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fs/fscache/object.c 25.3 KB
36c955902   David Howells   FS-Cache: Object ...
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  /* FS-Cache object state machine handler
   *
   * Copyright (C) 2007 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 License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   *
   * See Documentation/filesystems/caching/object.txt for a description of the
   * object state machine and the in-kernel representations.
   */
  
  #define FSCACHE_DEBUG_LEVEL COOKIE
  #include <linux/module.h>
  #include "internal.h"
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  const char *fscache_object_states[FSCACHE_OBJECT__NSTATES] = {
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  	[FSCACHE_OBJECT_INIT]		= "OBJECT_INIT",
  	[FSCACHE_OBJECT_LOOKING_UP]	= "OBJECT_LOOKING_UP",
  	[FSCACHE_OBJECT_CREATING]	= "OBJECT_CREATING",
  	[FSCACHE_OBJECT_AVAILABLE]	= "OBJECT_AVAILABLE",
  	[FSCACHE_OBJECT_ACTIVE]		= "OBJECT_ACTIVE",
  	[FSCACHE_OBJECT_UPDATING]	= "OBJECT_UPDATING",
  	[FSCACHE_OBJECT_DYING]		= "OBJECT_DYING",
  	[FSCACHE_OBJECT_LC_DYING]	= "OBJECT_LC_DYING",
  	[FSCACHE_OBJECT_ABORT_INIT]	= "OBJECT_ABORT_INIT",
  	[FSCACHE_OBJECT_RELEASING]	= "OBJECT_RELEASING",
  	[FSCACHE_OBJECT_RECYCLING]	= "OBJECT_RECYCLING",
  	[FSCACHE_OBJECT_WITHDRAWING]	= "OBJECT_WITHDRAWING",
  	[FSCACHE_OBJECT_DEAD]		= "OBJECT_DEAD",
  };
  EXPORT_SYMBOL(fscache_object_states);
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  const char fscache_object_states_short[FSCACHE_OBJECT__NSTATES][5] = {
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  	[FSCACHE_OBJECT_INIT]		= "INIT",
  	[FSCACHE_OBJECT_LOOKING_UP]	= "LOOK",
  	[FSCACHE_OBJECT_CREATING]	= "CRTN",
  	[FSCACHE_OBJECT_AVAILABLE]	= "AVBL",
  	[FSCACHE_OBJECT_ACTIVE]		= "ACTV",
  	[FSCACHE_OBJECT_UPDATING]	= "UPDT",
  	[FSCACHE_OBJECT_DYING]		= "DYNG",
  	[FSCACHE_OBJECT_LC_DYING]	= "LCDY",
  	[FSCACHE_OBJECT_ABORT_INIT]	= "ABTI",
  	[FSCACHE_OBJECT_RELEASING]	= "RELS",
  	[FSCACHE_OBJECT_RECYCLING]	= "RCYC",
  	[FSCACHE_OBJECT_WITHDRAWING]	= "WTHD",
  	[FSCACHE_OBJECT_DEAD]		= "DEAD",
  };
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  static int  fscache_get_object(struct fscache_object *);
  static void fscache_put_object(struct fscache_object *);
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  static void fscache_initialise_object(struct fscache_object *);
  static void fscache_lookup_object(struct fscache_object *);
  static void fscache_object_available(struct fscache_object *);
  static void fscache_release_object(struct fscache_object *);
  static void fscache_withdraw_object(struct fscache_object *);
  static void fscache_enqueue_dependents(struct fscache_object *);
  static void fscache_dequeue_object(struct fscache_object *);
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  /*
   * we need to notify the parent when an op completes that we had outstanding
   * upon it
   */
  static inline void fscache_done_parent_op(struct fscache_object *object)
  {
  	struct fscache_object *parent = object->parent;
  
  	_enter("OBJ%x {OBJ%x,%x}",
  	       object->debug_id, parent->debug_id, parent->n_ops);
  
  	spin_lock_nested(&parent->lock, 1);
  	parent->n_ops--;
  	parent->n_obj_ops--;
  	if (parent->n_ops == 0)
  		fscache_raise_event(parent, FSCACHE_OBJECT_EV_CLEARED);
  	spin_unlock(&parent->lock);
  }
  
