FS-Cache: Fix object state machine to have separate work and wait states

Fix object state machine to have separate work and wait states as that makes
it easier to envision.

There are now three kinds of state:

(1) Work state. This is an execution state. No event processing is performed
by a work state. The function attached to a work state returns a pointer
indicating the next state to which the OSM should transition. Returning
NO_TRANSIT repeats the current state, but goes back to the scheduler
first.

(2) Wait state. This is an event processing state. No execution is
performed by a wait state. Wait states are just tables of "if event X
occurs, clear it and transition to state Y". The dispatcher returns to
the scheduler if none of the events in which the wait state has an
interest are currently pending.

(3) Out-of-band state. This is a special work state. Transitions to normal
states can be overridden when an unexpected event occurs (eg. I/O error).
Instead the dispatcher disables and clears the OOB event and transits to
the specified work state. This then acts as an ordinary work state,
though object->state points to the overridden destination. Returning
NO_TRANSIT resumes the overridden transition.

In addition, the states have names in their definitions, so there's no need for
tables of state names. Further, the EV_REQUEUE event is no longer necessary as
that is automatic for work states.

Since the states are now separate structs rather than values in an enum, it's
not possible to use comparisons other than (non-)equality between them, so use
some object->flags to indicate what phase an object is in.

The EV_RELEASE, EV_RETIRE and EV_WITHDRAW events have been squished into one
(EV_KILL). An object flag now carries the information about retirement.

Similarly, the RELEASING, RECYCLING and WITHDRAWING states have been merged
into an KILL_OBJECT state and additional states have been added for handling
waiting dependent objects (JUMPSTART_DEPS and KILL_DEPENDENTS).

A state has also been added for synchronising with parent object initialisation
(WAIT_FOR_PARENT) and another for initiating look up (PARENT_READY).

Signed-off-by: David Howells <[e-mail]>
Tested-By: Milosz Tanski <[e-mail]>
Acked-by: Jeff Layton <[e-mail]>

fs/cachefiles/interface.c

···
 #endif
 
 	/* delete retired objects */
-	if (object->fscache.state == FSCACHE_OBJECT_RECYCLING &&
+	if (test_bit(FSCACHE_OBJECT_RETIRE, &object->fscache.flags) &&
 	    _object != cache->cache.fsdef
 	    ) {
 		_debug("- retire object OBJ%x", object->fscache.debug_id);

fs/cachefiles/namei.c

···
 	printk(KERN_ERR "%sobject: OBJ%x\n",
 	       prefix, object->fscache.debug_id);
 	printk(KERN_ERR "%sobjstate=%s fl=%lx wbusy=%x ev=%lx[%lx]\n",
-	       prefix, fscache_object_states[object->fscache.state],
+	       prefix, object->fscache.state->name,
 	       object->fscache.flags, work_busy(&object->fscache.work),
 	       object->fscache.events, object->fscache.event_mask);
 	printk(KERN_ERR "%sops=%u inp=%u exc=%u\n",
···
 found_dentry:
 	kdebug("preemptive burial: OBJ%x [%s] %p",
 	       object->fscache.debug_id,
-	       fscache_object_states[object->fscache.state],
+	       object->fscache.state->name,
 	       dentry);
 
 	if (fscache_object_is_live(&object->fscache)) {

fs/fscache/cache.c

···
 	BUG_ON(!ifsdef);
 
 	cache->flags = 0;
-	ifsdef->event_mask = ULONG_MAX & ~(1 << FSCACHE_OBJECT_EV_CLEARED);
-	ifsdef->state = FSCACHE_OBJECT_ACTIVE;
+	ifsdef->event_mask =
+		((1 << NR_FSCACHE_OBJECT_EVENTS) - 1) &
+		~(1 << FSCACHE_OBJECT_EV_CLEARED);
+	__set_bit(FSCACHE_OBJECT_IS_AVAILABLE, &ifsdef->flags);
 
 	if (!tagname)
 		tagname = cache->identifier;
···
 {
 	struct fscache_object *object;
 
-	spin_lock(&cache->object_list_lock);
-
 	while (!list_empty(&cache->object_list)) {
-		object = list_entry(cache->object_list.next,
-				    struct fscache_object, cache_link);
-		list_move_tail(&object->cache_link, dying_objects);
-
-		_debug("withdraw %p", object->cookie);
-
-		spin_lock(&object->lock);
-		spin_unlock(&cache->object_list_lock);
-		fscache_raise_event(object, FSCACHE_OBJECT_EV_WITHDRAW);
-		spin_unlock(&object->lock);
-
-		cond_resched();
 		spin_lock(&cache->object_list_lock);
-	}
 
-	spin_unlock(&cache->object_list_lock);
+		if (!list_empty(&cache->object_list)) {
+			object = list_entry(cache->object_list.next,
+					    struct fscache_object, cache_link);
+			list_move_tail(&object->cache_link, dying_objects);
+
+			_debug("withdraw %p", object->cookie);
+
+			/* This must be done under object_list_lock to prevent
+			 * a race with fscache_drop_object().
+			 */
+			fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
+		}
+
+		spin_unlock(&cache->object_list_lock);
+		cond_resched();
+	}
 }
 
 /**

fs/fscache/cookie.c

···
 
 	/* initiate the process of looking up all the objects in the chain
 	 * (done by fscache_initialise_object()) */
-	fscache_enqueue_object(object);
+	fscache_raise_event(object, FSCACHE_OBJECT_EV_NEW_CHILD);
 
 	spin_unlock(&cookie->lock);
 
···
 {
 	struct fscache_cache *cache;
 	struct fscache_object *object;
-	unsigned long event;
 
 	fscache_stat(&fscache_n_relinquishes);
 	if (retire)
···
 		wait_on_bit(&cookie->flags, FSCACHE_COOKIE_CREATING,
 			    fscache_wait_bit, TASK_UNINTERRUPTIBLE);
 	}
-
-	event = retire ? FSCACHE_OBJECT_EV_RETIRE : FSCACHE_OBJECT_EV_RELEASE;
 
 try_again:
 	spin_lock(&cookie->lock);
···
 
 		cache = object->cache;
 		object->cookie = NULL;
-		fscache_raise_event(object, event);
+		if (retire)
+			set_bit(FSCACHE_OBJECT_RETIRE, &object->flags);
+		fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
 		spin_unlock(&object->lock);
 
 		if (atomic_dec_and_test(&cookie->usage))

fs/fscache/internal.h

···
 /*
  * object.c
  */
-extern const char fscache_object_states_short[FSCACHE_OBJECT__NSTATES][5];
-
-extern void fscache_withdrawing_object(struct fscache_cache *,
-				       struct fscache_object *);
 extern void fscache_enqueue_object(struct fscache_object *);
 
