/*

   * kernel/workqueue.c - generic async execution with shared worker pool

   *

   * Copyright (C) 2002		Ingo Molnar

   *

   *   Derived from the taskqueue/keventd code by:
   *     David Woodhouse <dwmw2@infradead.org>
   *     Andrew Morton
   *     Kai Petzke <wpp@marie.physik.tu-berlin.de>
   *     Theodore Ts'o <tytso@mit.edu>

   *

   * Made to use alloc_percpu by Christoph Lameter.

   *

   * Copyright (C) 2010		SUSE Linux Products GmbH
   * Copyright (C) 2010		Tejun Heo <tj@kernel.org>

   *

   * This is the generic async execution mechanism.  Work items as are
   * executed in process context.  The worker pool is shared and
   * automatically managed.  There is one worker pool for each CPU and
   * one extra for works which are better served by workers which are
   * not bound to any specific CPU.
   *
   * Please read Documentation/workqueue.txt for details.

   */

  #include <linux/export.h>

  #include <linux/kernel.h>
  #include <linux/sched.h>
  #include <linux/init.h>
  #include <linux/signal.h>
  #include <linux/completion.h>
  #include <linux/workqueue.h>
  #include <linux/slab.h>
  #include <linux/cpu.h>
  #include <linux/notifier.h>
  #include <linux/kthread.h>

  #include <linux/hardirq.h>

  #include <linux/mempolicy.h>

  #include <linux/freezer.h>

  #include <linux/kallsyms.h>
  #include <linux/debug_locks.h>

  #include <linux/lockdep.h>

  #include <linux/idr.h>

  
  #include "workqueue_sched.h"

  enum {

  	/* global_cwq flags */

  	GCWQ_MANAGE_WORKERS	= 1 << 0,	/* need to manage workers */
  	GCWQ_MANAGING_WORKERS	= 1 << 1,	/* managing workers */
  	GCWQ_DISASSOCIATED	= 1 << 2,	/* cpu can't serve workers */

  	GCWQ_FREEZING		= 1 << 3,	/* freeze in progress */

  	GCWQ_HIGHPRI_PENDING	= 1 << 4,	/* highpri works on queue */

  	/* worker flags */
  	WORKER_STARTED		= 1 << 0,	/* started */
  	WORKER_DIE		= 1 << 1,	/* die die die */
  	WORKER_IDLE		= 1 << 2,	/* is idle */

  	WORKER_PREP		= 1 << 3,	/* preparing to run works */

  	WORKER_ROGUE		= 1 << 4,	/* not bound to any cpu */

  	WORKER_REBIND		= 1 << 5,	/* mom is home, come back */

  	WORKER_CPU_INTENSIVE	= 1 << 6,	/* cpu intensive */

  	WORKER_UNBOUND		= 1 << 7,	/* worker is unbound */

  	WORKER_NOT_RUNNING	= WORKER_PREP | WORKER_ROGUE | WORKER_REBIND |

  				  WORKER_CPU_INTENSIVE | WORKER_UNBOUND,

  
  	/* gcwq->trustee_state */
  	TRUSTEE_START		= 0,		/* start */
  	TRUSTEE_IN_CHARGE	= 1,		/* trustee in charge of gcwq */
  	TRUSTEE_BUTCHER		= 2,		/* butcher workers */
  	TRUSTEE_RELEASE		= 3,		/* release workers */
  	TRUSTEE_DONE		= 4,		/* trustee is done */

  
  	BUSY_WORKER_HASH_ORDER	= 6,		/* 64 pointers */
  	BUSY_WORKER_HASH_SIZE	= 1 << BUSY_WORKER_HASH_ORDER,
  	BUSY_WORKER_HASH_MASK	= BUSY_WORKER_HASH_SIZE - 1,

  	MAX_IDLE_WORKERS_RATIO	= 4,		/* 1/4 of busy can be idle */
  	IDLE_WORKER_TIMEOUT	= 300 * HZ,	/* keep idle ones for 5 mins */

  	MAYDAY_INITIAL_TIMEOUT  = HZ / 100 >= 2 ? HZ / 100 : 2,
  						/* call for help after 10ms
  						   (min two ticks) */

  	MAYDAY_INTERVAL		= HZ / 10,	/* and then every 100ms */
  	CREATE_COOLDOWN		= HZ,		/* time to breath after fail */

  	TRUSTEE_COOLDOWN	= HZ / 10,	/* for trustee draining */

  
  	/*
  	 * Rescue workers are used only on emergencies and shared by
  	 * all cpus.  Give -20.
  	 */
  	RESCUER_NICE_LEVEL	= -20,

  };

  
  /*

   * Structure fields follow one of the following exclusion rules.
   *

   * I: Modifiable by initialization/destruction paths and read-only for
   *    everyone else.

   *

   * P: Preemption protected.  Disabling preemption is enough and should
   *    only be modified and accessed from the local cpu.
   *

   * L: gcwq->lock protected.  Access with gcwq->lock held.

   *

   * X: During normal operation, modification requires gcwq->lock and
   *    should be done only from local cpu.  Either disabling preemption
   *    on local cpu or grabbing gcwq->lock is enough for read access.

   *    If GCWQ_DISASSOCIATED is set, it's identical to L.

   *

   * F: wq->flush_mutex protected.
   *

   * W: workqueue_lock protected.

   */

  struct global_cwq;

  /*
   * The poor guys doing the actual heavy lifting.  All on-duty workers
   * are either serving the manager role, on idle list or on busy hash.
   */

  struct worker {

  	/* on idle list while idle, on busy hash table while busy */
  	union {
  		struct list_head	entry;	/* L: while idle */
  		struct hlist_node	hentry;	/* L: while busy */
  	};

  	struct work_struct	*current_work;	/* L: work being processed */

  	struct cpu_workqueue_struct *current_cwq; /* L: current_work's cwq */

  	struct list_head	scheduled;	/* L: scheduled works */

  	struct task_struct	*task;		/* I: worker task */

  	struct global_cwq	*gcwq;		/* I: the associated gcwq */

  	/* 64 bytes boundary on 64bit, 32 on 32bit */
  	unsigned long		last_active;	/* L: last active timestamp */
  	unsigned int		flags;		/* X: flags */

  	int			id;		/* I: worker id */

  	struct work_struct	rebind_work;	/* L: rebind worker to cpu */

  };

  /*

   * Global per-cpu workqueue.  There's one and only one for each cpu
   * and all works are queued and processed here regardless of their
   * target workqueues.

   */
  struct global_cwq {
  	spinlock_t		lock;		/* the gcwq lock */

  	struct list_head	worklist;	/* L: list of pending works */

  	unsigned int		cpu;		/* I: the associated cpu */

  	unsigned int		flags;		/* L: GCWQ_* flags */

  
  	int			nr_workers;	/* L: total number of workers */
  	int			nr_idle;	/* L: currently idle ones */
  
  	/* workers are chained either in the idle_list or busy_hash */

  	struct list_head	idle_list;	/* X: list of idle workers */

  	struct hlist_head	busy_hash[BUSY_WORKER_HASH_SIZE];
  						/* L: hash of busy workers */

  	struct timer_list	idle_timer;	/* L: worker idle timeout */
  	struct timer_list	mayday_timer;	/* L: SOS timer for dworkers */

  	struct ida		worker_ida;	/* L: for worker IDs */

  
  	struct task_struct	*trustee;	/* L: for gcwq shutdown */
  	unsigned int		trustee_state;	/* L: trustee state */
  	wait_queue_head_t	trustee_wait;	/* trustee wait */

  	struct worker		*first_idle;	/* L: first idle worker */

  } ____cacheline_aligned_in_smp;
  
  /*

   * The per-CPU workqueue.  The lower WORK_STRUCT_FLAG_BITS of

   * work_struct->data are used for flags and thus cwqs need to be
   * aligned at two's power of the number of flag bits.

   */
  struct cpu_workqueue_struct {

  	struct global_cwq	*gcwq;		/* I: the associated gcwq */

  	struct workqueue_struct *wq;		/* I: the owning workqueue */

  	int			work_color;	/* L: current color */
  	int			flush_color;	/* L: flushing color */
  	int			nr_in_flight[WORK_NR_COLORS];
  						/* L: nr of in_flight works */

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

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

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

  };

  
  /*

   * Structure used to wait for workqueue flush.
   */
  struct wq_flusher {
  	struct list_head	list;		/* F: list of flushers */
  	int			flush_color;	/* F: flush color waiting for */
  	struct completion	done;		/* flush completion */
  };
  
  /*

   * All cpumasks are assumed to be always set on UP and thus can't be
   * used to determine whether there's something to be done.
   */
  #ifdef CONFIG_SMP
  typedef cpumask_var_t mayday_mask_t;
  #define mayday_test_and_set_cpu(cpu, mask)	\
  	cpumask_test_and_set_cpu((cpu), (mask))
  #define mayday_clear_cpu(cpu, mask)		cpumask_clear_cpu((cpu), (mask))
  #define for_each_mayday_cpu(cpu, mask)		for_each_cpu((cpu), (mask))

  #define alloc_mayday_mask(maskp, gfp)		zalloc_cpumask_var((maskp), (gfp))

  #define free_mayday_mask(mask)			free_cpumask_var((mask))
  #else
  typedef unsigned long mayday_mask_t;
  #define mayday_test_and_set_cpu(cpu, mask)	test_and_set_bit(0, &(mask))
  #define mayday_clear_cpu(cpu, mask)		clear_bit(0, &(mask))
  #define for_each_mayday_cpu(cpu, mask)		if ((cpu) = 0, (mask))
  #define alloc_mayday_mask(maskp, gfp)		true
  #define free_mayday_mask(mask)			do { } while (0)
  #endif