  /*
   * process events that have been sent to an object's state machine
   * - initiates parent lookup
   * - does object lookup
   * - does object creation
   * - does object recycling and retirement
   * - does object withdrawal
   */
  static void fscache_object_state_machine(struct fscache_object *object)
  {
  	enum fscache_object_state new_state;
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  	struct fscache_cookie *cookie;
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  	ASSERT(object != NULL);
  
  	_enter("{OBJ%x,%s,%lx}",
  	       object->debug_id, fscache_object_states[object->state],
  	       object->events);
  
  	switch (object->state) {
  		/* wait for the parent object to become ready */
  	case FSCACHE_OBJECT_INIT:
  		object->event_mask =
  			ULONG_MAX & ~(1 << FSCACHE_OBJECT_EV_CLEARED);
  		fscache_initialise_object(object);
  		goto done;
  
  		/* look up the object metadata on disk */
  	case FSCACHE_OBJECT_LOOKING_UP:
  		fscache_lookup_object(object);
  		goto lookup_transit;
  
  		/* create the object metadata on disk */
  	case FSCACHE_OBJECT_CREATING:
  		fscache_lookup_object(object);
  		goto lookup_transit;
  
  		/* handle an object becoming available; start pending
  		 * operations and queue dependent operations for processing */
  	case FSCACHE_OBJECT_AVAILABLE:
  		fscache_object_available(object);
  		goto active_transit;
  
  		/* normal running state */
  	case FSCACHE_OBJECT_ACTIVE:
  		goto active_transit;
  
  		/* update the object metadata on disk */
  	case FSCACHE_OBJECT_UPDATING:
  		clear_bit(FSCACHE_OBJECT_EV_UPDATE, &object->events);
  		fscache_stat(&fscache_n_updates_run);
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  		fscache_stat(&fscache_n_cop_update_object);
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  		object->cache->ops->update_object(object);
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  		fscache_stat_d(&fscache_n_cop_update_object);
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  		goto active_transit;
  
  		/* handle an object dying during lookup or creation */
  	case FSCACHE_OBJECT_LC_DYING:
  		object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE);
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  		fscache_stat(&fscache_n_cop_lookup_complete);
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  		object->cache->ops->lookup_complete(object);
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  		fscache_stat_d(&fscache_n_cop_lookup_complete);
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  		spin_lock(&object->lock);
  		object->state = FSCACHE_OBJECT_DYING;
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  		cookie = object->cookie;
  		if (cookie) {
  			if (test_and_clear_bit(FSCACHE_COOKIE_LOOKING_UP,
  					       &cookie->flags))
  				wake_up_bit(&cookie->flags,
  					    FSCACHE_COOKIE_LOOKING_UP);
  			if (test_and_clear_bit(FSCACHE_COOKIE_CREATING,
  					       &cookie->flags))
  				wake_up_bit(&cookie->flags,
  					    FSCACHE_COOKIE_CREATING);
  		}
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  		spin_unlock(&object->lock);
  
  		fscache_done_parent_op(object);
  
  		/* wait for completion of all active operations on this object
  		 * and the death of all child objects of this object */
  	case FSCACHE_OBJECT_DYING:
  	dying:
  		clear_bit(FSCACHE_OBJECT_EV_CLEARED, &object->events);
  		spin_lock(&object->lock);
  		_debug("dying OBJ%x {%d,%d}",
  		       object->debug_id, object->n_ops, object->n_children);
  		if (object->n_ops == 0 && object->n_children == 0) {
  			object->event_mask &=
  				~(1 << FSCACHE_OBJECT_EV_CLEARED);
  			object->event_mask |=
  				(1 << FSCACHE_OBJECT_EV_WITHDRAW) |
  				(1 << FSCACHE_OBJECT_EV_RETIRE) |
  				(1 << FSCACHE_OBJECT_EV_RELEASE) |
  				(1 << FSCACHE_OBJECT_EV_ERROR);
  		} else {
  			object->event_mask &=
  				~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
  				  (1 << FSCACHE_OBJECT_EV_RETIRE) |
  				  (1 << FSCACHE_OBJECT_EV_RELEASE) |
  				  (1 << FSCACHE_OBJECT_EV_ERROR));
  			object->event_mask |=
  				1 << FSCACHE_OBJECT_EV_CLEARED;
  		}
  		spin_unlock(&object->lock);
  		fscache_enqueue_dependents(object);
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  		fscache_start_operations(object);
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  		goto terminal_transit;
  