 /*
···
 				       unsigned event)
 {
 	BUG_ON(event >= NR_FSCACHE_OBJECT_EVENTS);
+#if 0
+	printk("*** fscache_raise_event(OBJ%d{%lx},%x)\n",
+	       object->debug_id, object->event_mask, (1 << event));
+#endif
 	if (!test_and_set_bit(event, &object->events) &&
 	    test_bit(event, &object->event_mask))
 		fscache_enqueue_object(object);

fs/fscache/object-list.c

···
 
 	if ((unsigned long) v == 1) {
 		seq_puts(m, "OBJECT   PARENT   STAT CHLDN OPS OOP IPR EX READS"
-			 " EM EV F S"
+			 " EM EV FL S"
 			 " | NETFS_COOKIE_DEF TY FL NETFS_DATA");
 		if (config & (FSCACHE_OBJLIST_CONFIG_KEY |
 			      FSCACHE_OBJLIST_CONFIG_AUX))
···
 
 	if ((unsigned long) v == 2) {
 		seq_puts(m, "======== ======== ==== ===== === === === == ====="
-			 " == == = ="
+			 " == == == ="
 			 " | ================ == == ================");
 		if (config & (FSCACHE_OBJLIST_CONFIG_KEY |
 			      FSCACHE_OBJLIST_CONFIG_AUX))
···
 	if (~config) {
 		FILTER(obj->cookie,
 		       COOKIE, NOCOOKIE);
-		FILTER(obj->state != FSCACHE_OBJECT_ACTIVE ||
+		FILTER(fscache_object_is_active(obj) ||
 		       obj->n_ops != 0 ||
 		       obj->n_obj_ops != 0 ||
 		       obj->flags ||
···
 	}
 
 	seq_printf(m,
-		   "%8x %8x %s %5u %3u %3u %3u %2u %5u %2lx %2lx %1lx %1x | ",
+		   "%8x %8x %s %5u %3u %3u %3u %2u %5u %2lx %2lx %2lx %1x | ",
 		   obj->debug_id,
 		   obj->parent ? obj->parent->debug_id : -1,
-		   fscache_object_states_short[obj->state],
+		   obj->state->short_name,
 		   obj->n_children,
 		   obj->n_ops,
 		   obj->n_obj_ops,

fs/fscache/object.c

···
 #define FSCACHE_DEBUG_LEVEL COOKIE
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <linux/prefetch.h>
 #include "internal.h"
 
-const char *fscache_object_states[FSCACHE_OBJECT__NSTATES] = {
-	[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_INVALIDATING]	= "OBJECT_INVALIDATING",
-	[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);
+static const struct fscache_state *fscache_abort_initialisation(struct fscache_object *, int);
+static const struct fscache_state *fscache_kill_dependents(struct fscache_object *, int);
+static const struct fscache_state *fscache_drop_object(struct fscache_object *, int);
+static const struct fscache_state *fscache_initialise_object(struct fscache_object *, int);
+static const struct fscache_state *fscache_invalidate_object(struct fscache_object *, int);
+static const struct fscache_state *fscache_jumpstart_dependents(struct fscache_object *, int);
+static const struct fscache_state *fscache_kill_object(struct fscache_object *, int);
+static const struct fscache_state *fscache_lookup_failure(struct fscache_object *, int);
+static const struct fscache_state *fscache_look_up_object(struct fscache_object *, int);
+static const struct fscache_state *fscache_object_available(struct fscache_object *, int);
+static const struct fscache_state *fscache_parent_ready(struct fscache_object *, int);
+static const struct fscache_state *fscache_update_object(struct fscache_object *, int);
+static const struct fscache_state *fscache_detach_from_cookie(struct fscache_object *, int);
 
-const char fscache_object_states_short[FSCACHE_OBJECT__NSTATES][5] = {
-	[FSCACHE_OBJECT_INIT]		= "INIT",
-	[FSCACHE_OBJECT_LOOKING_UP]	= "LOOK",
-	[FSCACHE_OBJECT_CREATING]	= "CRTN",
-	[FSCACHE_OBJECT_AVAILABLE]	= "AVBL",
-	[FSCACHE_OBJECT_ACTIVE]		= "ACTV",
-	[FSCACHE_OBJECT_INVALIDATING]	= "INVL",
-	[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",
+#define __STATE_NAME(n) fscache_osm_##n
+#define STATE(n) (&__STATE_NAME(n))
+
+/*
+ * Define a work state.  Work states are execution states.  No event processing
+ * is performed by them.  The function attached to a work state returns a
+ * pointer indicating the next state to which the state machine should
+ * transition.  Returning NO_TRANSIT repeats the current state, but goes back
+ * to the scheduler first.
+ */
+#define WORK_STATE(n, sn, f) \
+	const struct fscache_state __STATE_NAME(n) = {			\
+		.name = #n,						\
+		.short_name = sn,					\
+		.work = f						\
+	}
+
+/*
+ * Returns from work states.
+ */
+#define transit_to(state) ({ prefetch(&STATE(state)->work); STATE(state); })
+
+#define NO_TRANSIT ((struct fscache_state *)NULL)
+
+/*
+ * Define a wait state.  Wait states are event processing states.  No execution
+ * is performed by them.  Wait states are just tables of "if event X occurs,
+ * clear it and transition to state Y".  The dispatcher returns to the
+ * scheduler if none of the events in which the wait state has an interest are
+ * currently pending.
+ */
+#define WAIT_STATE(n, sn, ...) \
+	const struct fscache_state __STATE_NAME(n) = {			\
+		.name = #n,						\
+		.short_name = sn,					\
+		.work = NULL,						\
+		.transitions = { __VA_ARGS__, { 0, NULL } }		\
+	}
+
+#define TRANSIT_TO(state, emask) \
+	{ .events = (emask), .transit_to = STATE(state) }
+
+/*
+ * The object state machine.
+ */
+static WORK_STATE(INIT_OBJECT,		"INIT", fscache_initialise_object);
+static WORK_STATE(PARENT_READY,		"PRDY", fscache_parent_ready);
+static WORK_STATE(ABORT_INIT,		"ABRT", fscache_abort_initialisation);
+static WORK_STATE(LOOK_UP_OBJECT,	"LOOK", fscache_look_up_object);
+static WORK_STATE(CREATE_OBJECT,	"CRTO", fscache_look_up_object);
+static WORK_STATE(OBJECT_AVAILABLE,	"AVBL", fscache_object_available);
+static WORK_STATE(JUMPSTART_DEPS,	"JUMP", fscache_jumpstart_dependents);
+
+static WORK_STATE(INVALIDATE_OBJECT,	"INVL", fscache_invalidate_object);
+static WORK_STATE(UPDATE_OBJECT,	"UPDT", fscache_update_object);
+
+static WORK_STATE(LOOKUP_FAILURE,	"LCFL", fscache_lookup_failure);
+static WORK_STATE(KILL_OBJECT,		"KILL", fscache_kill_object);
+static WORK_STATE(KILL_DEPENDENTS,	"KDEP", fscache_kill_dependents);
+static WORK_STATE(DROP_OBJECT,		"DROP", fscache_drop_object);
+static WORK_STATE(DETACH_FROM_COOKIE,	"DTCH", fscache_detach_from_cookie);
+static WORK_STATE(OBJECT_DEAD,		"DEAD", (void*)2UL);
+
+static WAIT_STATE(WAIT_FOR_INIT,	"?INI",
+		  TRANSIT_TO(INIT_OBJECT,	1 << FSCACHE_OBJECT_EV_NEW_CHILD));
+
+static WAIT_STATE(WAIT_FOR_PARENT,	"?PRN",
+		  TRANSIT_TO(PARENT_READY,	1 << FSCACHE_OBJECT_EV_PARENT_READY));
+
+static WAIT_STATE(WAIT_FOR_CMD,		"?CMD",
+		  TRANSIT_TO(INVALIDATE_OBJECT,	1 << FSCACHE_OBJECT_EV_INVALIDATE),
+		  TRANSIT_TO(UPDATE_OBJECT,	1 << FSCACHE_OBJECT_EV_UPDATE),
+		  TRANSIT_TO(JUMPSTART_DEPS,	1 << FSCACHE_OBJECT_EV_NEW_CHILD));
+
+static WAIT_STATE(WAIT_FOR_CLEARANCE,	"?CLR",
+		  TRANSIT_TO(KILL_OBJECT,	1 << FSCACHE_OBJECT_EV_CLEARED));
+
+/*
+ * Out-of-band event transition tables.  These are for handling unexpected
+ * events, such as an I/O error.  If an OOB event occurs, the state machine
+ * clears and disables the event and forces a transition to the nominated work
+ * state (acurrently executing work states will complete first).
+ *
+ * In such a situation, object->state remembers the state the machine should
+ * have been in/gone to and returning NO_TRANSIT returns to that.
+ */
+static const struct fscache_transition fscache_osm_init_oob[] = {
+	   TRANSIT_TO(ABORT_INIT,
+		      (1 << FSCACHE_OBJECT_EV_ERROR) |
+		      (1 << FSCACHE_OBJECT_EV_KILL)),
+	   { 0, NULL }
+};
+
+static const struct fscache_transition fscache_osm_lookup_oob[] = {
+	   TRANSIT_TO(LOOKUP_FAILURE,
+		      (1 << FSCACHE_OBJECT_EV_ERROR) |
+		      (1 << FSCACHE_OBJECT_EV_KILL)),
+	   { 0, NULL }
+};
+
+static const struct fscache_transition fscache_osm_run_oob[] = {
+	   TRANSIT_TO(KILL_OBJECT,
+		      (1 << FSCACHE_OBJECT_EV_ERROR) |
+		      (1 << FSCACHE_OBJECT_EV_KILL)),
+	   { 0, NULL }
 };
 