  
  /*
   * The externally visible workqueue abstraction is an array of
   * per-CPU workqueues:
   */
  struct workqueue_struct {

  	unsigned int		flags;		/* W: WQ_* flags */

  	union {
  		struct cpu_workqueue_struct __percpu	*pcpu;
  		struct cpu_workqueue_struct		*single;
  		unsigned long				v;
  	} cpu_wq;				/* I: cwq's */

  	struct list_head	list;		/* W: list of all workqueues */

  
  	struct mutex		flush_mutex;	/* protects wq flushing */
  	int			work_color;	/* F: current work color */
  	int			flush_color;	/* F: current flush color */
  	atomic_t		nr_cwqs_to_flush; /* flush in progress */
  	struct wq_flusher	*first_flusher;	/* F: first flusher */
  	struct list_head	flusher_queue;	/* F: flush waiters */
  	struct list_head	flusher_overflow; /* F: flush overflow list */

  	mayday_mask_t		mayday_mask;	/* cpus requesting rescue */

  	struct worker		*rescuer;	/* I: rescue worker */

  	int			nr_drainers;	/* W: drain in progress */

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

  #ifdef CONFIG_LOCKDEP

  	struct lockdep_map	lockdep_map;

  #endif

  	char			name[];		/* I: workqueue name */

  };

  struct workqueue_struct *system_wq __read_mostly;
  struct workqueue_struct *system_long_wq __read_mostly;
  struct workqueue_struct *system_nrt_wq __read_mostly;

  struct workqueue_struct *system_unbound_wq __read_mostly;

  struct workqueue_struct *system_freezable_wq __read_mostly;

  struct workqueue_struct *system_nrt_freezable_wq __read_mostly;

  EXPORT_SYMBOL_GPL(system_wq);
  EXPORT_SYMBOL_GPL(system_long_wq);
  EXPORT_SYMBOL_GPL(system_nrt_wq);

  EXPORT_SYMBOL_GPL(system_unbound_wq);

  EXPORT_SYMBOL_GPL(system_freezable_wq);

  EXPORT_SYMBOL_GPL(system_nrt_freezable_wq);

  #define CREATE_TRACE_POINTS
  #include <trace/events/workqueue.h>

  #define for_each_busy_worker(worker, i, pos, gcwq)			\
  	for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++)			\
  		hlist_for_each_entry(worker, pos, &gcwq->busy_hash[i], hentry)

  static inline int __next_gcwq_cpu(int cpu, const struct cpumask *mask,
  				  unsigned int sw)
  {
  	if (cpu < nr_cpu_ids) {
  		if (sw & 1) {
  			cpu = cpumask_next(cpu, mask);
  			if (cpu < nr_cpu_ids)
  				return cpu;
  		}
  		if (sw & 2)
  			return WORK_CPU_UNBOUND;
  	}
  	return WORK_CPU_NONE;
  }
  
  static inline int __next_wq_cpu(int cpu, const struct cpumask *mask,
  				struct workqueue_struct *wq)
  {
  	return __next_gcwq_cpu(cpu, mask, !(wq->flags & WQ_UNBOUND) ? 1 : 2);
  }

  /*
   * CPU iterators
   *
   * An extra gcwq is defined for an invalid cpu number
   * (WORK_CPU_UNBOUND) to host workqueues which are not bound to any
   * specific CPU.  The following iterators are similar to
   * for_each_*_cpu() iterators but also considers the unbound gcwq.
   *
   * for_each_gcwq_cpu()		: possible CPUs + WORK_CPU_UNBOUND
   * for_each_online_gcwq_cpu()	: online CPUs + WORK_CPU_UNBOUND
   * for_each_cwq_cpu()		: possible CPUs for bound workqueues,
   *				  WORK_CPU_UNBOUND for unbound workqueues
   */

  #define for_each_gcwq_cpu(cpu)						\
  	for ((cpu) = __next_gcwq_cpu(-1, cpu_possible_mask, 3);		\
  	     (cpu) < WORK_CPU_NONE;					\
  	     (cpu) = __next_gcwq_cpu((cpu), cpu_possible_mask, 3))
  
  #define for_each_online_gcwq_cpu(cpu)					\
  	for ((cpu) = __next_gcwq_cpu(-1, cpu_online_mask, 3);		\
  	     (cpu) < WORK_CPU_NONE;					\
  	     (cpu) = __next_gcwq_cpu((cpu), cpu_online_mask, 3))
  
  #define for_each_cwq_cpu(cpu, wq)					\
  	for ((cpu) = __next_wq_cpu(-1, cpu_possible_mask, (wq));	\
  	     (cpu) < WORK_CPU_NONE;					\
  	     (cpu) = __next_wq_cpu((cpu), cpu_possible_mask, (wq)))

  #ifdef CONFIG_DEBUG_OBJECTS_WORK
  
  static struct debug_obj_descr work_debug_descr;

  static void *work_debug_hint(void *addr)
  {
  	return ((struct work_struct *) addr)->func;
  }

  /*
   * fixup_init is called when:
   * - an active object is initialized
   */
  static int work_fixup_init(void *addr, enum debug_obj_state state)
  {
  	struct work_struct *work = addr;
  
  	switch (state) {
  	case ODEBUG_STATE_ACTIVE:
  		cancel_work_sync(work);
  		debug_object_init(work, &work_debug_descr);
  		return 1;
  	default:
  		return 0;
  	}
  }
  
  /*
   * fixup_activate is called when:
   * - an active object is activated
   * - an unknown object is activated (might be a statically initialized object)
   */
  static int work_fixup_activate(void *addr, enum debug_obj_state state)
  {
  	struct work_struct *work = addr;
  
  	switch (state) {
  
  	case ODEBUG_STATE_NOTAVAILABLE:
  		/*
  		 * This is not really a fixup. The work struct was
  		 * statically initialized. We just make sure that it
  		 * is tracked in the object tracker.
  		 */

  		if (test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work))) {

  			debug_object_init(work, &work_debug_descr);
  			debug_object_activate(work, &work_debug_descr);
  			return 0;
  		}
  		WARN_ON_ONCE(1);
  		return 0;
  
  	case ODEBUG_STATE_ACTIVE:
  		WARN_ON(1);
  
  	default:
  		return 0;
  	}
  }
  
  /*
   * fixup_free is called when:
   * - an active object is freed
   */
  static int work_fixup_free(void *addr, enum debug_obj_state state)
  {
  	struct work_struct *work = addr;
  
  	switch (state) {
  	case ODEBUG_STATE_ACTIVE:
  		cancel_work_sync(work);
  		debug_object_free(work, &work_debug_descr);
  		return 1;
  	default:
  		return 0;
  	}
  }
  
  static struct debug_obj_descr work_debug_descr = {
  	.name		= "work_struct",

  	.debug_hint	= work_debug_hint,

  	.fixup_init	= work_fixup_init,
  	.fixup_activate	= work_fixup_activate,
  	.fixup_free	= work_fixup_free,
  };
  
  static inline void debug_work_activate(struct work_struct *work)
  {
  	debug_object_activate(work, &work_debug_descr);
  }
  
  static inline void debug_work_deactivate(struct work_struct *work)
  {
  	debug_object_deactivate(work, &work_debug_descr);
  }
  
  void __init_work(struct work_struct *work, int onstack)
  {
  	if (onstack)
  		debug_object_init_on_stack(work, &work_debug_descr);
  	else
  		debug_object_init(work, &work_debug_descr);
  }
  EXPORT_SYMBOL_GPL(__init_work);
  
  void destroy_work_on_stack(struct work_struct *work)
  {
  	debug_object_free(work, &work_debug_descr);
  }
  EXPORT_SYMBOL_GPL(destroy_work_on_stack);
  
  #else
  static inline void debug_work_activate(struct work_struct *work) { }
  static inline void debug_work_deactivate(struct work_struct *work) { }
  #endif

  /* Serializes the accesses to the list of workqueues. */
  static DEFINE_SPINLOCK(workqueue_lock);

  static LIST_HEAD(workqueues);

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

  /*
   * The almighty global cpu workqueues.  nr_running is the only field
   * which is expected to be used frequently by other cpus via
   * try_to_wake_up().  Put it in a separate cacheline.
   */

  static DEFINE_PER_CPU(struct global_cwq, global_cwq);

  static DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t, gcwq_nr_running);

  /*
   * Global cpu workqueue and nr_running counter for unbound gcwq.  The
   * gcwq is always online, has GCWQ_DISASSOCIATED set, and all its
   * workers have WORKER_UNBOUND set.
   */
  static struct global_cwq unbound_global_cwq;
  static atomic_t unbound_gcwq_nr_running = ATOMIC_INIT(0);	/* always 0 */

  static int worker_thread(void *__worker);

  static struct global_cwq *get_gcwq(unsigned int cpu)
  {

  	if (cpu != WORK_CPU_UNBOUND)
  		return &per_cpu(global_cwq, cpu);
  	else
  		return &unbound_global_cwq;

  }

  static atomic_t *get_gcwq_nr_running(unsigned int cpu)
  {

  	if (cpu != WORK_CPU_UNBOUND)
  		return &per_cpu(gcwq_nr_running, cpu);
  	else
  		return &unbound_gcwq_nr_running;

  }

  static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
  					    struct workqueue_struct *wq)

  {

  	if (!(wq->flags & WQ_UNBOUND)) {

  		if (likely(cpu < nr_cpu_ids))

  			return per_cpu_ptr(wq->cpu_wq.pcpu, cpu);

  	} else if (likely(cpu == WORK_CPU_UNBOUND))
  		return wq->cpu_wq.single;
  	return NULL;

  }

  static unsigned int work_color_to_flags(int color)
  {
  	return color << WORK_STRUCT_COLOR_SHIFT;
  }
  
  static int get_work_color(struct work_struct *work)
  {
  	return (*work_data_bits(work) >> WORK_STRUCT_COLOR_SHIFT) &
  		((1 << WORK_STRUCT_COLOR_BITS) - 1);
  }
  
  static int work_next_color(int color)
  {
  	return (color + 1) % WORK_NR_COLORS;
  }

  /*

   * A work's data points to the cwq with WORK_STRUCT_CWQ set while the
   * work is on queue.  Once execution starts, WORK_STRUCT_CWQ is
   * cleared and the work data contains the cpu number it was last on.

