path: root/kernel/slow-work.c

/* 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/proc_fs.h>
#include "slow-work.h"

static void slow_work_cull_timeout(unsigned long);
static void slow_work_oom_timeout(unsigned long);

#ifdef CONFIG_SYSCTL
static 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_SYSCTL
static 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_MODULES
static 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);
#endif

/*
 * Data for tracking currently executing items for indication through /proc
 */
#ifdef CONFIG_SLOW_WORK_PROC
struct 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