 static int  fscache_get_object(struct fscache_object *);
 static void fscache_put_object(struct fscache_object *);
-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_invalidate_object(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 bool fscache_enqueue_dependents(struct fscache_object *, int);
 static void fscache_dequeue_object(struct fscache_object *);
 
 /*
···
 }
 
 /*
- * Notify netfs of invalidation completion.
+ * Object state machine dispatcher.
  */
-static inline void fscache_invalidation_complete(struct fscache_cookie *cookie)
+static void fscache_object_sm_dispatcher(struct fscache_object *object)
 {
-	if (test_and_clear_bit(FSCACHE_COOKIE_INVALIDATING, &cookie->flags))
-		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_INVALIDATING);
-}
-
-/*
- * 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;
-	struct fscache_cookie *cookie;
-	int event;
+	const struct fscache_transition *t;
+	const struct fscache_state *state, *new_state;
+	unsigned long events, event_mask;
+	int event = -1;
 
 	ASSERT(object != NULL);
 
 	_enter("{OBJ%x,%s,%lx}",
-	       object->debug_id, fscache_object_states[object->state],
-	       object->events);
+	       object->debug_id, object->state->name, object->events);
 
-	switch (object->state) {
-		/* wait for the parent object to become ready */
-	case FSCACHE_OBJECT_INIT:
-		object->event_mask =
-			FSCACHE_OBJECT_EVENTS_MASK &
-			~(1 << FSCACHE_OBJECT_EV_CLEARED);
-		fscache_initialise_object(object);
-		goto done;
+	event_mask = object->event_mask;
+restart:
+	object->event_mask = 0; /* Mask normal event handling */
+	state = object->state;
+restart_masked:
+	events = object->events;
 
-		/* 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;
-
-		/* Invalidate an object on disk */
-	case FSCACHE_OBJECT_INVALIDATING:
-		clear_bit(FSCACHE_OBJECT_EV_INVALIDATE, &object->events);
-		fscache_stat(&fscache_n_invalidates_run);
-		fscache_stat(&fscache_n_cop_invalidate_object);
-		fscache_invalidate_object(object);
-		fscache_stat_d(&fscache_n_cop_invalidate_object);
-		fscache_raise_event(object, FSCACHE_OBJECT_EV_UPDATE);
-		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);
-		fscache_stat(&fscache_n_cop_update_object);
-		object->cache->ops->update_object(object);
-		fscache_stat_d(&fscache_n_cop_update_object);
-		goto active_transit;
-
-		/* handle an object dying during lookup or creation */
-	case FSCACHE_OBJECT_LC_DYING:
-		object->event_mask &= ~(1 << FSCACHE_OBJECT_EV_UPDATE);
-		fscache_stat(&fscache_n_cop_lookup_complete);
-		object->cache->ops->lookup_complete(object);
-		fscache_stat_d(&fscache_n_cop_lookup_complete);
-
-		spin_lock(&object->lock);
-		object->state = FSCACHE_OBJECT_DYING;
-		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);
+	/* Handle any out-of-band events (typically an error) */
+	if (events & object->oob_event_mask) {
+		_debug("{OBJ%x} oob %lx",
+		       object->debug_id, events & object->oob_event_mask);
+		for (t = object->oob_table; t->events; t++) {
+			if (events & t->events) {
+				state = t->transit_to;
+				ASSERT(state->work != NULL);
+				event = fls(events & t->events) - 1;
+				__clear_bit(event, &object->oob_event_mask);
+				clear_bit(event, &object->events);
+				goto execute_work_state;
+			}
 		}
-		spin_unlock(&object->lock);
+	}
 
-		fscache_done_parent_op(object);
+	/* Wait states are just transition tables */
+	if (!state->work) {
+		if (events & event_mask) {
+			for (t = state->transitions; t->events; t++) {
+				if (events & t->events) {
+					new_state = t->transit_to;
+					event = fls(events & t->events) - 1;
+					clear_bit(event, &object->events);
+					_debug("{OBJ%x} ev %d: %s -> %s",
+					       object->debug_id, event,
+					       state->name, new_state->name);
+					object->state = state = new_state;
+					goto execute_work_state;
+				}
+			}
 