   *
   * set_work_{cwq|cpu}() and clear_work_data() can be used to set the
   * cwq, cpu or clear work->data.  These functions should only be
   * called while the work is owned - ie. while the PENDING bit is set.
   *
   * get_work_[g]cwq() can be used to obtain the gcwq or cwq
   * corresponding to a work.  gcwq is available once the work has been
   * queued anywhere after initialization.  cwq is available only from
   * queueing until execution starts.

   */

  static inline void set_work_data(struct work_struct *work, unsigned long data,
  				 unsigned long flags)

  {

  	BUG_ON(!work_pending(work));

  	atomic_long_set(&work->data, data | flags | work_static(work));
  }

  static void set_work_cwq(struct work_struct *work,
  			 struct cpu_workqueue_struct *cwq,
  			 unsigned long extra_flags)
  {
  	set_work_data(work, (unsigned long)cwq,

  		      WORK_STRUCT_PENDING | WORK_STRUCT_CWQ | extra_flags);

  }

  static void set_work_cpu(struct work_struct *work, unsigned int cpu)
  {
  	set_work_data(work, cpu << WORK_STRUCT_FLAG_BITS, WORK_STRUCT_PENDING);
  }

  static void clear_work_data(struct work_struct *work)

  {

  	set_work_data(work, WORK_STRUCT_NO_CPU, 0);

  }

  static struct cpu_workqueue_struct *get_work_cwq(struct work_struct *work)

  {

  	unsigned long data = atomic_long_read(&work->data);

  	if (data & WORK_STRUCT_CWQ)
  		return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
  	else
  		return NULL;

  }

  static struct global_cwq *get_work_gcwq(struct work_struct *work)

  {

  	unsigned long data = atomic_long_read(&work->data);

  	unsigned int cpu;

  	if (data & WORK_STRUCT_CWQ)
  		return ((struct cpu_workqueue_struct *)
  			(data & WORK_STRUCT_WQ_DATA_MASK))->gcwq;

  
  	cpu = data >> WORK_STRUCT_FLAG_BITS;

  	if (cpu == WORK_CPU_NONE)

  		return NULL;

  	BUG_ON(cpu >= nr_cpu_ids && cpu != WORK_CPU_UNBOUND);

  	return get_gcwq(cpu);

  }

  /*
   * Policy functions.  These define the policies on how the global
   * worker pool is managed.  Unless noted otherwise, these functions
   * assume that they're being called with gcwq->lock held.
   */

  static bool __need_more_worker(struct global_cwq *gcwq)

  {

  	return !atomic_read(get_gcwq_nr_running(gcwq->cpu)) ||
  		gcwq->flags & GCWQ_HIGHPRI_PENDING;

  }

  /*

   * Need to wake up a worker?  Called from anything but currently
   * running workers.

   */

  static bool need_more_worker(struct global_cwq *gcwq)

  {

  	return !list_empty(&gcwq->worklist) && __need_more_worker(gcwq);

  }

  /* Can I start working?  Called from busy but !running workers. */
  static bool may_start_working(struct global_cwq *gcwq)
  {
  	return gcwq->nr_idle;
  }
  
  /* Do I need to keep working?  Called from currently running workers. */
  static bool keep_working(struct global_cwq *gcwq)
  {
  	atomic_t *nr_running = get_gcwq_nr_running(gcwq->cpu);

  	return !list_empty(&gcwq->worklist) &&
  		(atomic_read(nr_running) <= 1 ||
  		 gcwq->flags & GCWQ_HIGHPRI_PENDING);

  }
  
  /* Do we need a new worker?  Called from manager. */
  static bool need_to_create_worker(struct global_cwq *gcwq)
  {
  	return need_more_worker(gcwq) && !may_start_working(gcwq);
  }

  /* Do I need to be the manager? */
  static bool need_to_manage_workers(struct global_cwq *gcwq)
  {
  	return need_to_create_worker(gcwq) || gcwq->flags & GCWQ_MANAGE_WORKERS;
  }
  
  /* Do we have too many workers and should some go away? */
  static bool too_many_workers(struct global_cwq *gcwq)
  {
  	bool managing = gcwq->flags & GCWQ_MANAGING_WORKERS;
  	int nr_idle = gcwq->nr_idle + managing; /* manager is considered idle */
  	int nr_busy = gcwq->nr_workers - nr_idle;
  
  	return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;

  }

  /*

   * Wake up functions.
   */

  /* Return the first worker.  Safe with preemption disabled */
  static struct worker *first_worker(struct global_cwq *gcwq)
  {
  	if (unlikely(list_empty(&gcwq->idle_list)))
  		return NULL;
  
  	return list_first_entry(&gcwq->idle_list, struct worker, entry);
  }
  
  /**
   * wake_up_worker - wake up an idle worker
   * @gcwq: gcwq to wake worker for
   *
   * Wake up the first idle worker of @gcwq.
   *
   * CONTEXT:
   * spin_lock_irq(gcwq->lock).
   */
  static void wake_up_worker(struct global_cwq *gcwq)
  {
  	struct worker *worker = first_worker(gcwq);
  
  	if (likely(worker))
  		wake_up_process(worker->task);
  }

  /**

   * wq_worker_waking_up - a worker is waking up
   * @task: task waking up
   * @cpu: CPU @task is waking up to
   *
   * This function is called during try_to_wake_up() when a worker is
   * being awoken.
   *
   * CONTEXT:
   * spin_lock_irq(rq->lock)
   */
  void wq_worker_waking_up(struct task_struct *task, unsigned int cpu)
  {
  	struct worker *worker = kthread_data(task);

  	if (!(worker->flags & WORKER_NOT_RUNNING))

  		atomic_inc(get_gcwq_nr_running(cpu));
  }
  
  /**
   * wq_worker_sleeping - a worker is going to sleep
   * @task: task going to sleep
   * @cpu: CPU in question, must be the current CPU number
   *
   * This function is called during schedule() when a busy worker is
   * going to sleep.  Worker on the same cpu can be woken up by
   * returning pointer to its task.
   *
   * CONTEXT:
   * spin_lock_irq(rq->lock)
   *
   * RETURNS:
   * Worker task on @cpu to wake up, %NULL if none.
   */
  struct task_struct *wq_worker_sleeping(struct task_struct *task,
  				       unsigned int cpu)
  {
  	struct worker *worker = kthread_data(task), *to_wakeup = NULL;
  	struct global_cwq *gcwq = get_gcwq(cpu);
  	atomic_t *nr_running = get_gcwq_nr_running(cpu);

  	if (worker->flags & WORKER_NOT_RUNNING)

  		return NULL;
  
  	/* this can only happen on the local cpu */
  	BUG_ON(cpu != raw_smp_processor_id());
  
  	/*
  	 * The counterpart of the following dec_and_test, implied mb,
  	 * worklist not empty test sequence is in insert_work().
  	 * Please read comment there.
  	 *
  	 * NOT_RUNNING is clear.  This means that trustee is not in
  	 * charge and we're running on the local cpu w/ rq lock held
  	 * and preemption disabled, which in turn means that none else
  	 * could be manipulating idle_list, so dereferencing idle_list
  	 * without gcwq lock is safe.
  	 */
  	if (atomic_dec_and_test(nr_running) && !list_empty(&gcwq->worklist))
  		to_wakeup = first_worker(gcwq);
  	return to_wakeup ? to_wakeup->task : NULL;
  }
  
  /**
   * worker_set_flags - set worker flags and adjust nr_running accordingly

   * @worker: self

   * @flags: flags to set
   * @wakeup: wakeup an idle worker if necessary
   *

   * Set @flags in @worker->flags and adjust nr_running accordingly.  If
   * nr_running becomes zero and @wakeup is %true, an idle worker is
   * woken up.

   *

   * CONTEXT:
   * spin_lock_irq(gcwq->lock)

   */
  static inline void worker_set_flags(struct worker *worker, unsigned int flags,
  				    bool wakeup)
  {

  	struct global_cwq *gcwq = worker->gcwq;

  	WARN_ON_ONCE(worker->task != current);

  	/*
  	 * If transitioning into NOT_RUNNING, adjust nr_running and
  	 * wake up an idle worker as necessary if requested by
  	 * @wakeup.
  	 */
  	if ((flags & WORKER_NOT_RUNNING) &&
  	    !(worker->flags & WORKER_NOT_RUNNING)) {
  		atomic_t *nr_running = get_gcwq_nr_running(gcwq->cpu);
  
  		if (wakeup) {
  			if (atomic_dec_and_test(nr_running) &&
  			    !list_empty(&gcwq->worklist))
  				wake_up_worker(gcwq);
  		} else
  			atomic_dec(nr_running);
  	}

  	worker->flags |= flags;
  }
  
  /**

   * worker_clr_flags - clear worker flags and adjust nr_running accordingly

   * @worker: self

   * @flags: flags to clear
   *

   * Clear @flags in @worker->flags and adjust nr_running accordingly.

