/* Worker thread pool for slow items, such as filesystem lookups or mkdirs * * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com) * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public Licence * as published by the Free Software Foundation; either version * 2 of the Licence, or (at your option) any later version. * * See Documentation/slow-work.txt */ #include <linux/module.h>#include <linux/slow-work.h>#include <linux/kthread.h>#include <linux/freezer.h>#include <linux/wait.h>#include <linux/debugfs.h>#include "slow-work.h" static void slow_work_cull_timeout(unsigned long);static void slow_work_oom_timeout(unsigned long); #ifdef CONFIG_SYSCTLstatic int slow_work_min_threads_sysctl(struct ctl_table *, int,					void __user *, size_t *, loff_t *); static int slow_work_max_threads_sysctl(struct ctl_table *, int ,					void __user *, size_t *, loff_t *);#endif /* * The pool of threads has at least min threads in it as long as someone is * using the facility, and may have as many as max. * * A portion of the pool may be processing very slow operations. */static unsigned slow_work_min_threads = 2;static unsigned slow_work_max_threads = 4;static unsigned vslow_work_proportion = 50; /* % of threads that may process					     * very slow work */ #ifdef CONFIG_SYSCTLstatic const int slow_work_min_min_threads = 2;static int slow_work_max_max_threads = SLOW_WORK_THREAD_LIMIT;static const int slow_work_min_vslow = 1;static const int slow_work_max_vslow = 99; ctl_table slow_work_sysctls[] = {	{		.ctl_name	= CTL_UNNUMBERED,		.procname	= "min-threads",		.data		= &slow_work_min_threads,		.maxlen		= sizeof(unsigned),		.mode		= 0644,		.proc_handler	= slow_work_min_threads_sysctl,		.extra1		= (void *) &slow_work_min_min_threads,		.extra2		= &slow_work_max_threads,	},	{		.ctl_name	= CTL_UNNUMBERED,		.procname	= "max-threads",		.data		= &slow_work_max_threads,		.maxlen		= sizeof(unsigned),		.mode		= 0644,		.proc_handler	= slow_work_max_threads_sysctl,		.extra1		= &slow_work_min_threads,		.extra2		= (void *) &slow_work_max_max_threads,	},	{		.ctl_name	= CTL_UNNUMBERED,		.procname	= "vslow-percentage",		.data		= &vslow_work_proportion,		.maxlen		= sizeof(unsigned),		.mode		= 0644,		.proc_handler	= &proc_dointvec_minmax,		.extra1		= (void *) &slow_work_min_vslow,		.extra2		= (void *) &slow_work_max_vslow,	},	{ .ctl_name = 0 }};#endif /* * The active state of the thread pool */static atomic_t slow_work_thread_count;static atomic_t vslow_work_executing_count; static bool slow_work_may_not_start_new_thread;static bool slow_work_cull; /* cull a thread due to lack of activity */static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);static struct slow_work slow_work_new_thread; /* new thread starter */ /* * slow work ID allocation (use slow_work_queue_lock) */static DECLARE_BITMAP(slow_work_ids, SLOW_WORK_THREAD_LIMIT); /* * Unregistration tracking to prevent put_ref() from disappearing during module * unload */#ifdef CONFIG_MODULESstatic struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT];static struct module *slow_work_unreg_module;static struct slow_work *slow_work_unreg_work_item;static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq);static DEFINE_MUTEX(slow_work_unreg_sync_lock); static void slow_work_set_thread_processing(int id, struct slow_work *work){	if (work)		slow_work_thread_processing[id] = work->owner;}static void slow_work_done_thread_processing(int id, struct slow_work *work){	struct module *module = slow_work_thread_processing[id]; 	slow_work_thread_processing[id] = NULL;	smp_mb();	if (slow_work_unreg_work_item == work ||	    slow_work_unreg_module == module)		wake_up_all(&slow_work_unreg_wq);}static void slow_work_clear_thread_processing(int id){	slow_work_thread_processing[id] = NULL;}#elsestatic void slow_work_set_thread_processing(int id, struct slow_work *work) {}static void slow_work_done_thread_processing(int id, struct slow_work *work) {}static void slow_work_clear_thread_processing(int id) {}#endif /* * Data for tracking currently executing items for indication through /proc */#ifdef CONFIG_SLOW_WORK_DEBUGstruct slow_work *slow_work_execs[SLOW_WORK_THREAD_LIMIT];pid_t slow_work_pids[SLOW_WORK_THREAD_LIMIT];DEFINE_RWLOCK(slow_work_execs_lock);#endif /* * The queues of work items and the lock governing access to them.  These are * shared between all the CPUs.  It doesn't make sense to have per-CPU queues * as the number of threads bears no relation to the number of CPUs. * * There are two queues of work items: one for slow work items, and one for * very slow work items. */LIST_HEAD(slow_work_queue);LIST_HEAD(vslow_work_queue);DEFINE_SPINLOCK(slow_work_queue_lock); /* * The following are two wait queues that get pinged when a work item is placed * on an empty queue.  These allow work items that are hogging a thread by * sleeping in a way that could be deferred to yield their thread and enqueue * themselves. */static DECLARE_WAIT_QUEUE_HEAD(slow_work_queue_waits_for_occupation);static DECLARE_WAIT_QUEUE_HEAD(vslow_work_queue_waits_for_occupation); /* * The thread controls.  