  		/* handle an abort during initialisation */
  	case FSCACHE_OBJECT_ABORT_INIT:
  		_debug("handle abort init %lx", object->events);
  		object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE);
  
  		spin_lock(&object->lock);
  		fscache_dequeue_object(object);
  
  		object->state = FSCACHE_OBJECT_DYING;
  		if (test_and_clear_bit(FSCACHE_COOKIE_CREATING,
  				       &object->cookie->flags))
  			wake_up_bit(&object->cookie->flags,
  				    FSCACHE_COOKIE_CREATING);
  		spin_unlock(&object->lock);
  		goto dying;
  
  		/* handle the netfs releasing an object and possibly marking it
  		 * obsolete too */
  	case FSCACHE_OBJECT_RELEASING:
  	case FSCACHE_OBJECT_RECYCLING:
  		object->event_mask &=
  			~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
  			  (1 << FSCACHE_OBJECT_EV_RETIRE) |
  			  (1 << FSCACHE_OBJECT_EV_RELEASE) |
  			  (1 << FSCACHE_OBJECT_EV_ERROR));
  		fscache_release_object(object);
  		spin_lock(&object->lock);
  		object->state = FSCACHE_OBJECT_DEAD;
  		spin_unlock(&object->lock);
  		fscache_stat(&fscache_n_object_dead);
  		goto terminal_transit;
  
  		/* handle the parent cache of this object being withdrawn from
  		 * active service */
  	case FSCACHE_OBJECT_WITHDRAWING:
  		object->event_mask &=
  			~((1 << FSCACHE_OBJECT_EV_WITHDRAW) |
  			  (1 << FSCACHE_OBJECT_EV_RETIRE) |
  			  (1 << FSCACHE_OBJECT_EV_RELEASE) |
  			  (1 << FSCACHE_OBJECT_EV_ERROR));
  		fscache_withdraw_object(object);
  		spin_lock(&object->lock);
  		object->state = FSCACHE_OBJECT_DEAD;
  		spin_unlock(&object->lock);
  		fscache_stat(&fscache_n_object_dead);
  		goto terminal_transit;
  
  		/* complain about the object being woken up once it is
  		 * deceased */
  	case FSCACHE_OBJECT_DEAD:
  		printk(KERN_ERR "FS-Cache:"
  		       " Unexpected event in dead state %lx
  ",
  		       object->events & object->event_mask);
  		BUG();
  
  	default:
  		printk(KERN_ERR "FS-Cache: Unknown object state %u
  ",
  		       object->state);
  		BUG();
  	}
  
  	/* determine the transition from a lookup state */
  lookup_transit:
  	switch (fls(object->events & object->event_mask) - 1) {
  	case FSCACHE_OBJECT_EV_WITHDRAW:
  	case FSCACHE_OBJECT_EV_RETIRE:
  	case FSCACHE_OBJECT_EV_RELEASE:
  	case FSCACHE_OBJECT_EV_ERROR:
  		new_state = FSCACHE_OBJECT_LC_DYING;
  		goto change_state;
  	case FSCACHE_OBJECT_EV_REQUEUE:
  		goto done;
  	case -1:
  		goto done; /* sleep until event */
  	default:
  		goto unsupported_event;
  	}
  
  	/* determine the transition from an active state */
  active_transit:
  	switch (fls(object->events & object->event_mask) - 1) {
  	case FSCACHE_OBJECT_EV_WITHDRAW:
  	case FSCACHE_OBJECT_EV_RETIRE:
  	case FSCACHE_OBJECT_EV_RELEASE:
  	case FSCACHE_OBJECT_EV_ERROR:
  		new_state = FSCACHE_OBJECT_DYING;
  		goto change_state;
  	case FSCACHE_OBJECT_EV_UPDATE:
  		new_state = FSCACHE_OBJECT_UPDATING;
  		goto change_state;
  	case -1:
  		new_state = FSCACHE_OBJECT_ACTIVE;
  		goto change_state; /* sleep until event */
  	default:
  		goto unsupported_event;
  	}
  