-		/* 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;
+			/* The event mask didn't include all the tabled bits */
+			BUG();
 		}
-		spin_unlock(&object->lock);
-		fscache_enqueue_dependents(object);
-		fscache_start_operations(object);
-		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\n",
-		       object->events & object->event_mask);
-		BUG();
-
-	default:
-		printk(KERN_ERR "FS-Cache: Unknown object state %u\n",
-		       object->state);
-		BUG();
+		/* Randomly woke up */
+		goto unmask_events;
 	}
 
-	/* determine the transition from a lookup state */
-lookup_transit:
-	event = fls(object->events & object->event_mask) - 1;
-	switch (event) {
-	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_INVALIDATE:
-		new_state = FSCACHE_OBJECT_INVALIDATING;
-		goto change_state;
-	case FSCACHE_OBJECT_EV_REQUEUE:
-		goto done;
-	case -1:
-		goto done; /* sleep until event */
-	default:
-		goto unsupported_event;
+execute_work_state:
+	_debug("{OBJ%x} exec %s", object->debug_id, state->name);
+
+	new_state = state->work(object, event);
+	event = -1;
+	if (new_state == NO_TRANSIT) {
+		_debug("{OBJ%x} %s notrans", object->debug_id, state->name);
+		fscache_enqueue_object(object);
+		event_mask = object->oob_event_mask;
+		goto unmask_events;
 	}
 
-	/* determine the transition from an active state */
-active_transit:
-	event = fls(object->events & object->event_mask) - 1;
-	switch (event) {
-	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_INVALIDATE:
-		new_state = FSCACHE_OBJECT_INVALIDATING;
-		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;
+	_debug("{OBJ%x} %s -> %s",
+	       object->debug_id, state->name, new_state->name);
+	object->state = state = new_state;
+
+	if (state->work) {
+		if (unlikely(state->work == ((void *)2UL))) {
+			_leave(" [dead]");
+			return;
+		}
+		goto restart_masked;
 	}
 
-	/* determine the transition from a terminal state */
-terminal_transit:
-	event = fls(object->events & object->event_mask) - 1;
-	switch (event) {
-	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;
-	}
+	/* Transited to wait state */
+	event_mask = object->oob_event_mask;
+	for (t = state->transitions; t->events; t++)
+		event_mask |= t->events;
 
-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 %d [%lx/%lx] in state %s\n",
-	       event, object->events, object->event_mask,
-	       fscache_object_states[object->state]);
-	BUG();
+unmask_events:
+	object->event_mask = event_mask;
+	smp_mb();
+	events = object->events;
+	if (events & event_mask)
+		goto restart;
+	_leave(" [msk %lx]", event_mask);
 }
 
 /*
···
 	_enter("{OBJ%x}", object->debug_id);
 
 	start = jiffies;
-	fscache_object_state_machine(object);
+	fscache_object_sm_dispatcher(object);
 	fscache_hist(fscache_objs_histogram, start);
-	if (object->events & object->event_mask)
-		fscache_enqueue_object(object);
-	clear_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
 	fscache_put_object(object);
 }
 
···
 			 struct fscache_cookie *cookie,
 			 struct fscache_cache *cache)
 {
+	const struct fscache_transition *t;
+
 	atomic_inc(&cache->object_count);
 
-	object->state = FSCACHE_OBJECT_INIT;
+	object->state = STATE(WAIT_FOR_INIT);
+	object->oob_table = fscache_osm_init_oob;
+	object->flags = 1 << FSCACHE_OBJECT_IS_LIVE;
 	spin_lock_init(&object->lock);
 	INIT_LIST_HEAD(&object->cache_link);
 	INIT_HLIST_NODE(&object->cookie_link);
···
 	INIT_LIST_HEAD(&object->pending_ops);
 	object->n_children = 0;
 	object->n_ops = object->n_in_progress = object->n_exclusive = 0;
-	object->events = object->event_mask = 0;
-	object->flags = 0;
+	object->events = 0;
 	object->store_limit = 0;
 	object->store_limit_l = 0;
 	object->cache = cache;
 	object->cookie = cookie;
 	object->parent = NULL;
+
+	object->oob_event_mask = 0;
+	for (t = object->oob_table; t->events; t++)
+		object->oob_event_mask |= t->events;
+	object->event_mask = object->oob_event_mask;
+	for (t = object->state->transitions; t->events; t++)
+		object->event_mask |= t->events;
 }
 EXPORT_SYMBOL(fscache_object_init);
+
+/*
+ * Abort object initialisation before we start it.
+ */
+static const struct fscache_state *fscache_abort_initialisation(struct fscache_object *object,
+								int event)
+{
+	struct fscache_cookie *cookie;
+
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
+	object->oob_event_mask = 0;
+	clear_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
+
+	fscache_dequeue_object(object);
+
+	spin_lock(&object->lock);
+	cookie = object->cookie;
+	clear_bit_unlock(FSCACHE_COOKIE_CREATING, &cookie->flags);
+	spin_unlock(&object->lock);
+
+	wake_up_bit(&cookie->flags, FSCACHE_COOKIE_CREATING);
+
+	return transit_to(KILL_OBJECT);
+}
 
 /*
  * initialise an object
···
  * - 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)
+static const struct fscache_state *fscache_initialise_object(struct fscache_object *object,
+							     int event)
 {
 	struct fscache_object *parent;
+	bool success;
 
-	_enter("");
-	ASSERT(object->cookie != NULL);
-	ASSERT(object->cookie->parent != NULL);
+	_enter("{OBJ%x},%d", object->debug_id, event);
 
-	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);
+	ASSERT(list_empty(&object->dep_link));
 
 	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 (fscache_object_is_dying(parent)) {
-			_debug("bad parent");
-			set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
-		} else if (!fscache_object_is_available(parent)) {
-			_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)) {
-				fscache_stat(&fscache_n_cop_grab_object);
-				object->cache->ops->grab_object(object);
-				fscache_stat_d(&fscache_n_cop_grab_object);
-				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);
+		_leave(" [no parent]");
+		return transit_to(DETACH_FROM_COOKIE);
 	}
 