   *

   * CONTEXT:
   * spin_lock_irq(gcwq->lock)

   */
  static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
  {

  	struct global_cwq *gcwq = worker->gcwq;
  	unsigned int oflags = worker->flags;

  	WARN_ON_ONCE(worker->task != current);

  	worker->flags &= ~flags;

  	/*
  	 * If transitioning out of NOT_RUNNING, increment nr_running.  Note
  	 * that the nested NOT_RUNNING is not a noop.  NOT_RUNNING is mask
  	 * of multiple flags, not a single flag.
  	 */

  	if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
  		if (!(worker->flags & WORKER_NOT_RUNNING))
  			atomic_inc(get_gcwq_nr_running(gcwq->cpu));

  }
  
  /**

   * busy_worker_head - return the busy hash head for a work
   * @gcwq: gcwq of interest
   * @work: work to be hashed
   *
   * Return hash head of @gcwq for @work.
   *
   * CONTEXT:
   * spin_lock_irq(gcwq->lock).
   *
   * RETURNS:
   * Pointer to the hash head.
   */
  static struct hlist_head *busy_worker_head(struct global_cwq *gcwq,
  					   struct work_struct *work)
  {
  	const int base_shift = ilog2(sizeof(struct work_struct));
  	unsigned long v = (unsigned long)work;
  
  	/* simple shift and fold hash, do we need something better? */
  	v >>= base_shift;
  	v += v >> BUSY_WORKER_HASH_ORDER;
  	v &= BUSY_WORKER_HASH_MASK;
  
  	return &gcwq->busy_hash[v];
  }
  
  /**

   * __find_worker_executing_work - find worker which is executing a work
   * @gcwq: gcwq of interest
   * @bwh: hash head as returned by busy_worker_head()
   * @work: work to find worker for
   *
   * Find a worker which is executing @work on @gcwq.  @bwh should be
   * the hash head obtained by calling busy_worker_head() with the same
   * work.
   *
   * CONTEXT:
   * spin_lock_irq(gcwq->lock).
   *
   * RETURNS:
   * Pointer to worker which is executing @work if found, NULL
   * otherwise.
   */
  static struct worker *__find_worker_executing_work(struct global_cwq *gcwq,
  						   struct hlist_head *bwh,
  						   struct work_struct *work)
  {
  	struct worker *worker;
  	struct hlist_node *tmp;
  
  	hlist_for_each_entry(worker, tmp, bwh, hentry)
  		if (worker->current_work == work)
  			return worker;
  	return NULL;
  }
  
  /**
   * find_worker_executing_work - find worker which is executing a work
   * @gcwq: gcwq of interest
   * @work: work to find worker for
   *
   * Find a worker which is executing @work on @gcwq.  This function is
   * identical to __find_worker_executing_work() except that this
   * function calculates @bwh itself.
   *
   * CONTEXT:
   * spin_lock_irq(gcwq->lock).
   *
   * RETURNS:
   * Pointer to worker which is executing @work if found, NULL
   * otherwise.

   */

  static struct worker *find_worker_executing_work(struct global_cwq *gcwq,
  						 struct work_struct *work)

  {

  	return __find_worker_executing_work(gcwq, busy_worker_head(gcwq, work),
  					    work);

  }

  /**

   * gcwq_determine_ins_pos - find insertion position
   * @gcwq: gcwq of interest
   * @cwq: cwq a work is being queued for
   *
   * A work for @cwq is about to be queued on @gcwq, determine insertion
   * position for the work.  If @cwq is for HIGHPRI wq, the work is
   * queued at the head of the queue but in FIFO order with respect to
   * other HIGHPRI works; otherwise, at the end of the queue.  This
   * function also sets GCWQ_HIGHPRI_PENDING flag to hint @gcwq that
   * there are HIGHPRI works pending.
   *
   * CONTEXT:
   * spin_lock_irq(gcwq->lock).
   *
   * RETURNS:
   * Pointer to inserstion position.
   */
  static inline struct list_head *gcwq_determine_ins_pos(struct global_cwq *gcwq,
  					       struct cpu_workqueue_struct *cwq)

  {

  	struct work_struct *twork;
  
  	if (likely(!(cwq->wq->flags & WQ_HIGHPRI)))
  		return &gcwq->worklist;
  
  	list_for_each_entry(twork, &gcwq->worklist, entry) {
  		struct cpu_workqueue_struct *tcwq = get_work_cwq(twork);
  
  		if (!(tcwq->wq->flags & WQ_HIGHPRI))
  			break;
  	}
  
  	gcwq->flags |= GCWQ_HIGHPRI_PENDING;
  	return &twork->entry;

  }

  /**

   * insert_work - insert a work into gcwq

   * @cwq: cwq @work belongs to
   * @work: work to insert
   * @head: insertion point
   * @extra_flags: extra WORK_STRUCT_* flags to set
   *

   * Insert @work which belongs to @cwq into @gcwq after @head.
   * @extra_flags is or'd to work_struct flags.

   *
   * CONTEXT:

   * spin_lock_irq(gcwq->lock).

   */

  static void insert_work(struct cpu_workqueue_struct *cwq,

  			struct work_struct *work, struct list_head *head,
  			unsigned int extra_flags)

  {

  	struct global_cwq *gcwq = cwq->gcwq;

  	/* we own @work, set data and link */

  	set_work_cwq(work, cwq, extra_flags);

  	/*
  	 * Ensure that we get the right work->data if we see the
  	 * result of list_add() below, see try_to_grab_pending().
  	 */
  	smp_wmb();

  	list_add_tail(&work->entry, head);

  
  	/*
  	 * Ensure either worker_sched_deactivated() sees the above
  	 * list_add_tail() or we see zero nr_running to avoid workers
  	 * lying around lazily while there are works to be processed.
  	 */
  	smp_mb();

  	if (__need_more_worker(gcwq))

  		wake_up_worker(gcwq);

  }

  /*
   * Test whether @work is being queued from another work executing on the
   * same workqueue.  This is rather expensive and should only be used from
   * cold paths.
   */
  static bool is_chained_work(struct workqueue_struct *wq)
  {
  	unsigned long flags;
  	unsigned int cpu;
  
  	for_each_gcwq_cpu(cpu) {
  		struct global_cwq *gcwq = get_gcwq(cpu);
  		struct worker *worker;
  		struct hlist_node *pos;
  		int i;
  
  		spin_lock_irqsave(&gcwq->lock, flags);
  		for_each_busy_worker(worker, i, pos, gcwq) {
  			if (worker->task != current)
  				continue;
  			spin_unlock_irqrestore(&gcwq->lock, flags);
  			/*
  			 * I'm @worker, no locking necessary.  See if @work
  			 * is headed to the same workqueue.
  			 */
  			return worker->current_cwq->wq == wq;
  		}
  		spin_unlock_irqrestore(&gcwq->lock, flags);
  	}
  	return false;
  }

  static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,

  			 struct work_struct *work)
  {

  	struct global_cwq *gcwq;
  	struct cpu_workqueue_struct *cwq;

  	struct list_head *worklist;

  	unsigned int work_flags;

  	unsigned long flags;

  	debug_work_activate(work);

  	/* if dying, only works from the same workqueue are allowed */

  	if (unlikely(wq->flags & WQ_DRAINING) &&

  	    WARN_ON_ONCE(!is_chained_work(wq)))

  		return;

  	/* determine gcwq to use */
  	if (!(wq->flags & WQ_UNBOUND)) {

  		struct global_cwq *last_gcwq;

  		if (unlikely(cpu == WORK_CPU_UNBOUND))
  			cpu = raw_smp_processor_id();

  		/*
  		 * It's multi cpu.  If @wq is non-reentrant and @work
  		 * was previously on a different cpu, it might still
  		 * be running there, in which case the work needs to
  		 * be queued on that cpu to guarantee non-reentrance.
  		 */

  		gcwq = get_gcwq(cpu);

  		if (wq->flags & WQ_NON_REENTRANT &&
  		    (last_gcwq = get_work_gcwq(work)) && last_gcwq != gcwq) {
  			struct worker *worker;
  
  			spin_lock_irqsave(&last_gcwq->lock, flags);
  
  			worker = find_worker_executing_work(last_gcwq, work);
  
  			if (worker && worker->current_cwq->wq == wq)
  				gcwq = last_gcwq;
  			else {
  				/* meh... not running there, queue here */
  				spin_unlock_irqrestore(&last_gcwq->lock, flags);
  				spin_lock_irqsave(&gcwq->lock, flags);
  			}
  		} else
  			spin_lock_irqsave(&gcwq->lock, flags);

  	} else {
  		gcwq = get_gcwq(WORK_CPU_UNBOUND);
  		spin_lock_irqsave(&gcwq->lock, flags);

  	}
  
  	/* gcwq determined, get cwq and queue */
  	cwq = get_cwq(gcwq->cpu, wq);

  	trace_workqueue_queue_work(cpu, cwq, work);

  	if (WARN_ON(!list_empty(&work->entry))) {
  		spin_unlock_irqrestore(&gcwq->lock, flags);
  		return;
  	}

  	cwq->nr_in_flight[cwq->work_color]++;

  	work_flags = work_color_to_flags(cwq->work_color);

  
  	if (likely(cwq->nr_active < cwq->max_active)) {

  		trace_workqueue_activate_work(work);

  		cwq->nr_active++;

  		worklist = gcwq_determine_ins_pos(gcwq, cwq);

  	} else {
  		work_flags |= WORK_STRUCT_DELAYED;

  		worklist = &cwq->delayed_works;

  	}

  	insert_work(cwq, work, worklist, work_flags);

  	spin_unlock_irqrestore(&gcwq->lock, flags);

  }

  /**
   * queue_work - queue work on a workqueue
   * @wq: workqueue to use
   * @work: work to queue
   *

   * Returns 0 if @work was already on a queue, non-zero otherwise.