  	/* determine the transition from a terminal state */
  terminal_transit:
  	switch (fls(object->events & object->event_mask) - 1) {
  	case FSCACHE_OBJECT_EV_WITHDRAW:
  		new_state = FSCACHE_OBJECT_WITHDRAWING;
  		goto change_state;
  	case FSCACHE_OBJECT_EV_RETIRE:
  		new_state = FSCACHE_OBJECT_RECYCLING;
  		goto change_state;
  	case FSCACHE_OBJECT_EV_RELEASE:
  		new_state = FSCACHE_OBJECT_RELEASING;
  		goto change_state;
  	case FSCACHE_OBJECT_EV_ERROR:
  		new_state = FSCACHE_OBJECT_WITHDRAWING;
  		goto change_state;
  	case FSCACHE_OBJECT_EV_CLEARED:
  		new_state = FSCACHE_OBJECT_DYING;
  		goto change_state;
  	case -1:
  		goto done; /* sleep until event */
  	default:
  		goto unsupported_event;
  	}
  
  change_state:
  	spin_lock(&object->lock);
  	object->state = new_state;
  	spin_unlock(&object->lock);
  
  done:
  	_leave(" [->%s]", fscache_object_states[object->state]);
  	return;
  
  unsupported_event:
  	printk(KERN_ERR "FS-Cache:"
  	       " Unsupported event %lx [mask %lx] in state %s
  ",
  	       object->events, object->event_mask,
  	       fscache_object_states[object->state]);
  	BUG();
  }
  
  /*
   * execute an object
   */
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  void fscache_object_work_func(struct work_struct *work)
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  {
  	struct fscache_object *object =
  		container_of(work, struct fscache_object, work);
  	unsigned long start;
  
  	_enter("{OBJ%x}", object->debug_id);
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  	start = jiffies;
  	fscache_object_state_machine(object);
  	fscache_hist(fscache_objs_histogram, start);
  	if (object->events & object->event_mask)
  		fscache_enqueue_object(object);
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  	clear_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
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  	fscache_put_object(object);
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  }
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  EXPORT_SYMBOL(fscache_object_work_func);
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  /*
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   * initialise an object
   * - check the specified object's parent to see if we can make use of it
   *   immediately to do a creation
   * - we may need to start the process of creating a parent and we need to wait
   *   for the parent's lookup and creation to complete if it's not there yet
   * - an object's cookie is pinned until we clear FSCACHE_COOKIE_CREATING on the
   *   leaf-most cookies of the object and all its children
   */
  static void fscache_initialise_object(struct fscache_object *object)
  {
  	struct fscache_object *parent;
  
  	_enter("");
  	ASSERT(object->cookie != NULL);
  	ASSERT(object->cookie->parent != NULL);
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  	if (object->events & ((1 << FSCACHE_OBJECT_EV_ERROR) |
  			      (1 << FSCACHE_OBJECT_EV_RELEASE) |
  			      (1 << FSCACHE_OBJECT_EV_RETIRE) |
  			      (1 << FSCACHE_OBJECT_EV_WITHDRAW))) {
  		_debug("abort init %lx", object->events);
  		spin_lock(&object->lock);
  		object->state = FSCACHE_OBJECT_ABORT_INIT;
  		spin_unlock(&object->lock);
  		return;
  	}
  
  	spin_lock(&object->cookie->lock);
  	spin_lock_nested(&object->cookie->parent->lock, 1);
  
  	parent = object->parent;
  	if (!parent) {
  		_debug("no parent");
  		set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
  	} else {
  		spin_lock(&object->lock);
  		spin_lock_nested(&parent->lock, 1);
  		_debug("parent %s", fscache_object_states[parent->state]);
  
  		if (parent->state >= FSCACHE_OBJECT_DYING) {
  			_debug("bad parent");
  			set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
  		} else if (parent->state < FSCACHE_OBJECT_AVAILABLE) {
  			_debug("wait");
  