-	spin_unlock(&object->cookie->parent->lock);
-	spin_unlock(&object->cookie->lock);
+	_debug("parent %s", parent->state->name);
+
+	if (fscache_object_is_dying(parent)) {
+		_leave(" [bad parent]");
+		return transit_to(DETACH_FROM_COOKIE);
+	}
+
+	if (fscache_object_is_available(parent)) {
+		_leave(" [ready]");
+		return transit_to(PARENT_READY);
+	}
+
+	_debug("wait");
+
+	spin_lock(&parent->lock);
+	fscache_stat(&fscache_n_cop_grab_object);
+	success = false;
+	if (fscache_object_is_live(parent) &&
+	    object->cache->ops->grab_object(object)) {
+		list_add(&object->dep_link, &parent->dependents);
+		success = true;
+	}
+	fscache_stat_d(&fscache_n_cop_grab_object);
+	spin_unlock(&parent->lock);
+	if (!success) {
+		_leave(" [grab failed]");
+		return transit_to(DETACH_FROM_COOKIE);
+	}
+
+	/* fscache_acquire_non_index_cookie() uses this
+	 * to wake the chain up */
+	fscache_raise_event(parent, FSCACHE_OBJECT_EV_NEW_CHILD);
+	_leave(" [wait]");
+	return transit_to(WAIT_FOR_PARENT);
+}
+
+/*
+ * Once the parent object is ready, we should kick off our lookup op.
+ */
+static const struct fscache_state *fscache_parent_ready(struct fscache_object *object,
+							int event)
+{
+	struct fscache_object *parent = object->parent;
+
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
+	ASSERT(parent != NULL);
+
+	spin_lock(&parent->lock);
+	parent->n_ops++;
+	parent->n_obj_ops++;
+	object->lookup_jif = jiffies;
+	spin_unlock(&parent->lock);
+
 	_leave("");
+	return transit_to(LOOK_UP_OBJECT);
 }
 
 /*
···
  * - 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)
+static const struct fscache_state *fscache_look_up_object(struct fscache_object *object,
+							  int event)
 {
 	struct fscache_cookie *cookie = object->cookie;
-	struct fscache_object *parent;
+	struct fscache_object *parent = object->parent;
 	int ret;
 
-	_enter("");
+	_enter("{OBJ%x},%d", object->debug_id, event);
 
-	parent = object->parent;
+	object->oob_table = fscache_osm_lookup_oob;
+
 	ASSERT(parent != NULL);
 	ASSERTCMP(parent->n_ops, >, 0);
 	ASSERTCMP(parent->n_obj_ops, >, 0);
···
 
 	if (fscache_object_is_dying(parent) ||
 	    test_bit(FSCACHE_IOERROR, &object->cache->flags)) {
-		_debug("unavailable");
-		set_bit(FSCACHE_OBJECT_EV_WITHDRAW, &object->events);
-		_leave("");
-		return;
+		_leave(" [unavailable]");
+		return transit_to(LOOKUP_FAILURE);
 	}
 
 	_debug("LOOKUP \"%s/%s\" in \"%s\"",
···
 		/* 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);
+		_leave(" [timeout]");
+		return NO_TRANSIT;
 	}
 
-	_leave("");
+	if (ret < 0) {
+		_leave(" [error]");
+		return transit_to(LOOKUP_FAILURE);
+	}
+
+	_leave(" [ok]");
+	return transit_to(OBJECT_AVAILABLE);
 }
 
 /**
···
 {
 	struct fscache_cookie *cookie = object->cookie;
 
-	_enter("{OBJ%x,%s}",
-	       object->debug_id, fscache_object_states[object->state]);
+	_enter("{OBJ%x,%s}", object->debug_id, object->state->name);
 
-	spin_lock(&object->lock);
-	if (object->state == FSCACHE_OBJECT_LOOKING_UP) {
+	if (!test_and_set_bit(FSCACHE_OBJECT_IS_LOOKED_UP, &object->flags)) {
 		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);
+		/* Allow write requests to begin stacking up and read requests to begin
+		 * returning ENODATA.
+		 */
 		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();
+		clear_bit_unlock(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);
 		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);
···
 {
 	struct fscache_cookie *cookie = object->cookie;
 
-	_enter("{OBJ%x,%s}",
-	       object->debug_id, fscache_object_states[object->state]);
+	_enter("{OBJ%x,%s}", object->debug_id, object->state->name);
 
 	/* 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) {
+	if (!test_and_set_bit(FSCACHE_OBJECT_IS_LOOKED_UP, &object->flags)) {
 		fscache_stat(&fscache_n_object_lookups_positive);
 
-		clear_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
+		/* We do (presumably) have data */
+		clear_bit_unlock(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();
+		/* Allow write requests to begin stacking up and read requests
+		 * to begin shovelling data.
+		 */
+		clear_bit_unlock(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);
 		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);
+	set_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
+
+	/* Permit __fscache_relinquish_cookie() to proceed */
+	clear_bit_unlock(FSCACHE_COOKIE_CREATING, &cookie->flags);
+	wake_up_bit(&cookie->flags, FSCACHE_COOKIE_CREATING);
 
 	_leave("");
 }
···
 /*
  * handle an object that has just become available
  */
-static void fscache_object_available(struct fscache_object *object)
+static const struct fscache_state *fscache_object_available(struct fscache_object *object,
+							    int event)
 {
-	_enter("{OBJ%x}", object->debug_id);
+	struct fscache_cookie *cookie = object->cookie;
+
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
+	object->oob_table = fscache_osm_run_oob;
 
 	spin_lock(&object->lock);
 
-	if (object->cookie &&
-	    test_and_clear_bit(FSCACHE_COOKIE_CREATING, &object->cookie->flags))
-		wake_up_bit(&object->cookie->flags, FSCACHE_COOKIE_CREATING);
+	ASSERTIF(cookie, !test_bit(FSCACHE_COOKIE_CREATING, &object->cookie->flags));
 
 	fscache_done_parent_op(object);
 	if (object->n_in_progress == 0) {
···
 	fscache_stat(&fscache_n_cop_lookup_complete);
 	object->cache->ops->lookup_complete(object);
 	fscache_stat_d(&fscache_n_cop_lookup_complete);
-	fscache_enqueue_dependents(object);
 
 	fscache_hist(fscache_obj_instantiate_histogram, object->lookup_jif);
 	fscache_stat(&fscache_n_object_avail);
 