   *

   * We queue the work to the CPU on which it was submitted, but if the CPU dies
   * it can be processed by another CPU.

   */

  int queue_work(struct workqueue_struct *wq, struct work_struct *work)

  {

  	int ret;
  
  	ret = queue_work_on(get_cpu(), wq, work);
  	put_cpu();

  	return ret;
  }

  EXPORT_SYMBOL_GPL(queue_work);

  /**
   * queue_work_on - queue work on specific cpu
   * @cpu: CPU number to execute work on
   * @wq: workqueue to use
   * @work: work to queue
   *
   * Returns 0 if @work was already on a queue, non-zero otherwise.
   *
   * We queue the work to a specific CPU, the caller must ensure it
   * can't go away.
   */
  int
  queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
  {
  	int ret = 0;

  	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {

  		__queue_work(cpu, wq, work);

  		ret = 1;
  	}
  	return ret;
  }
  EXPORT_SYMBOL_GPL(queue_work_on);

  static void delayed_work_timer_fn(unsigned long __data)

  {

  	struct delayed_work *dwork = (struct delayed_work *)__data;

  	struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);

  	__queue_work(smp_processor_id(), cwq->wq, &dwork->work);

  }

  /**
   * queue_delayed_work - queue work on a workqueue after delay
   * @wq: workqueue to use

   * @dwork: delayable work to queue

   * @delay: number of jiffies to wait before queueing
   *

   * Returns 0 if @work was already on a queue, non-zero otherwise.

   */

  int queue_delayed_work(struct workqueue_struct *wq,

  			struct delayed_work *dwork, unsigned long delay)

  {

  	if (delay == 0)

  		return queue_work(wq, &dwork->work);

  	return queue_delayed_work_on(-1, wq, dwork, delay);

  }

  EXPORT_SYMBOL_GPL(queue_delayed_work);

  /**
   * queue_delayed_work_on - queue work on specific CPU after delay
   * @cpu: CPU number to execute work on
   * @wq: workqueue to use

   * @dwork: work to queue

   * @delay: number of jiffies to wait before queueing
   *

   * Returns 0 if @work was already on a queue, non-zero otherwise.

   */

  int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,

  			struct delayed_work *dwork, unsigned long delay)

  {
  	int ret = 0;

  	struct timer_list *timer = &dwork->timer;
  	struct work_struct *work = &dwork->work;

  	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {

  		unsigned int lcpu;

  		BUG_ON(timer_pending(timer));
  		BUG_ON(!list_empty(&work->entry));

  		timer_stats_timer_set_start_info(&dwork->timer);

  		/*
  		 * This stores cwq for the moment, for the timer_fn.
  		 * Note that the work's gcwq is preserved to allow
  		 * reentrance detection for delayed works.
  		 */

  		if (!(wq->flags & WQ_UNBOUND)) {
  			struct global_cwq *gcwq = get_work_gcwq(work);
  
  			if (gcwq && gcwq->cpu != WORK_CPU_UNBOUND)
  				lcpu = gcwq->cpu;
  			else
  				lcpu = raw_smp_processor_id();
  		} else
  			lcpu = WORK_CPU_UNBOUND;

  		set_work_cwq(work, get_cwq(lcpu, wq), 0);

  		timer->expires = jiffies + delay;

  		timer->data = (unsigned long)dwork;

  		timer->function = delayed_work_timer_fn;

  
  		if (unlikely(cpu >= 0))
  			add_timer_on(timer, cpu);
  		else
  			add_timer(timer);

  		ret = 1;
  	}
  	return ret;
  }

  EXPORT_SYMBOL_GPL(queue_delayed_work_on);

  /**
   * worker_enter_idle - enter idle state
   * @worker: worker which is entering idle state
   *
   * @worker is entering idle state.  Update stats and idle timer if
   * necessary.
   *
   * LOCKING:
   * spin_lock_irq(gcwq->lock).
   */
  static void worker_enter_idle(struct worker *worker)

  {

  	struct global_cwq *gcwq = worker->gcwq;
  
  	BUG_ON(worker->flags & WORKER_IDLE);
  	BUG_ON(!list_empty(&worker->entry) &&
  	       (worker->hentry.next || worker->hentry.pprev));

  	/* can't use worker_set_flags(), also called from start_worker() */
  	worker->flags |= WORKER_IDLE;

  	gcwq->nr_idle++;

  	worker->last_active = jiffies;

  
  	/* idle_list is LIFO */
  	list_add(&worker->entry, &gcwq->idle_list);

  	if (likely(!(worker->flags & WORKER_ROGUE))) {
  		if (too_many_workers(gcwq) && !timer_pending(&gcwq->idle_timer))
  			mod_timer(&gcwq->idle_timer,
  				  jiffies + IDLE_WORKER_TIMEOUT);
  	} else

  		wake_up_all(&gcwq->trustee_wait);

  	/*
  	 * Sanity check nr_running.  Because trustee releases gcwq->lock
  	 * between setting %WORKER_ROGUE and zapping nr_running, the
  	 * warning may trigger spuriously.  Check iff trustee is idle.
  	 */
  	WARN_ON_ONCE(gcwq->trustee_state == TRUSTEE_DONE &&
  		     gcwq->nr_workers == gcwq->nr_idle &&

  		     atomic_read(get_gcwq_nr_running(gcwq->cpu)));

  }
  
  /**
   * worker_leave_idle - leave idle state
   * @worker: worker which is leaving idle state
   *
   * @worker is leaving idle state.  Update stats.
   *
   * LOCKING:
   * spin_lock_irq(gcwq->lock).
   */
  static void worker_leave_idle(struct worker *worker)
  {
  	struct global_cwq *gcwq = worker->gcwq;
  
  	BUG_ON(!(worker->flags & WORKER_IDLE));

  	worker_clr_flags(worker, WORKER_IDLE);

  	gcwq->nr_idle--;
  	list_del_init(&worker->entry);
  }

  /**
   * worker_maybe_bind_and_lock - bind worker to its cpu if possible and lock gcwq
   * @worker: self
   *
   * Works which are scheduled while the cpu is online must at least be
   * scheduled to a worker which is bound to the cpu so that if they are
   * flushed from cpu callbacks while cpu is going down, they are
   * guaranteed to execute on the cpu.
   *
   * This function is to be used by rogue workers and rescuers to bind
   * themselves to the target cpu and may race with cpu going down or
   * coming online.  kthread_bind() can't be used because it may put the
   * worker to already dead cpu and set_cpus_allowed_ptr() can't be used
   * verbatim as it's best effort and blocking and gcwq may be
   * [dis]associated in the meantime.
   *
   * This function tries set_cpus_allowed() and locks gcwq and verifies
   * the binding against GCWQ_DISASSOCIATED which is set during
   * CPU_DYING and cleared during CPU_ONLINE, so if the worker enters
   * idle state or fetches works without dropping lock, it can guarantee
   * the scheduling requirement described in the first paragraph.
   *
   * CONTEXT:
   * Might sleep.  Called without any lock but returns with gcwq->lock
   * held.
   *
   * RETURNS:
   * %true if the associated gcwq is online (@worker is successfully
   * bound), %false if offline.
   */
  static bool worker_maybe_bind_and_lock(struct worker *worker)

  __acquires(&gcwq->lock)

  {
  	struct global_cwq *gcwq = worker->gcwq;
  	struct task_struct *task = worker->task;
  
  	while (true) {

  		/*

  		 * The following call may fail, succeed or succeed
  		 * without actually migrating the task to the cpu if
  		 * it races with cpu hotunplug operation.  Verify
  		 * against GCWQ_DISASSOCIATED.

  		 */

  		if (!(gcwq->flags & GCWQ_DISASSOCIATED))
  			set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu));

  
  		spin_lock_irq(&gcwq->lock);
  		if (gcwq->flags & GCWQ_DISASSOCIATED)
  			return false;
  		if (task_cpu(task) == gcwq->cpu &&
  		    cpumask_equal(&current->cpus_allowed,
  				  get_cpu_mask(gcwq->cpu)))
  			return true;
  		spin_unlock_irq(&gcwq->lock);

  		/*
  		 * We've raced with CPU hot[un]plug.  Give it a breather
  		 * and retry migration.  cond_resched() is required here;
  		 * otherwise, we might deadlock against cpu_stop trying to
  		 * bring down the CPU on non-preemptive kernel.
  		 */

  		cpu_relax();

  		cond_resched();

  	}
  }
  
  /*
   * Function for worker->rebind_work used to rebind rogue busy workers
   * to the associated cpu which is coming back online.  This is
   * scheduled by cpu up but can race with other cpu hotplug operations
   * and may be executed twice without intervening cpu down.
   */
  static void worker_rebind_fn(struct work_struct *work)
  {
  	struct worker *worker = container_of(work, struct worker, rebind_work);
  	struct global_cwq *gcwq = worker->gcwq;
  
  	if (worker_maybe_bind_and_lock(worker))
  		worker_clr_flags(worker, WORKER_REBIND);
  
  	spin_unlock_irq(&gcwq->lock);
  }

  static struct worker *alloc_worker(void)
  {
  	struct worker *worker;
  
  	worker = kzalloc(sizeof(*worker), GFP_KERNEL);

  	if (worker) {
  		INIT_LIST_HEAD(&worker->entry);