  			/* we may get woken up in this state by child objects
  			 * binding on to us, so we need to make sure we don't
  			 * add ourself to the list multiple times */
  			if (list_empty(&object->dep_link)) {
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  				fscache_stat(&fscache_n_cop_grab_object);
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  				object->cache->ops->grab_object(object);
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  				fscache_stat_d(&fscache_n_cop_grab_object);
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  				list_add(&object->dep_link,
  					 &parent->dependents);
  
  				/* fscache_acquire_non_index_cookie() uses this
  				 * to wake the chain up */
  				if (parent->state == FSCACHE_OBJECT_INIT)
  					fscache_enqueue_object(parent);
  			}
  		} else {
  			_debug("go");
  			parent->n_ops++;
  			parent->n_obj_ops++;
  			object->lookup_jif = jiffies;
  			object->state = FSCACHE_OBJECT_LOOKING_UP;
  			set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
  		}
  
  		spin_unlock(&parent->lock);
  		spin_unlock(&object->lock);
  	}
  
  	spin_unlock(&object->cookie->parent->lock);
  	spin_unlock(&object->cookie->lock);
  	_leave("");
  }
  
  /*
   * look an object up in the cache from which it was allocated
   * - we hold an "access lock" on the parent object, so the parent object cannot
   *   be withdrawn by either party till we've finished
   * - an object's cookie is pinned until we clear FSCACHE_COOKIE_CREATING on the
   *   leaf-most cookies of the object and all its children
   */
  static void fscache_lookup_object(struct fscache_object *object)
  {
  	struct fscache_cookie *cookie = object->cookie;
  	struct fscache_object *parent;
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  	int ret;
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  	_enter("");
  
  	parent = object->parent;
  	ASSERT(parent != NULL);
  	ASSERTCMP(parent->n_ops, >, 0);
  	ASSERTCMP(parent->n_obj_ops, >, 0);
  
  	/* make sure the parent is still available */
  	ASSERTCMP(parent->state, >=, FSCACHE_OBJECT_AVAILABLE);
  
  	if (parent->state >= FSCACHE_OBJECT_DYING ||
  	    test_bit(FSCACHE_IOERROR, &object->cache->flags)) {
  		_debug("unavailable");
  		set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
  		_leave("");
  		return;
  	}
  
  	_debug("LOOKUP \"%s/%s\" in \"%s\"",
  	       parent->cookie->def->name, cookie->def->name,
  	       object->cache->tag->name);
  
  	fscache_stat(&fscache_n_object_lookups);
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  	fscache_stat(&fscache_n_cop_lookup_object);
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  	ret = object->cache->ops->lookup_object(object);
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  	fscache_stat_d(&fscache_n_cop_lookup_object);
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  	if (test_bit(FSCACHE_OBJECT_EV_ERROR, &object->events))
  		set_bit(FSCACHE_COOKIE_UNAVAILABLE, &cookie->flags);
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  	if (ret == -ETIMEDOUT) {
  		/* probably stuck behind another object, so move this one to
  		 * the back of the queue */
  		fscache_stat(&fscache_n_object_lookups_timed_out);
  		set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
  	}
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  	_leave("");
  }
  
  /**
   * fscache_object_lookup_negative - Note negative cookie lookup
   * @object: Object pointing to cookie to mark
   *
   * Note negative lookup, permitting those waiting to read data from an already
   * existing backing object to continue as there's no data for them to read.
   */
  void fscache_object_lookup_negative(struct fscache_object *object)
  {
  	struct fscache_cookie *cookie = object->cookie;
  
  	_enter("{OBJ%x,%s}",
  	       object->debug_id, fscache_object_states[object->state]);
  
  	spin_lock(&object->lock);
  	if (object->state == FSCACHE_OBJECT_LOOKING_UP) {
  		fscache_stat(&fscache_n_object_lookups_negative);
  
  		/* transit here to allow write requests to begin stacking up
  		 * and read requests to begin returning ENODATA */
  		object->state = FSCACHE_OBJECT_CREATING;
  		spin_unlock(&object->lock);
  
  		set_bit(FSCACHE_COOKIE_PENDING_FILL, &cookie->flags);
  		set_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
  