A variable used to signal to the threads that they * should exit when the queue is empty, a waitqueue used by the threads to wait * for signals, and a completion set by the last thread to exit. */static bool slow_work_threads_should_exit;static DECLARE_WAIT_QUEUE_HEAD(slow_work_thread_wq);static DECLARE_COMPLETION(slow_work_last_thread_exited); /* * The number of users of the thread pool and its lock.  Whilst this is zero we * have no threads hanging around, and when this reaches zero, we wait for all * active or queued work items to complete and kill all the threads we do have. */static int slow_work_user_count;static DEFINE_MUTEX(slow_work_user_lock); static inline int slow_work_get_ref(struct slow_work *work){	if (work->ops->get_ref)		return work->ops->get_ref(work); 	return 0;} static inline void slow_work_put_ref(struct slow_work *work){	if (work->ops->put_ref)		work->ops->put_ref(work);} /* * Calculate the maximum number of active threads in the pool that are * permitted to process very slow work items. * * The answer is rounded up to at least 1, but may not equal or exceed the * maximum number of the threads in the pool.  This means we always have at * least one thread that can process slow work items, and we always have at * least one thread that won't get tied up doing so. */static unsigned slow_work_calc_vsmax(void){	unsigned vsmax; 	vsmax = atomic_read(&slow_work_thread_count) * vslow_work_proportion;	vsmax /= 100;	vsmax = max(vsmax, 1U);	return min(vsmax, slow_work_max_threads - 1);} /* * Attempt to execute stuff queued on a slow thread.  Return true if we managed * it, false if there was nothing to do. */static noinline bool slow_work_execute(int id){	struct slow_work *work = NULL;	unsigned vsmax;	bool very_slow; 	vsmax = slow_work_calc_vsmax(); 	/* see if we can schedule a new thread to be started if we're not	 * keeping up with the work */	if (!waitqueue_active(&slow_work_thread_wq) &&	    (!list_empty(&slow_work_queue) || !list_empty(&vslow_work_queue)) &&	    atomic_read(&slow_work_thread_count) < slow_work_max_threads &&	    !slow_work_may_not_start_new_thread)		slow_work_enqueue(&slow_work_new_thread); 	/* find something to execute */	spin_lock_irq(&slow_work_queue_lock);	if (!list_empty(&vslow_work_queue) &&	    atomic_read(&vslow_work_executing_count) < vsmax) {		work = list_entry(vslow_work_queue.next,				  struct slow_work, link);		if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))			BUG();		list_del_init(&work->link);		atomic_inc(&vslow_work_executing_count);		very_slow = true;	} else if (!list_empty(&slow_work_queue)) {		work = list_entry(slow_work_queue.next,				  struct slow_work, link);		if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))			BUG();		list_del_init(&work->link);		very_slow = false;	} else {		very_slow = false; /* avoid the compiler warning */	} 	slow_work_set_thread_processing(id, work);	if (work) {		slow_work_mark_time(work);		slow_work_begin_exec(id, work);	} 	spin_unlock_irq(&slow_work_queue_lock); 	if (!work)		return false; 	if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))		BUG(); 	/* don't execute if the work is in the process of being cancelled */	if (!test_bit(SLOW_WORK_CANCELLING, &work->flags))		work->ops->execute(work); 	if (very_slow)		atomic_dec(&vslow_work_executing_count);	clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags); 	/* wake up anyone waiting for this work to be complete */	wake_up_bit(&work->flags, SLOW_WORK_EXECUTING); 	slow_work_end_exec(id, work); 	/* if someone tried to enqueue the item whilst we were executing it,	 * then it'll be left unenqueued to avoid multiple threads trying to	 * execute it simultaneously	 *	 * there is, however, a race between us testing the pending flag and	 * getting the spinlock, and between the enqueuer setting the pending	 * flag and getting the spinlock, so we use a deferral bit to tell us	 * if the enqueuer got there first	 */	if (test_bit(SLOW_WORK_PENDING, &work->flags)) {		spin_lock_irq(&slow_work_queue_lock); 		if (!test_bit(SLOW_WORK_EXECUTING, &work->flags) &&		    test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags))			goto auto_requeue; 		spin_unlock_irq(&slow_work_queue_lock);	} 	/* sort out the race between module unloading and put_ref() */	slow_work_put_ref(work);	slow_work_done_thread_processing(id, work); 	return true; auto_requeue:	/* we must complete the enqueue operation	 * - we transfer our ref on the item back to the appropriate queue	 * - don't wake another thread up as we're awake already	 */	slow_work_mark_time(work);	if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))		list_add_tail(&work->link, &vslow_work_queue);	else		list_add_tail(&work->link, &slow_work_queue);	spin_unlock_irq(&slow_work_queue_lock);	slow_work_clear_thread_processing(id);	return true;} /** * slow_work_sleep_till_thread_needed - Sleep till thread needed by other work * work: The work item under execution that wants to sleep * _timeout: Scheduler sleep timeout * * Allow a requeueable work item to sleep on a slow-work processor thread until * that thread is needed to do some other work or the sleep is interrupted by * some other event. * * The caller must set up a wake up event before calling this and must have set * the appropriate sleep mode (such as TASK_UNINTERRUPTIBLE) and tested its own * condition before calling this function as no test is made here. * * False is returned if there is nothing on the queue; true is returned if the * work item should be requeued */bool slow_work_sleep_till_thread_needed(struct slow_work *work,					signed long *_timeout){	wait_queue_head_t *wfo_wq;	struct list_head *queue; 	DEFINE_WAIT(wait); 	if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {		wfo_wq = &vslow_work_queue_waits_for_occupation;		queue = &vslow_work_queue;	} else {		wfo_wq = &slow_work_queue_waits_for_occupation;		queue = &slow_work_queue;	} 	if (!list_empty(queue))		return true; 	add_wait_queue_exclusive(wfo_wq, &wait);	if (list_empty(queue))		*_timeout = schedule_timeout(*_timeout);	finish_wait(wfo_wq, &wait); 	return !list_empty(queue);}EXPORT_SYMBOL(slow_work_sleep_till_thread_needed); /** * slow_work_enqueue - Schedule a slow work item for processing * @work: The work item to queue * * Schedule a slow work item for processing.  If the item is already undergoing * execution, this guarantees not to re-enter the execution routine until the * first execution finishes. * * The item is pinned by this function as it retains a reference to it, managed * through the item operations.  The item is unpinned once it has been * executed. * * An item may hog the thread that is running it for a relatively large amount * of time, sufficient, for example, to perform several lookup, mkdir, create * and setxattr operations.  It may sleep on I/O and may sleep to obtain locks. * * Conversely, if a number of items are awaiting processing, it may take some * time before any given item is given attention.  The number of threads in the * pool may be increased to deal with demand, but only up to a limit. * * If SLOW_WORK_VERY_SLOW is set on the work item, then it will be placed in * the very slow queue, from which only a portion of the threads will be * allowed to pick items to execute.  This ensures that very slow items won't * overly block ones that are just ordinarily slow. * * Returns 0 if successful, -EAGAIN if not (or -ECANCELED if cancelled work is * attempted queued) */int slow_work_enqueue(struct slow_work *work){	wait_queue_head_t *wfo_wq;	struct list_head *queue;	unsigned long flags;	int ret; 	if (test_bit(SLOW_WORK_CANCELLING, &work->flags))		return -ECANCELED; 	BUG_ON(slow_work_user_count <= 0);	BUG_ON(!work);	BUG_ON(!work->ops); 	/* when honouring an enqueue request, we only promise that we will run	 * the work function in the future; we do not promise to run it once	 * per enqueue request	 *	 * we use the PENDING bit to merge together repeat requests without	 * having to disable IRQs and take the spinlock, whilst still	 * maintaining our promise	 */	if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {		if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {			wfo_wq = &vslow_work_queue_waits_for_occupation;			queue = &vslow_work_queue;		} else {			wfo_wq = &slow_work_queue_waits_for_occupation;			queue = &slow_work_queue;		} 		spin_lock_irqsave(&slow_work_queue_lock, flags); 		if (unlikely(test_bit(SLOW_WORK_CANCELLING, &work->flags)))			goto cancelled; 		/* we promise that we will not attempt to execute the work		 * function in more than one thread simultaneously		 *		 * this, however, leaves us with a problem if we're asked to		 * enqueue the work whilst someone is executing the work		 * function as simply queueing the work immediately means that		 * another thread may try executing it whilst it is already		 * under execution		 *		 * to deal with this, we set the ENQ_DEFERRED bit instead of		 * enqueueing, and the thread currently executing the work		 * function will enqueue the work item when the work function		 * returns and it has cleared the EXECUTING bit		 */		if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {			set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);		} else {			ret = slow_work_get_ref(work);			if (ret < 0)				goto failed;			slow_work_mark_time(work);			list_add_tail(&work->link, queue);			wake_up(&slow_work_thread_wq); 			/* if someone who could be requeued is sleeping on a			 * thread, then ask them to yield their thread */			if (work->link.prev == queue)				wake_up(wfo_wq);		} 		spin_unlock_irqrestore(&slow_work_queue_lock, flags);	}	return 0; cancelled:	ret = -ECANCELED;failed:	spin_unlock_irqrestore(&slow_work_queue_lock, flags);	return ret;}EXPORT_SYMBOL(slow_work_enqueue); static int slow_work_wait(void *word){	schedule();	return 0;} /** * slow_work_cancel - Cancel a slow work item * @work: The work item to cancel * * This function will cancel a previously enqueued work item. If we cannot * cancel the work item, it is guarenteed to have run when this function * returns. */void slow_work_cancel(struct slow_work *work){	bool wait = true, put = false; 	set_bit(SLOW_WORK_CANCELLING, &work->flags);	smp_mb(); 	/* if the work item is a delayed work item with an active timer, we	 * need to wait for the timer to finish _before_ getting the spinlock,	 * lest we deadlock against the timer routine

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