 	_leave("");
+	return transit_to(JUMPSTART_DEPS);
 }
 
 /*
- * drop an object's attachments
+ * Wake up this object's dependent objects now that we've become available.
  */
-static void fscache_drop_object(struct fscache_object *object)
+static const struct fscache_state *fscache_jumpstart_dependents(struct fscache_object *object,
+								int event)
+{
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
+	if (!fscache_enqueue_dependents(object, FSCACHE_OBJECT_EV_PARENT_READY))
+		return NO_TRANSIT; /* Not finished; requeue */
+	return transit_to(WAIT_FOR_CMD);
+}
+
+/*
+ * Handle lookup or creation failute.
+ */
+static const struct fscache_state *fscache_lookup_failure(struct fscache_object *object,
+							  int event)
+{
+	struct fscache_cookie *cookie;
+	bool wake_looking_up = false;
+
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
+	object->oob_event_mask = 0;
+
+	fscache_stat(&fscache_n_cop_lookup_complete);
+	object->cache->ops->lookup_complete(object);
+	fscache_stat_d(&fscache_n_cop_lookup_complete);
+
+	spin_lock(&object->lock);
+	cookie = object->cookie;
+	set_bit(FSCACHE_COOKIE_UNAVAILABLE, &cookie->flags);
+	if (cookie) {
+		if (test_and_clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags))
+			wake_looking_up = true;
+		clear_bit_unlock(FSCACHE_COOKIE_CREATING, &cookie->flags);
+	}
+	spin_unlock(&object->lock);
+
+	if (wake_looking_up)
+		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
+	wake_up_bit(&cookie->flags, FSCACHE_COOKIE_CREATING);
+
+	fscache_done_parent_op(object);
+	return transit_to(KILL_OBJECT);
+}
+
+/*
+ * Wait for completion of all active operations on this object and the death of
+ * all child objects of this object.
+ */
+static const struct fscache_state *fscache_kill_object(struct fscache_object *object,
+						       int event)
+{
+	_enter("{OBJ%x,%d,%d},%d",
+	       object->debug_id, object->n_ops, object->n_children, event);
+
+	object->oob_event_mask = 0;
+
+	spin_lock(&object->lock);
+	clear_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
+	spin_unlock(&object->lock);
+
+	if (list_empty(&object->dependents) &&
+	    object->n_ops == 0 &&
+	    object->n_children == 0)
+		return object->cookie ?
+			transit_to(DETACH_FROM_COOKIE) : transit_to(DROP_OBJECT);
+
+	spin_lock(&object->lock);
+	fscache_start_operations(object);
+	spin_unlock(&object->lock);
+
+	if (!list_empty(&object->dependents))
+		return transit_to(KILL_DEPENDENTS);
+
+	return transit_to(WAIT_FOR_CLEARANCE);
+}
+
+/*
+ * Kill dependent objects.
+ */
+static const struct fscache_state *fscache_kill_dependents(struct fscache_object *object,
+							   int event)
+{
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
+	if (!fscache_enqueue_dependents(object, FSCACHE_OBJECT_EV_KILL))
+		return NO_TRANSIT; /* Not finished */
+	return transit_to(WAIT_FOR_CLEARANCE);
+}
+
+/*
+ * withdraw an object from active service
+ */
+static const struct fscache_state *fscache_detach_from_cookie(struct fscache_object *object,
+							      int event)
+{
+	struct fscache_cookie *cookie;
+	bool detached = false, awaken = false;
+
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
+	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);
+
+		spin_lock(&cookie->lock);
+		spin_lock(&object->lock);
+
+		if (object->cookie == cookie) {
+			hlist_del_init(&object->cookie_link);
+			object->cookie = NULL;
+			if (test_and_clear_bit(FSCACHE_COOKIE_INVALIDATING,
+					       &cookie->flags))
+				awaken = true;
+			detached = true;
+		}
+		spin_unlock(&cookie->lock);
+		fscache_cookie_put(cookie);
+		if (detached)
+			fscache_cookie_put(cookie);
+	}
+
+	spin_unlock(&object->lock);
+
+	if (awaken)
+		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_INVALIDATING);
+
+	fscache_stat(&fscache_n_object_dead);
+	_leave("");
+	return transit_to(DROP_OBJECT);
+}
+
+/*
+ * Drop an object's attachments
+ */
+static const struct fscache_state *fscache_drop_object(struct fscache_object *object,
+						       int event)
 {
 	struct fscache_object *parent = object->parent;
 	struct fscache_cache *cache = object->cache;
 
-	_enter("{OBJ%x,%d}", object->debug_id, object->n_children);
+	_enter("{OBJ%x,%d},%d", object->debug_id, object->n_children, event);
 
 	ASSERTCMP(object->cookie, ==, NULL);
 	ASSERT(hlist_unhashed(&object->cookie_link));
 
+	/* Prevent a race with our last child, which has to signal EV_CLEARED
+	 * before dropping our spinlock.
+	 */
+	spin_lock(&object->lock);
+	spin_unlock(&object->lock);
+
+	/* Discard from the cache's collection of objects */
 	spin_lock(&cache->object_list_lock);
 	list_del_init(&object->cache_link);
 	spin_unlock(&cache->object_list_lock);
···
 	cache->ops->drop_object(object);
 	fscache_stat_d(&fscache_n_cop_drop_object);
 
+	/* The parent object wants to know when all it dependents have gone */
 	if (parent) {
 		_debug("release parent OBJ%x {%d}",
 		       parent->debug_id, parent->n_children);
···
 
 	/* this just shifts the object release to the work processor */
 	fscache_put_object(object);
+	fscache_stat(&fscache_n_object_dead);
 
 	_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;
-			fscache_invalidation_complete(cookie);
-			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("");
+	return transit_to(OBJECT_DEAD);
 }
 
 /*
···
 }
 
 /*
- * discard a ref on a work item
+ * Discard a ref on an object
  */
 static void fscache_put_object(struct fscache_object *object)
 {
···
 
 /**
  * fscache_object_sleep_till_congested - Sleep until object wq is congested
- * @timoutp: Scheduler sleep timeout
+ * @timeoutp: Scheduler sleep timeout
  *
  * Allow an object handler to sleep until the object workqueue is congested.
  *
···
 EXPORT_SYMBOL_GPL(fscache_object_sleep_till_congested);
 
 /*
- * 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
+ * Enqueue the dependents of an object for metadata-type processing.
+ *
+ * If we don't manage to finish the list before the scheduler wants to run
+ * again then return false immediately.  We return true if the list was
+ * cleared.
  */
-static void fscache_enqueue_dependents(struct fscache_object *object)
+static bool fscache_enqueue_dependents(struct fscache_object *object, int event)
 {
 	struct fscache_object *dep;
+	bool ret = true;
 
 	_enter("{OBJ%x}", object->debug_id);
 
 	if (list_empty(&object->dependents))
-		return;
+		return true;
 
 	spin_lock(&object->lock);
 
···
 				 struct fscache_object, dep_link);
 		list_del_init(&dep->dep_link);
 
-
-		/* sort onto appropriate lists */
-		fscache_enqueue_object(dep);
+		fscache_raise_event(dep, event);
 		fscache_put_object(dep);
 
-		if (!list_empty(&object->dependents))
-			cond_resched_lock(&object->lock);
+		if (!list_empty(&object->dependents) && need_resched()) {
+			ret = false;
+			break;
+		}
 	}
 
 	spin_unlock(&object->lock);
+	return ret;
 }
 
 /*
  * remove an object from whatever queue it's waiting on
- * - the caller must hold object->lock
  */
-void fscache_dequeue_object(struct fscache_object *object)
+static void fscache_dequeue_object(struct fscache_object *object)
 {
 	_enter("{OBJ%x}", object->debug_id);
 