  		_debug("wake up lookup %p", &cookie->flags);
  		smp_mb__before_clear_bit();
  		clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);
  		smp_mb__after_clear_bit();
  		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
  		set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
  	} else {
  		ASSERTCMP(object->state, ==, FSCACHE_OBJECT_CREATING);
  		spin_unlock(&object->lock);
  	}
  
  	_leave("");
  }
  EXPORT_SYMBOL(fscache_object_lookup_negative);
  
  /**
   * fscache_obtained_object - Note successful object lookup or creation
   * @object: Object pointing to cookie to mark
   *
   * Note successful lookup and/or creation, permitting those waiting to write
   * data to a backing object to continue.
   *
   * Note that after calling this, an object's cookie may be relinquished by the
   * netfs, and so must be accessed with object lock held.
   */
  void fscache_obtained_object(struct fscache_object *object)
  {
  	struct fscache_cookie *cookie = object->cookie;
  
  	_enter("{OBJ%x,%s}",
  	       object->debug_id, fscache_object_states[object->state]);
  
  	/* if we were still looking up, then we must have a positive lookup
  	 * result, in which case there may be data available */
  	spin_lock(&object->lock);
  	if (object->state == FSCACHE_OBJECT_LOOKING_UP) {
  		fscache_stat(&fscache_n_object_lookups_positive);
  
  		clear_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
  
  		object->state = FSCACHE_OBJECT_AVAILABLE;
  		spin_unlock(&object->lock);
  
  		smp_mb__before_clear_bit();
  		clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);
  		smp_mb__after_clear_bit();
  		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
  		set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
  	} else {
  		ASSERTCMP(object->state, ==, FSCACHE_OBJECT_CREATING);
  		fscache_stat(&fscache_n_object_created);
  
  		object->state = FSCACHE_OBJECT_AVAILABLE;
  		spin_unlock(&object->lock);
  		set_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
  		smp_wmb();
  	}
  
  	if (test_and_clear_bit(FSCACHE_COOKIE_CREATING, &cookie->flags))
  		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_CREATING);
  
  	_leave("");
  }
  EXPORT_SYMBOL(fscache_obtained_object);
  
  /*
   * handle an object that has just become available
   */
  static void fscache_object_available(struct fscache_object *object)
  {
  	_enter("{OBJ%x}", object->debug_id);
  
  	spin_lock(&object->lock);
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  	if (object->cookie &&
  	    test_and_clear_bit(FSCACHE_COOKIE_CREATING, &object->cookie->flags))
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  		wake_up_bit(&object->cookie->flags, FSCACHE_COOKIE_CREATING);
  
  	fscache_done_parent_op(object);
  	if (object->n_in_progress == 0) {
  		if (object->n_ops > 0) {
  			ASSERTCMP(object->n_ops, >=, object->n_obj_ops);
  			ASSERTIF(object->n_ops > object->n_obj_ops,
  				 !list_empty(&object->pending_ops));
  			fscache_start_operations(object);
  		} else {
  			ASSERT(list_empty(&object->pending_ops));
  		}
  	}
  	spin_unlock(&object->lock);
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  	fscache_stat(&fscache_n_cop_lookup_complete);
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  	object->cache->ops->lookup_complete(object);
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  	fscache_stat_d(&fscache_n_cop_lookup_complete);
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  	fscache_enqueue_dependents(object);
  
  	fscache_hist(fscache_obj_instantiate_histogram, object->lookup_jif);
  	fscache_stat(&fscache_n_object_avail);
  
  	_leave("");
  }
  
  /*
   * drop an object's attachments
   */
  static void fscache_drop_object(struct fscache_object *object)
  {
  	struct fscache_object *parent = object->parent;
  	struct fscache_cache *cache = object->cache;
  