  		INIT_LIST_HEAD(&worker->scheduled);

  		INIT_WORK(&worker->rebind_work, worker_rebind_fn);
  		/* on creation a worker is in !idle && prep state */
  		worker->flags = WORKER_PREP;

  	}

  	return worker;
  }
  
  /**
   * create_worker - create a new workqueue worker

   * @gcwq: gcwq the new worker will belong to

   * @bind: whether to set affinity to @cpu or not
   *

   * Create a new worker which is bound to @gcwq.  The returned worker

   * can be started by calling start_worker() or destroyed using
   * destroy_worker().
   *
   * CONTEXT:
   * Might sleep.  Does GFP_KERNEL allocations.
   *
   * RETURNS:
   * Pointer to the newly created worker.
   */

  static struct worker *create_worker(struct global_cwq *gcwq, bool bind)

  {

  	bool on_unbound_cpu = gcwq->cpu == WORK_CPU_UNBOUND;

  	struct worker *worker = NULL;

  	int id = -1;

  	spin_lock_irq(&gcwq->lock);
  	while (ida_get_new(&gcwq->worker_ida, &id)) {
  		spin_unlock_irq(&gcwq->lock);
  		if (!ida_pre_get(&gcwq->worker_ida, GFP_KERNEL))

  			goto fail;

  		spin_lock_irq(&gcwq->lock);

  	}

  	spin_unlock_irq(&gcwq->lock);

  
  	worker = alloc_worker();
  	if (!worker)
  		goto fail;

  	worker->gcwq = gcwq;

  	worker->id = id;

  	if (!on_unbound_cpu)

  		worker->task = kthread_create_on_node(worker_thread,
  						      worker,
  						      cpu_to_node(gcwq->cpu),
  						      "kworker/%u:%d", gcwq->cpu, id);

  	else
  		worker->task = kthread_create(worker_thread, worker,
  					      "kworker/u:%d", id);

  	if (IS_ERR(worker->task))
  		goto fail;

  	/*
  	 * A rogue worker will become a regular one if CPU comes
  	 * online later on.  Make sure every worker has
  	 * PF_THREAD_BOUND set.
  	 */

  	if (bind && !on_unbound_cpu)

  		kthread_bind(worker->task, gcwq->cpu);

  	else {

  		worker->task->flags |= PF_THREAD_BOUND;

  		if (on_unbound_cpu)
  			worker->flags |= WORKER_UNBOUND;
  	}

  
  	return worker;
  fail:
  	if (id >= 0) {

  		spin_lock_irq(&gcwq->lock);
  		ida_remove(&gcwq->worker_ida, id);
  		spin_unlock_irq(&gcwq->lock);

  	}
  	kfree(worker);
  	return NULL;
  }
  
  /**
   * start_worker - start a newly created worker
   * @worker: worker to start
   *

   * Make the gcwq aware of @worker and start it.

   *
   * CONTEXT:

   * spin_lock_irq(gcwq->lock).

   */
  static void start_worker(struct worker *worker)
  {

  	worker->flags |= WORKER_STARTED;

  	worker->gcwq->nr_workers++;
  	worker_enter_idle(worker);

  	wake_up_process(worker->task);
  }
  
  /**
   * destroy_worker - destroy a workqueue worker
   * @worker: worker to be destroyed
   *

   * Destroy @worker and adjust @gcwq stats accordingly.
   *
   * CONTEXT:
   * spin_lock_irq(gcwq->lock) which is released and regrabbed.

   */
  static void destroy_worker(struct worker *worker)
  {

  	struct global_cwq *gcwq = worker->gcwq;

  	int id = worker->id;
  
  	/* sanity check frenzy */
  	BUG_ON(worker->current_work);

  	BUG_ON(!list_empty(&worker->scheduled));

  	if (worker->flags & WORKER_STARTED)
  		gcwq->nr_workers--;
  	if (worker->flags & WORKER_IDLE)
  		gcwq->nr_idle--;
  
  	list_del_init(&worker->entry);

  	worker->flags |= WORKER_DIE;

  
  	spin_unlock_irq(&gcwq->lock);

  	kthread_stop(worker->task);
  	kfree(worker);

  	spin_lock_irq(&gcwq->lock);
  	ida_remove(&gcwq->worker_ida, id);

  }

  static void idle_worker_timeout(unsigned long __gcwq)
  {
  	struct global_cwq *gcwq = (void *)__gcwq;
  
  	spin_lock_irq(&gcwq->lock);
  
  	if (too_many_workers(gcwq)) {
  		struct worker *worker;
  		unsigned long expires;
  
  		/* idle_list is kept in LIFO order, check the last one */
  		worker = list_entry(gcwq->idle_list.prev, struct worker, entry);
  		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
  
  		if (time_before(jiffies, expires))
  			mod_timer(&gcwq->idle_timer, expires);
  		else {
  			/* it's been idle for too long, wake up manager */
  			gcwq->flags |= GCWQ_MANAGE_WORKERS;
  			wake_up_worker(gcwq);

  		}

  	}
  
  	spin_unlock_irq(&gcwq->lock);
  }

  static bool send_mayday(struct work_struct *work)
  {
  	struct cpu_workqueue_struct *cwq = get_work_cwq(work);
  	struct workqueue_struct *wq = cwq->wq;

  	unsigned int cpu;

  
  	if (!(wq->flags & WQ_RESCUER))
  		return false;
  
  	/* mayday mayday mayday */

  	cpu = cwq->gcwq->cpu;
  	/* WORK_CPU_UNBOUND can't be set in cpumask, use cpu 0 instead */
  	if (cpu == WORK_CPU_UNBOUND)
  		cpu = 0;

  	if (!mayday_test_and_set_cpu(cpu, wq->mayday_mask))

  		wake_up_process(wq->rescuer->task);
  	return true;
  }
  
  static void gcwq_mayday_timeout(unsigned long __gcwq)
  {
  	struct global_cwq *gcwq = (void *)__gcwq;
  	struct work_struct *work;
  
  	spin_lock_irq(&gcwq->lock);
  
  	if (need_to_create_worker(gcwq)) {
  		/*
  		 * We've been trying to create a new worker but
  		 * haven't been successful.  We might be hitting an
  		 * allocation deadlock.  Send distress signals to
  		 * rescuers.
  		 */
  		list_for_each_entry(work, &gcwq->worklist, entry)
  			send_mayday(work);

  	}

  
  	spin_unlock_irq(&gcwq->lock);
  
  	mod_timer(&gcwq->mayday_timer, jiffies + MAYDAY_INTERVAL);

  }

  /**
   * maybe_create_worker - create a new worker if necessary
   * @gcwq: gcwq to create a new worker for
   *
   * Create a new worker for @gcwq if necessary.  @gcwq is guaranteed to
   * have at least one idle worker on return from this function.  If
   * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
   * sent to all rescuers with works scheduled on @gcwq to resolve
   * possible allocation deadlock.
   *
   * On return, need_to_create_worker() is guaranteed to be false and
   * may_start_working() true.
   *
   * LOCKING:
   * spin_lock_irq(gcwq->lock) which may be released and regrabbed
   * multiple times.  Does GFP_KERNEL allocations.  Called only from
   * manager.
   *
   * RETURNS:
   * false if no action was taken and gcwq->lock stayed locked, true
   * otherwise.
   */
  static bool maybe_create_worker(struct global_cwq *gcwq)

  __releases(&gcwq->lock)
  __acquires(&gcwq->lock)

  {

  	if (!need_to_create_worker(gcwq))
  		return false;
  restart:

  	spin_unlock_irq(&gcwq->lock);

  	/* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
  	mod_timer(&gcwq->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);
  
  	while (true) {
  		struct worker *worker;

  		worker = create_worker(gcwq, true);
  		if (worker) {
  			del_timer_sync(&gcwq->mayday_timer);
  			spin_lock_irq(&gcwq->lock);
  			start_worker(worker);
  			BUG_ON(need_to_create_worker(gcwq));
  			return true;
  		}
  
  		if (!need_to_create_worker(gcwq))
  			break;

  		__set_current_state(TASK_INTERRUPTIBLE);
  		schedule_timeout(CREATE_COOLDOWN);

  		if (!need_to_create_worker(gcwq))
  			break;
  	}

  	del_timer_sync(&gcwq->mayday_timer);
  	spin_lock_irq(&gcwq->lock);
  	if (need_to_create_worker(gcwq))
  		goto restart;
  	return true;
  }
  
  /**
   * maybe_destroy_worker - destroy workers which have been idle for a while
   * @gcwq: gcwq to destroy workers for
   *
   * Destroy @gcwq workers which have been idle for longer than
   * IDLE_WORKER_TIMEOUT.
   *
   * LOCKING:
   * spin_lock_irq(gcwq->lock) which may be released and regrabbed
   * multiple times.  Called only from manager.
   *
   * RETURNS:
   * false if no action was taken and gcwq->lock stayed locked, true
   * otherwise.
   */
  static bool maybe_destroy_workers(struct global_cwq *gcwq)
  {
  	bool ret = false;

  	while (too_many_workers(gcwq)) {
  		struct worker *worker;
  		unsigned long expires;

  		worker = list_entry(gcwq->idle_list.prev, struct worker, entry);
  		expires = worker->last_active + IDLE_WORKER_TIMEOUT;

  		if (time_before(jiffies, expires)) {
  			mod_timer(&gcwq->idle_timer, expires);

  			break;

