FREEZEABLE))

				continue;



			BUG_ON(cwq->nr_active < 0);

			if (cwq->nr_active) {

				busy = true;

				goto out_unlock;

			}

		}

	}

out_unlock:

	spin_unlock(&workqueue_lock);

	return busy;

}



/**

 * thaw_workqueues - thaw workqueues

 *

 * Thaw workqueues.  Normal queueing is restored and all collected

 * frozen works are transferred to their respective cwq worklists.

 *

 * CONTEXT:

 * Grabs and releases workqueue_lock and cwq->lock's.

 */

void thaw_workqueues(void)

{

	struct workqueue_struct *wq;

	unsigned int cpu;



	spin_lock(&workqueue_lock);



	if (!workqueue_freezing)

		goto out_unlock;



	for_each_possible_cpu(cpu) {

		list_for_each_entry(wq, &workqueues, list) {

			struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);



			if (!(wq->flags & WQ_FREEZEABLE))

				continue;



			spin_lock_irq(&cwq->lock);



			/* restore max_active and repopulate worklist */

			cwq->max_active = wq->saved_max_active;



			while (!list_empty(&cwq->delayed_works) &&

			       cwq->nr_active < cwq->max_active)

				cwq_activate_first_delayed(cwq);



			wake_up(&cwq->more_work);



			spin_unlock_irq(&cwq->lock);

		}

	}



	workqueue_freezing = false;

out_unlock:

	spin_unlock(&workqueue_lock);

}

#endif /* CONFIG_FREEZER */



void __init init_workqueues(void)

{

	unsigned int cpu;

CRA Git | Maintained and supported by SUSTech CRA and CCSE