  	_enter("{OBJ%x,%d}", object->debug_id, object->n_children);
6897e3df8   David Howells   FS-Cache: The obj...
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  	ASSERTCMP(object->cookie, ==, NULL);
  	ASSERT(hlist_unhashed(&object->cookie_link));
36c955902   David Howells   FS-Cache: Object ...
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  	spin_lock(&cache->object_list_lock);
  	list_del_init(&object->cache_link);
  	spin_unlock(&cache->object_list_lock);
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  	fscache_stat(&fscache_n_cop_drop_object);
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  	cache->ops->drop_object(object);
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  	fscache_stat_d(&fscache_n_cop_drop_object);
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  	if (parent) {
  		_debug("release parent OBJ%x {%d}",
  		       parent->debug_id, parent->n_children);
  
  		spin_lock(&parent->lock);
  		parent->n_children--;
  		if (parent->n_children == 0)
  			fscache_raise_event(parent, FSCACHE_OBJECT_EV_CLEARED);
  		spin_unlock(&parent->lock);
  		object->parent = NULL;
  	}
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  	/* this just shifts the object release to the work processor */
  	fscache_put_object(object);
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  	_leave("");
  }
  
  /*
   * release or recycle an object that the netfs has discarded
   */
  static void fscache_release_object(struct fscache_object *object)
  {
  	_enter("");
  
  	fscache_drop_object(object);
  }
  
  /*
   * withdraw an object from active service
   */
  static void fscache_withdraw_object(struct fscache_object *object)
  {
  	struct fscache_cookie *cookie;
  	bool detached;
  
  	_enter("");
  
  	spin_lock(&object->lock);
  	cookie = object->cookie;
  	if (cookie) {
  		/* need to get the cookie lock before the object lock, starting
  		 * from the object pointer */
  		atomic_inc(&cookie->usage);
  		spin_unlock(&object->lock);
  
  		detached = false;
  		spin_lock(&cookie->lock);
  		spin_lock(&object->lock);
  
  		if (object->cookie == cookie) {
  			hlist_del_init(&object->cookie_link);
  			object->cookie = NULL;
  			detached = true;
  		}
  		spin_unlock(&cookie->lock);
  		fscache_cookie_put(cookie);
  		if (detached)
  			fscache_cookie_put(cookie);
  	}
  
  	spin_unlock(&object->lock);
  
  	fscache_drop_object(object);
  }
  
  /*
   * withdraw an object from active service at the behest of the cache
   * - need break the links to a cached object cookie
   * - called under two situations:
   *   (1) recycler decides to reclaim an in-use object
   *   (2) a cache is unmounted
   * - have to take care as the cookie can be being relinquished by the netfs
   *   simultaneously
   * - the object is pinned by the caller holding a refcount on it
   */
  void fscache_withdrawing_object(struct fscache_cache *cache,
  				struct fscache_object *object)
  {
  	bool enqueue = false;
  
  	_enter(",OBJ%x", object->debug_id);
  
  	spin_lock(&object->lock);
  	if (object->state < FSCACHE_OBJECT_WITHDRAWING) {
  		object->state = FSCACHE_OBJECT_WITHDRAWING;
  		enqueue = true;
  	}
  	spin_unlock(&object->lock);
  
  	if (enqueue)
  		fscache_enqueue_object(object);
  
  	_leave("");
  }
  
  /*
8b8edefa2   Tejun Heo   fscache: convert ...
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   * get a ref on an object
36c955902   David Howells   FS-Cache: Object ...
719
   */
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  static int fscache_get_object(struct fscache_object *object)
36c955902   David Howells   FS-Cache: Object ...
721
  {
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  	int ret;
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723

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  	fscache_stat(&fscache_n_cop_grab_object);
  	ret = object->cache->ops->grab_object(object) ? 0 : -EAGAIN;
  	fscache_stat_d(&fscache_n_cop_grab_object);
  	return ret;
36c955902   David Howells   FS-Cache: Object ...
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  }
  
  /*
8b8edefa2   Tejun Heo   fscache: convert ...
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   * discard a ref on a work item
36c955902   David Howells   FS-Cache: Object ...
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   */
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733
  static void fscache_put_object(struct fscache_object *object)
36c955902   David Howells   FS-Cache: Object ...
734
  {
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  	fscache_stat(&fscache_n_cop_put_object);
  	object->cache->ops->put_object(object);
  	fscache_stat_d(&fscache_n_cop_put_object);
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  }
  