···
 /*
  * Asynchronously invalidate an object.
  */
-static void fscache_invalidate_object(struct fscache_object *object)
+static const struct fscache_state *_fscache_invalidate_object(struct fscache_object *object,
+							      int event)
 {
 	struct fscache_operation *op;
 	struct fscache_cookie *cookie = object->cookie;
 
-	_enter("{OBJ%x}", object->debug_id);
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
 
 	/* Reject any new read/write ops and abort any that are pending. */
 	fscache_invalidate_writes(cookie);
···
 	/* Now we have to wait for in-progress reads and writes */
 	op = kzalloc(sizeof(*op), GFP_KERNEL);
 	if (!op) {
-		fscache_raise_event(object, FSCACHE_OBJECT_EV_ERROR);
+		clear_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
 		_leave(" [ENOMEM]");
-		return;
+		return transit_to(KILL_OBJECT);
 	}
 
 	fscache_operation_init(op, object->cache->ops->invalidate_object, NULL);
···
 	/* We can allow read and write requests to come in once again.  They'll
 	 * queue up behind our exclusive invalidation operation.
 	 */
-	fscache_invalidation_complete(cookie);
-	_leave("");
-	return;
+	if (test_and_clear_bit(FSCACHE_COOKIE_INVALIDATING, &cookie->flags))
+		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_INVALIDATING);
+	_leave(" [ok]");
+	return transit_to(UPDATE_OBJECT);
 
 submit_op_failed:
+	clear_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
 	spin_unlock(&cookie->lock);
 	kfree(op);
-	fscache_raise_event(object, FSCACHE_OBJECT_EV_ERROR);
 	_leave(" [EIO]");
+	return transit_to(KILL_OBJECT);
+}
+
+static const struct fscache_state *fscache_invalidate_object(struct fscache_object *object,
+							     int event)
+{
+	const struct fscache_state *s;
+
+	fscache_stat(&fscache_n_invalidates_run);
+	fscache_stat(&fscache_n_cop_invalidate_object);
+	s = _fscache_invalidate_object(object, event);
+	fscache_stat_d(&fscache_n_cop_invalidate_object);
+	return s;
+}
+
+/*
+ * Asynchronously update an object.
+ */
+static const struct fscache_state *fscache_update_object(struct fscache_object *object,
+							 int event)
+{
+	_enter("{OBJ%x},%d", object->debug_id, event);
+
+	fscache_stat(&fscache_n_updates_run);
+	fscache_stat(&fscache_n_cop_update_object);
+	object->cache->ops->update_object(object);
+	fscache_stat_d(&fscache_n_cop_update_object);
+
+	_leave("");
+	return transit_to(WAIT_FOR_CMD);
 }

fs/fscache/operation.c

···
 		/* need to issue a new write op after this */
 		clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
 		ret = 0;
-	} else if (object->state == FSCACHE_OBJECT_CREATING) {
+	} else if (test_bit(FSCACHE_OBJECT_IS_LOOKED_UP, &object->flags)) {
 		op->object = object;
 		object->n_ops++;
 		object->n_exclusive++;	/* reads and writes must wait */
···
  */
 static void fscache_report_unexpected_submission(struct fscache_object *object,
 						 struct fscache_operation *op,
-						 unsigned long ostate)
+						 const struct fscache_state *ostate)
 {
 	static bool once_only;
 	struct fscache_operation *p;
···
 	once_only = true;
 
 	kdebug("unexpected submission OP%x [OBJ%x %s]",
-	       op->debug_id, object->debug_id,
-	       fscache_object_states[object->state]);
-	kdebug("objstate=%s [%s]",
-	       fscache_object_states[object->state],
-	       fscache_object_states[ostate]);
+	       op->debug_id, object->debug_id, object->state->name);
+	kdebug("objstate=%s [%s]", object->state->name, ostate->name);
 	kdebug("objflags=%lx", object->flags);
 	kdebug("objevent=%lx [%lx]", object->events, object->event_mask);
 	kdebug("ops=%u inp=%u exc=%u",
···
 int fscache_submit_op(struct fscache_object *object,
 		      struct fscache_operation *op)
 {
-	unsigned long ostate;
+	const struct fscache_state *ostate;
 	int ret;
 
 	_enter("{OBJ%x OP%x},{%u}",
···
 			fscache_run_op(object, op);
 		}
 		ret = 0;
-	} else if (object->state == FSCACHE_OBJECT_CREATING) {
+	} else if (test_bit(FSCACHE_OBJECT_IS_LOOKED_UP, &object->flags)) {
 		op->object = object;
 		object->n_ops++;
 		atomic_inc(&op->usage);
 		list_add_tail(&op->pend_link, &object->pending_ops);
 		fscache_stat(&fscache_n_op_pend);
 		ret = 0;
-	} else if (object->state == FSCACHE_OBJECT_DYING ||
-		   object->state == FSCACHE_OBJECT_LC_DYING ||
-		   object->state == FSCACHE_OBJECT_WITHDRAWING) {
+	} else if (fscache_object_is_dying(object)) {
 		fscache_stat(&fscache_n_op_rejected);
 		op->state = FSCACHE_OP_ST_CANCELLED;
 		ret = -ENOBUFS;
···
 
 /*
  * jump start the operation processing on an object
- * - caller must hold object->lock
  */
 void fscache_start_operations(struct fscache_object *object)
 {
 	struct fscache_operation *op;
 	bool stop = false;
+
+	ASSERT(spin_is_locked(&object->lock));
 
 	while (!list_empty(&object->pending_ops) && !stop) {
 		op = list_entry(object->pending_ops.next,

fs/fscache/page.c

···
 	object = hlist_entry(cookie->backing_objects.first,
 			     struct fscache_object, cookie_link);
 
-	ASSERTCMP(object->state, >, FSCACHE_OBJECT_LOOKING_UP);
+	ASSERT(test_bit(FSCACHE_OBJECT_IS_LOOKED_UP, &object->flags));
 
 	atomic_inc(&object->n_reads);
 	__set_bit(FSCACHE_OP_DEC_READ_CNT, &op->op.flags);
···
 		 */
 		spin_unlock(&object->lock);
 		fscache_op_complete(&op->op, false);
-		_leave(" [cancel] op{f=%lx s=%u} obj{s=%u f=%lx}",
-		       _op->flags, _op->state, object->state, object->flags);
+		_leave(" [cancel] op{f=%lx s=%u} obj{s=%s f=%lx}",
+		       _op->flags, _op->state, object->state->short_name,
+		       object->flags);
 		return;
 	}
 