  		}

  		destroy_worker(worker);
  		ret = true;

  	}

  	return ret;
  }
  
  /**
   * manage_workers - manage worker pool
   * @worker: self
   *
   * Assume the manager role and manage gcwq worker pool @worker belongs
   * to.  At any given time, there can be only zero or one manager per
   * gcwq.  The exclusion is handled automatically by this function.
   *
   * The caller can safely start processing works on false return.  On
   * true return, it's guaranteed that need_to_create_worker() is false
   * and may_start_working() is true.
   *
   * CONTEXT:
   * spin_lock_irq(gcwq->lock) which may be released and regrabbed
   * multiple times.  Does GFP_KERNEL allocations.
   *
   * RETURNS:
   * false if no action was taken and gcwq->lock stayed locked, true if
   * some action was taken.
   */
  static bool manage_workers(struct worker *worker)
  {
  	struct global_cwq *gcwq = worker->gcwq;
  	bool ret = false;
  
  	if (gcwq->flags & GCWQ_MANAGING_WORKERS)
  		return ret;
  
  	gcwq->flags &= ~GCWQ_MANAGE_WORKERS;
  	gcwq->flags |= GCWQ_MANAGING_WORKERS;
  
  	/*
  	 * Destroy and then create so that may_start_working() is true
  	 * on return.
  	 */
  	ret |= maybe_destroy_workers(gcwq);
  	ret |= maybe_create_worker(gcwq);
  
  	gcwq->flags &= ~GCWQ_MANAGING_WORKERS;
  
  	/*
  	 * The trustee might be waiting to take over the manager
  	 * position, tell it we're done.
  	 */
  	if (unlikely(gcwq->trustee))
  		wake_up_all(&gcwq->trustee_wait);
  
  	return ret;
  }

  /**

   * move_linked_works - move linked works to a list
   * @work: start of series of works to be scheduled
   * @head: target list to append @work to
   * @nextp: out paramter for nested worklist walking
   *
   * Schedule linked works starting from @work to @head.  Work series to
   * be scheduled starts at @work and includes any consecutive work with
   * WORK_STRUCT_LINKED set in its predecessor.
   *
   * If @nextp is not NULL, it's updated to point to the next work of
   * the last scheduled work.  This allows move_linked_works() to be
   * nested inside outer list_for_each_entry_safe().
   *
   * CONTEXT:

   * spin_lock_irq(gcwq->lock).

   */
  static void move_linked_works(struct work_struct *work, struct list_head *head,
  			      struct work_struct **nextp)
  {
  	struct work_struct *n;
  
  	/*
  	 * Linked worklist will always end before the end of the list,
  	 * use NULL for list head.
  	 */
  	list_for_each_entry_safe_from(work, n, NULL, entry) {
  		list_move_tail(&work->entry, head);
  		if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
  			break;
  	}
  
  	/*
  	 * If we're already inside safe list traversal and have moved
  	 * multiple works to the scheduled queue, the next position
  	 * needs to be updated.
  	 */
  	if (nextp)
  		*nextp = n;
  }

  static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq)
  {
  	struct work_struct *work = list_first_entry(&cwq->delayed_works,
  						    struct work_struct, entry);

  	struct list_head *pos = gcwq_determine_ins_pos(cwq->gcwq, cwq);

  	trace_workqueue_activate_work(work);

  	move_linked_works(work, pos, NULL);

  	__clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));

  	cwq->nr_active++;
  }

  /**

   * cwq_dec_nr_in_flight - decrement cwq's nr_in_flight
   * @cwq: cwq of interest
   * @color: color of work which left the queue

   * @delayed: for a delayed work

   *
   * A work either has completed or is removed from pending queue,
   * decrement nr_in_flight of its cwq and handle workqueue flushing.
   *
   * CONTEXT:

   * spin_lock_irq(gcwq->lock).

   */

  static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color,
  				 bool delayed)

  {
  	/* ignore uncolored works */
  	if (color == WORK_NO_COLOR)
  		return;
  
  	cwq->nr_in_flight[color]--;

  	if (!delayed) {
  		cwq->nr_active--;
  		if (!list_empty(&cwq->delayed_works)) {
  			/* one down, submit a delayed one */
  			if (cwq->nr_active < cwq->max_active)
  				cwq_activate_first_delayed(cwq);
  		}

  	}

  
  	/* is flush in progress and are we at the flushing tip? */
  	if (likely(cwq->flush_color != color))
  		return;
  
  	/* are there still in-flight works? */
  	if (cwq->nr_in_flight[color])
  		return;
  
  	/* this cwq is done, clear flush_color */
  	cwq->flush_color = -1;
  
  	/*
  	 * If this was the last cwq, wake up the first flusher.  It
  	 * will handle the rest.
  	 */
  	if (atomic_dec_and_test(&cwq->wq->nr_cwqs_to_flush))
  		complete(&cwq->wq->first_flusher->done);
  }
  
  /**

   * process_one_work - process single work

   * @worker: self

   * @work: work to process
   *
   * Process @work.  This function contains all the logics necessary to
   * process a single work including synchronization against and
   * interaction with other workers on the same cpu, queueing and
   * flushing.  As long as context requirement is met, any worker can
   * call this function to process a work.
   *
   * CONTEXT:

   * spin_lock_irq(gcwq->lock) which is released and regrabbed.

   */

  static void process_one_work(struct worker *worker, struct work_struct *work)

  __releases(&gcwq->lock)
  __acquires(&gcwq->lock)

  {

  	struct cpu_workqueue_struct *cwq = get_work_cwq(work);

  	struct global_cwq *gcwq = cwq->gcwq;

  	struct hlist_head *bwh = busy_worker_head(gcwq, work);

  	bool cpu_intensive = cwq->wq->flags & WQ_CPU_INTENSIVE;

  	work_func_t f = work->func;

  	int work_color;

  	struct worker *collision;

  #ifdef CONFIG_LOCKDEP
  	/*
  	 * It is permissible to free the struct work_struct from
  	 * inside the function that is called from it, this we need to
  	 * take into account for lockdep too.  To avoid bogus "held
  	 * lock freed" warnings as well as problems when looking into
  	 * work->lockdep_map, make a copy and use that here.
  	 */

  	struct lockdep_map lockdep_map;
  
  	lockdep_copy_map(&lockdep_map, &work->lockdep_map);

  #endif

  	/*
  	 * A single work shouldn't be executed concurrently by
  	 * multiple workers on a single cpu.  Check whether anyone is
  	 * already processing the work.  If so, defer the work to the
  	 * currently executing one.
  	 */
  	collision = __find_worker_executing_work(gcwq, bwh, work);
  	if (unlikely(collision)) {
  		move_linked_works(work, &collision->scheduled, NULL);
  		return;
  	}

  	/* claim and process */

  	debug_work_deactivate(work);

  	hlist_add_head(&worker->hentry, bwh);

  	worker->current_work = work;

  	worker->current_cwq = cwq;

  	work_color = get_work_color(work);

  	/* record the current cpu number in the work data and dequeue */
  	set_work_cpu(work, gcwq->cpu);

  	list_del_init(&work->entry);

  	/*
  	 * If HIGHPRI_PENDING, check the next work, and, if HIGHPRI,
  	 * wake up another worker; otherwise, clear HIGHPRI_PENDING.
  	 */
  	if (unlikely(gcwq->flags & GCWQ_HIGHPRI_PENDING)) {
  		struct work_struct *nwork = list_first_entry(&gcwq->worklist,
  						struct work_struct, entry);
  
  		if (!list_empty(&gcwq->worklist) &&
  		    get_work_cwq(nwork)->wq->flags & WQ_HIGHPRI)
  			wake_up_worker(gcwq);
  		else
  			gcwq->flags &= ~GCWQ_HIGHPRI_PENDING;
  	}

  	/*
  	 * CPU intensive works don't participate in concurrency
  	 * management.  They're the scheduler's responsibility.
  	 */
  	if (unlikely(cpu_intensive))
  		worker_set_flags(worker, WORKER_CPU_INTENSIVE, true);

  	spin_unlock_irq(&gcwq->lock);

  	work_clear_pending(work);

  	lock_map_acquire_read(&cwq->wq->lockdep_map);

  	lock_map_acquire(&lockdep_map);

  	trace_workqueue_execute_start(work);

  	f(work);

  	/*
  	 * While we must be careful to not use "work" after this, the trace
  	 * point will only record its address.
  	 */
  	trace_workqueue_execute_end(work);

  	lock_map_release(&lockdep_map);
  	lock_map_release(&cwq->wq->lockdep_map);
  
  	if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
  		printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
  		       "%s/0x%08x/%d
  ",
  		       current->comm, preempt_count(), task_pid_nr(current));
  		printk(KERN_ERR "    last function: ");
  		print_symbol("%s
  ", (unsigned long)f);
  		debug_show_held_locks(current);
  		dump_stack();
  	}

  	spin_lock_irq(&gcwq->lock);

  	/* clear cpu intensive status */
  	if (unlikely(cpu_intensive))
  		worker_clr_flags(worker, WORKER_CPU_INTENSIVE);

  	/* we're done with it, release */

  	hlist_del_init(&worker->hentry);

  	worker->current_work = NULL;

  	worker->current_cwq = NULL;

  	cwq_dec_nr_in_flight(cwq, work_color, false);

  }

  /**
   * process_scheduled_works - process scheduled works
   * @worker: self
   *
   * Process all scheduled works.  Please note that the scheduled list
   * may change while processing a work, so this function repeatedly
   * fetches a work from the top and executes it.
   *
   * CONTEXT:

   * spin_lock_irq(gcwq->lock) which may be released and regrabbed

   * multiple times.
   */
  static void process_scheduled_works(struct worker *worker)

  {

  	while (!list_empty(&worker->scheduled)) {
  		struct work_struct *work = list_first_entry(&worker->scheduled,

  						struct work_struct, entry);

  		process_one_work(worker, work);

  	}

  }

  /**
   * worker_thread - the worker thread function

   * @__worker: self

   *

   * The gcwq worker thread function.  There's a single dynamic pool of
   * these per each cpu.  These workers process all works regardless of
   * their specific target workqueue.  The only exception is works which
   * belong to workqueues with a rescuer which will be explained in
   * rescuer_thread().