  /*
   * enqueue an object for metadata-type processing
   */
  void fscache_enqueue_object(struct fscache_object *object)
  {
  	_enter("{OBJ%x}", object->debug_id);
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  	if (fscache_get_object(object) >= 0) {
  		wait_queue_head_t *cong_wq =
  			&get_cpu_var(fscache_object_cong_wait);
  
  		if (queue_work(fscache_object_wq, &object->work)) {
  			if (fscache_object_congested())
  				wake_up(cong_wq);
  		} else
  			fscache_put_object(object);
  
  		put_cpu_var(fscache_object_cong_wait);
  	}
  }
  
  /**
   * fscache_object_sleep_till_congested - Sleep until object wq is congested
   * @timoutp: Scheduler sleep timeout
   *
   * Allow an object handler to sleep until the object workqueue is congested.
   *
   * 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.
   *
   * %true is returned if the object wq is congested, %false otherwise.
   */
  bool fscache_object_sleep_till_congested(signed long *timeoutp)
  {
  	wait_queue_head_t *cong_wq = &__get_cpu_var(fscache_object_cong_wait);
  	DEFINE_WAIT(wait);
  
  	if (fscache_object_congested())
  		return true;
  
  	add_wait_queue_exclusive(cong_wq, &wait);
  	if (!fscache_object_congested())
  		*timeoutp = schedule_timeout(*timeoutp);
  	finish_wait(cong_wq, &wait);
  
  	return fscache_object_congested();
36c955902   David Howells   FS-Cache: Object ...
786
  }
8b8edefa2   Tejun Heo   fscache: convert ...
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  EXPORT_SYMBOL_GPL(fscache_object_sleep_till_congested);
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  /*
   * enqueue the dependents of an object for metadata-type processing
   * - the caller must hold the object's lock
   * - this may cause an already locked object to wind up being processed again
   */
  static void fscache_enqueue_dependents(struct fscache_object *object)
  {
  	struct fscache_object *dep;
  
  	_enter("{OBJ%x}", object->debug_id);
  
  	if (list_empty(&object->dependents))
  		return;
  
  	spin_lock(&object->lock);
  
  	while (!list_empty(&object->dependents)) {
  		dep = list_entry(object->dependents.next,
  				 struct fscache_object, dep_link);
  		list_del_init(&dep->dep_link);
  
  
  		/* sort onto appropriate lists */
  		fscache_enqueue_object(dep);
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  		fscache_put_object(dep);
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  		if (!list_empty(&object->dependents))
  			cond_resched_lock(&object->lock);
  	}
  
  	spin_unlock(&object->lock);
  }
  
  /*
   * remove an object from whatever queue it's waiting on
   * - the caller must hold object->lock
   */
  void fscache_dequeue_object(struct fscache_object *object)
  {
  	_enter("{OBJ%x}", object->debug_id);
  
  	if (!list_empty(&object->dep_link)) {
  		spin_lock(&object->parent->lock);
  		list_del_init(&object->dep_link);
  		spin_unlock(&object->parent->lock);
  	}
  
  	_leave("");
  }
  
  /**
   * fscache_check_aux - Ask the netfs whether an object on disk is still valid
   * @object: The object to ask about
   * @data: The auxiliary data for the object
   * @datalen: The size of the auxiliary data
   *
   * This function consults the netfs about the coherency state of an object
   */
  enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
  					const void *data, uint16_t datalen)
  {
  	enum fscache_checkaux result;
  
  	if (!object->cookie->def->check_aux) {
  		fscache_stat(&fscache_n_checkaux_none);
  		return FSCACHE_CHECKAUX_OKAY;
  	}
  
  	result = object->cookie->def->check_aux(object->cookie->netfs_data,
  						data, datalen);
  	switch (result) {
  		/* entry okay as is */
  	case FSCACHE_CHECKAUX_OKAY:
  		fscache_stat(&fscache_n_checkaux_okay);
  		break;
  
  		/* entry requires update */
  	case FSCACHE_CHECKAUX_NEEDS_UPDATE:
  		fscache_stat(&fscache_n_checkaux_update);
  		break;
  
  		/* entry requires deletion */
  	case FSCACHE_CHECKAUX_OBSOLETE:
  		fscache_stat(&fscache_n_checkaux_obsolete);
  		break;
  
  	default:
  		BUG();
  	}
  
  	return result;
  }
  EXPORT_SYMBOL(fscache_check_aux);