···
  *  (1) negative lookup, object not yet created (FSCACHE_COOKIE_CREATING is
  *      set)
  *
- *	(a) no writes yet (set FSCACHE_COOKIE_PENDING_FILL and queue deferred
- *	    fill op)
+ *	(a) no writes yet
  *
  *	(b) writes deferred till post-creation (mark page for writing and
  *	    return immediately)
  *
  *  (2) negative lookup, object created, initial fill being made from netfs
- *      (FSCACHE_COOKIE_INITIAL_FILL is set)
  *
  *	(a) fill point not yet reached this page (mark page for writing and
  *          return)

include/linux/fscache-cache.h

···
 #define FSCACHE_COOKIE_LOOKING_UP	0	/* T if non-index cookie being looked up still */
 #define FSCACHE_COOKIE_CREATING		1	/* T if non-index object being created still */
 #define FSCACHE_COOKIE_NO_DATA_YET	2	/* T if new object with no cached data yet */
-#define FSCACHE_COOKIE_PENDING_FILL	3	/* T if pending initial fill on object */
-#define FSCACHE_COOKIE_FILLING		4	/* T if filling object incrementally */
-#define FSCACHE_COOKIE_UNAVAILABLE	5	/* T if cookie is unavailable (error, etc) */
-#define FSCACHE_COOKIE_WAITING_ON_READS	6	/* T if cookie is waiting on reads */
-#define FSCACHE_COOKIE_INVALIDATING	7	/* T if cookie is being invalidated */
+#define FSCACHE_COOKIE_UNAVAILABLE	3	/* T if cookie is unavailable (error, etc) */
+#define FSCACHE_COOKIE_WAITING_ON_READS	4	/* T if cookie is waiting on reads */
+#define FSCACHE_COOKIE_INVALIDATING	5	/* T if cookie is being invalidated */
 };
 
 extern struct fscache_cookie fscache_fsdef_index;
···
  * Event list for fscache_object::{event_mask,events}
  */
 enum {
-	FSCACHE_OBJECT_EV_REQUEUE,	/* T if object should be requeued */
+	FSCACHE_OBJECT_EV_NEW_CHILD,	/* T if object has a new child */
+	FSCACHE_OBJECT_EV_PARENT_READY,	/* T if object's parent is ready */
 	FSCACHE_OBJECT_EV_UPDATE,	/* T if object should be updated */
 	FSCACHE_OBJECT_EV_INVALIDATE,	/* T if cache requested object invalidation */
 	FSCACHE_OBJECT_EV_CLEARED,	/* T if accessors all gone */
 	FSCACHE_OBJECT_EV_ERROR,	/* T if fatal error occurred during processing */
-	FSCACHE_OBJECT_EV_RELEASE,	/* T if netfs requested object release */
-	FSCACHE_OBJECT_EV_RETIRE,	/* T if netfs requested object retirement */
-	FSCACHE_OBJECT_EV_WITHDRAW,	/* T if cache requested object withdrawal */
+	FSCACHE_OBJECT_EV_KILL,		/* T if netfs relinquished or cache withdrew object */
 	NR_FSCACHE_OBJECT_EVENTS
 };
 
 #define FSCACHE_OBJECT_EVENTS_MASK ((1UL << NR_FSCACHE_OBJECT_EVENTS) - 1)
 
 /*
+ * States for object state machine.
+ */
+struct fscache_transition {
+	unsigned long events;
+	const struct fscache_state *transit_to;
+};
+
+struct fscache_state {
+	char name[24];
+	char short_name[8];
+	const struct fscache_state *(*work)(struct fscache_object *object,
+					    int event);
+	const struct fscache_transition transitions[];
+};
+
+/*
  * on-disk cache file or index handle
  */
 struct fscache_object {
-	enum fscache_object_state {
-		FSCACHE_OBJECT_INIT,		/* object in initial unbound state */
-		FSCACHE_OBJECT_LOOKING_UP,	/* looking up object */
-		FSCACHE_OBJECT_CREATING,	/* creating object */
-
-		/* active states */
-		FSCACHE_OBJECT_AVAILABLE,	/* cleaning up object after creation */
-		FSCACHE_OBJECT_ACTIVE,		/* object is usable */
-		FSCACHE_OBJECT_INVALIDATING,	/* object is invalidating */
-		FSCACHE_OBJECT_UPDATING,	/* object is updating */
-
-		/* terminal states */
-		FSCACHE_OBJECT_DYING,		/* object waiting for accessors to finish */
-		FSCACHE_OBJECT_LC_DYING,	/* object cleaning up after lookup/create */
-		FSCACHE_OBJECT_ABORT_INIT,	/* abort the init state */
-		FSCACHE_OBJECT_RELEASING,	/* releasing object */
-		FSCACHE_OBJECT_RECYCLING,	/* retiring object */
-		FSCACHE_OBJECT_WITHDRAWING,	/* withdrawing object */
-		FSCACHE_OBJECT_DEAD,		/* object is now dead */
-		FSCACHE_OBJECT__NSTATES
-	} state;
-
+	const struct fscache_state *state;	/* Object state machine state */
+	const struct fscache_transition *oob_table; /* OOB state transition table */
 	int			debug_id;	/* debugging ID */
 	int			n_children;	/* number of child objects */
 	int			n_ops;		/* number of extant ops on object */
···
 	spinlock_t		lock;		/* state and operations lock */
 
 	unsigned long		lookup_jif;	/* time at which lookup started */
+	unsigned long		oob_event_mask;	/* OOB events this object is interested in */
 	unsigned long		event_mask;	/* events this object is interested in */
 	unsigned long		events;		/* events to be processed by this object
 						 * (order is important - using fls) */
···
 #define FSCACHE_OBJECT_LOCK		0	/* T if object is busy being processed */
 #define FSCACHE_OBJECT_PENDING_WRITE	1	/* T if object has pending write */
 #define FSCACHE_OBJECT_WAITING		2	/* T if object is waiting on its parent */
+#define FSCACHE_OBJECT_RETIRE		3	/* T if object should be retired */
+#define FSCACHE_OBJECT_IS_LIVE		4	/* T if object is not withdrawn or relinquished */
+#define FSCACHE_OBJECT_IS_LOOKED_UP	5	/* T if object has been looked up */
+#define FSCACHE_OBJECT_IS_AVAILABLE	6	/* T if object has become active */
 
 	struct list_head	cache_link;	/* link in cache->object_list */
 	struct hlist_node	cookie_link;	/* link in cookie->backing_objects */
···
 	loff_t			store_limit_l;	/* current storage limit */
 };
 
-extern const char *fscache_object_states[];
-
 extern void fscache_object_init(struct fscache_object *, struct fscache_cookie *,
 				struct fscache_cache *);
 
···
 
 static inline bool fscache_object_is_live(struct fscache_object *object)
 {
-	return object->state < FSCACHE_OBJECT_DYING;
+	return test_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
 }
 
 static inline bool fscache_object_is_dying(struct fscache_object *object)
···
 
 static inline bool fscache_object_is_available(struct fscache_object *object)
 {
-	return object->state >= FSCACHE_OBJECT_AVAILABLE;
+	return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
 }
 
 static inline bool fscache_object_is_active(struct fscache_object *object)