   */

  static int worker_thread(void *__worker)

  {

  	struct worker *worker = __worker;

  	struct global_cwq *gcwq = worker->gcwq;

  	/* tell the scheduler that this is a workqueue worker */
  	worker->task->flags |= PF_WQ_WORKER;

  woke_up:

  	spin_lock_irq(&gcwq->lock);

  	/* DIE can be set only while we're idle, checking here is enough */
  	if (worker->flags & WORKER_DIE) {
  		spin_unlock_irq(&gcwq->lock);

  		worker->task->flags &= ~PF_WQ_WORKER;

  		return 0;
  	}

  	worker_leave_idle(worker);

  recheck:

  	/* no more worker necessary? */
  	if (!need_more_worker(gcwq))
  		goto sleep;
  
  	/* do we need to manage? */
  	if (unlikely(!may_start_working(gcwq)) && manage_workers(worker))
  		goto recheck;

  	/*
  	 * ->scheduled list can only be filled while a worker is
  	 * preparing to process a work or actually processing it.
  	 * Make sure nobody diddled with it while I was sleeping.
  	 */
  	BUG_ON(!list_empty(&worker->scheduled));

  	/*
  	 * When control reaches this point, we're guaranteed to have
  	 * at least one idle worker or that someone else has already
  	 * assumed the manager role.
  	 */
  	worker_clr_flags(worker, WORKER_PREP);
  
  	do {

  		struct work_struct *work =

  			list_first_entry(&gcwq->worklist,

  					 struct work_struct, entry);
  
  		if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
  			/* optimization path, not strictly necessary */
  			process_one_work(worker, work);
  			if (unlikely(!list_empty(&worker->scheduled)))

  				process_scheduled_works(worker);

  		} else {
  			move_linked_works(work, &worker->scheduled, NULL);
  			process_scheduled_works(worker);

  		}

  	} while (keep_working(gcwq));
  
  	worker_set_flags(worker, WORKER_PREP, false);

  sleep:

  	if (unlikely(need_to_manage_workers(gcwq)) && manage_workers(worker))
  		goto recheck;

  	/*

  	 * gcwq->lock is held and there's no work to process and no
  	 * need to manage, sleep.  Workers are woken up only while
  	 * holding gcwq->lock or from local cpu, so setting the
  	 * current state before releasing gcwq->lock is enough to
  	 * prevent losing any event.

  	 */
  	worker_enter_idle(worker);
  	__set_current_state(TASK_INTERRUPTIBLE);
  	spin_unlock_irq(&gcwq->lock);
  	schedule();
  	goto woke_up;

  }

  /**
   * rescuer_thread - the rescuer thread function
   * @__wq: the associated workqueue
   *
   * Workqueue rescuer thread function.  There's one rescuer for each
   * workqueue which has WQ_RESCUER set.
   *
   * Regular work processing on a gcwq may block trying to create a new
   * worker which uses GFP_KERNEL allocation which has slight chance of
   * developing into deadlock if some works currently on the same queue
   * need to be processed to satisfy the GFP_KERNEL allocation.  This is
   * the problem rescuer solves.
   *
   * When such condition is possible, the gcwq summons rescuers of all
   * workqueues which have works queued on the gcwq and let them process
   * those works so that forward progress can be guaranteed.
   *
   * This should happen rarely.
   */
  static int rescuer_thread(void *__wq)
  {
  	struct workqueue_struct *wq = __wq;
  	struct worker *rescuer = wq->rescuer;
  	struct list_head *scheduled = &rescuer->scheduled;

  	bool is_unbound = wq->flags & WQ_UNBOUND;

  	unsigned int cpu;
  
  	set_user_nice(current, RESCUER_NICE_LEVEL);
  repeat:
  	set_current_state(TASK_INTERRUPTIBLE);
  
  	if (kthread_should_stop())
  		return 0;

  	/*
  	 * See whether any cpu is asking for help.  Unbounded
  	 * workqueues use cpu 0 in mayday_mask for CPU_UNBOUND.
  	 */

  	for_each_mayday_cpu(cpu, wq->mayday_mask) {

  		unsigned int tcpu = is_unbound ? WORK_CPU_UNBOUND : cpu;
  		struct cpu_workqueue_struct *cwq = get_cwq(tcpu, wq);

  		struct global_cwq *gcwq = cwq->gcwq;
  		struct work_struct *work, *n;
  
  		__set_current_state(TASK_RUNNING);

  		mayday_clear_cpu(cpu, wq->mayday_mask);

  
  		/* migrate to the target cpu if possible */
  		rescuer->gcwq = gcwq;
  		worker_maybe_bind_and_lock(rescuer);
  
  		/*
  		 * Slurp in all works issued via this workqueue and
  		 * process'em.
  		 */
  		BUG_ON(!list_empty(&rescuer->scheduled));
  		list_for_each_entry_safe(work, n, &gcwq->worklist, entry)
  			if (get_work_cwq(work) == cwq)
  				move_linked_works(work, scheduled, &n);
  
  		process_scheduled_works(rescuer);

  
  		/*
  		 * Leave this gcwq.  If keep_working() is %true, notify a
  		 * regular worker; otherwise, we end up with 0 concurrency
  		 * and stalling the execution.
  		 */
  		if (keep_working(gcwq))
  			wake_up_worker(gcwq);

  		spin_unlock_irq(&gcwq->lock);
  	}
  
  	schedule();
  	goto repeat;

  }

  struct wq_barrier {
  	struct work_struct	work;
  	struct completion	done;
  };
  
  static void wq_barrier_func(struct work_struct *work)
  {
  	struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
  	complete(&barr->done);
  }

  /**
   * insert_wq_barrier - insert a barrier work
   * @cwq: cwq to insert barrier into
   * @barr: wq_barrier to insert

   * @target: target work to attach @barr to
   * @worker: worker currently executing @target, NULL if @target is not executing

   *

   * @barr is linked to @target such that @barr is completed only after
   * @target finishes execution.  Please note that the ordering
   * guarantee is observed only with respect to @target and on the local
   * cpu.
   *
   * Currently, a queued barrier can't be canceled.  This is because
   * try_to_grab_pending() can't determine whether the work to be
   * grabbed is at the head of the queue and thus can't clear LINKED
   * flag of the previous work while there must be a valid next work
   * after a work with LINKED flag set.
   *
   * Note that when @worker is non-NULL, @target may be modified
   * underneath us, so we can't reliably determine cwq from @target.

   *
   * CONTEXT:

   * spin_lock_irq(gcwq->lock).

   */

  static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,

  			      struct wq_barrier *barr,
  			      struct work_struct *target, struct worker *worker)

  {

  	struct list_head *head;
  	unsigned int linked = 0;

  	/*

  	 * debugobject calls are safe here even with gcwq->lock locked

  	 * as we know for sure that this will not trigger any of the
  	 * checks and call back into the fixup functions where we
  	 * might deadlock.
  	 */

  	INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);

  	__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));

  	init_completion(&barr->done);

  	/*
  	 * If @target is currently being executed, schedule the
  	 * barrier to the worker; otherwise, put it after @target.
  	 */
  	if (worker)
  		head = worker->scheduled.next;
  	else {
  		unsigned long *bits = work_data_bits(target);
  
  		head = target->entry.next;
  		/* there can already be other linked works, inherit and set */
  		linked = *bits & WORK_STRUCT_LINKED;
  		__set_bit(WORK_STRUCT_LINKED_BIT, bits);
  	}

  	debug_work_activate(&barr->work);

  	insert_work(cwq, &barr->work, head,
  		    work_color_to_flags(WORK_NO_COLOR) | linked);

  }

  /**
   * flush_workqueue_prep_cwqs - prepare cwqs for workqueue flushing
   * @wq: workqueue being flushed
   * @flush_color: new flush color, < 0 for no-op
   * @work_color: new work color, < 0 for no-op
   *
   * Prepare cwqs for workqueue flushing.
   *
   * If @flush_color is non-negative, flush_color on all cwqs should be
   * -1.  If no cwq has in-flight commands at the specified color, all
   * cwq->flush_color's stay at -1 and %false is returned.  If any cwq
   * has in flight commands, its cwq->flush_color is set to
   * @flush_color, @wq->nr_cwqs_to_flush is updated accordingly, cwq
   * wakeup logic is armed and %true is returned.
   *
   * The caller should have initialized @wq->first_flusher prior to
   * calling this function with non-negative @flush_color.  If
   * @flush_color is negative, no flush color update is done and %false
   * is returned.
   *
   * If @work_color is non-negative, all cwqs should have the same
   * work_color which is previous to @work_color and all will be
   * advanced to @work_color.
   *
   * CONTEXT:
   * mutex_lock(wq->flush_mutex).
   *
   * RETURNS:
   * %true if @flush_color >= 0 and there's something to flush.  %false
   * otherwise.
   */
  static bool flush_workqueue_prep_cwqs(struct workqueue_struct *wq,
  				      int flush_color, int work_color)