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 <dhowells@redhat.com>
Tested-By: Milosz Tanski <milosz@adfin.com>
Acked-by: Jeff Layton <jlayton@redhat.com>

1 files changed, 527 insertions, 491 deletions

diff --git a/fs/fscache/object.c b/fs/fscache/object.c
index 863f6873c0f0..8f17debd7979 100644
--- a/fs/fscache/object.c
+++ b/fs/fscache/object.c
@@ -15,52 +15,133 @@
 #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",
+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);
+
+#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 }
 };
-EXPORT_SYMBOL(fscache_object_states);
-
-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",
+
+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 *);
 
 /*
@@ -83,281 +164,102 @@ static inline void fscache_done_parent_op(struct fscache_object *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);
-
-	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;
-
-		/* 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);
+	       object->debug_id, object->state->name, object->events);
+
+	event_mask = object->event_mask;
+restart:
+	object->event_mask = 0; /* Mask normal event handling */
+	state = object->state;
+restart_masked:
+	events = object->events;
+
+	/* 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;
-	}
-
-	/* 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;
-	}
+execute_work_state:
+	_debug("{OBJ%x} exec %s", object->debug_id, state->name);
 
-	/* 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;
+	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;
 	}
 
-change_state:
-	spin_lock(&object->lock);
-	object->state = new_state;
-	spin_unlock(&object->lock);
+	_debug("{OBJ%x} %s -> %s",
+	       object->debug_id, state->name, new_state->name);
+	object->state = state = new_state;
 
-done:
-	_leave(" [->%s]", fscache_object_states[object->state]);
-	return;
+	if (state->work) {
+		if (unlikely(state->work == ((void *)2UL))) {
+			_leave(" [dead]");
+			return;
+		}
+		goto restart_masked;
+	}
 
-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();
+	/* Transited to wait state */
+	event_mask = object->oob_event_mask;
+	for (t = state->transitions; t->events; t++)
+		event_mask |= t->events;
+
+unmask_events:
+	object->event_mask = event_mask;
+	smp_mb();
+	events = object->events;
+	if (events & event_mask)
+		goto restart;
+	_leave(" [msk %lx]", event_mask);
 }
 
 /*
@@ -372,11 +274,8 @@ static void fscache_object_work_func(struct work_struct *work)
 	_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);
 }
 
@@ -395,9 +294,13 @@ void fscache_object_init(struct fscache_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);
@@ -407,17 +310,48 @@ void fscache_object_init(struct fscache_object *object,
 	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
  * - check the specified object's parent to see if we can make use of it
  *   immediately to do a creation
@@ -426,74 +360,78 @@ EXPORT_SYMBOL(fscache_object_init);
  * - 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);
-		}
+		_leave(" [no parent]");
+		return transit_to(DETACH_FROM_COOKIE);
+	}
 
-		spin_unlock(&parent->lock);
-		spin_unlock(&object->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);
 	}
 
-	spin_unlock(&object->cookie->parent->lock);
-	spin_unlock(&object->cookie->lock);
+	/* 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);
 }
 
 /*
@@ -503,15 +441,17 @@ static void fscache_initialise_object(struct fscache_object *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);
+
+	object->oob_table = fscache_osm_lookup_oob;
 
-	parent = object->parent;
 	ASSERT(parent != NULL);
 	ASSERTCMP(parent->n_ops, >, 0);
 	ASSERTCMP(parent->n_obj_ops, >, 0);
@@ -521,10 +461,8 @@ static void fscache_lookup_object(struct fscache_object *object)
 
 	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\"",
@@ -543,10 +481,17 @@ static void fscache_lookup_object(struct fscache_object *object)
 		/* 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);
 }
 
 /**
@@ -560,32 +505,20 @@ 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]);
+	_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);
@@ -604,37 +537,30 @@ 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]);
+	_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);
-
-		object->state = FSCACHE_OBJECT_AVAILABLE;
-		spin_unlock(&object->lock);
+		/* We do (presumably) have data */
+		clear_bit_unlock(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
 
-		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("");
 }
@@ -643,15 +569,18 @@ EXPORT_SYMBOL(fscache_obtained_object);
 /*
  * 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) {
@@ -667,72 +596,117 @@ static void fscache_object_available(struct fscache_object *object)
 	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)
 {
-	struct fscache_object *parent = object->parent;
-	struct fscache_cache *cache = object->cache;
+	_enter("{OBJ%x},%d", object->debug_id, event);
 
-	_enter("{OBJ%x,%d}", object->debug_id, object->n_children);
+	if (!fscache_enqueue_dependents(object, FSCACHE_OBJECT_EV_PARENT_READY))
+		return NO_TRANSIT; /* Not finished; requeue */
+	return transit_to(WAIT_FOR_CMD);
+}
 
-	ASSERTCMP(object->cookie, ==, NULL);
-	ASSERT(hlist_unhashed(&object->cookie_link));
+/*
+ * 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;
 
-	spin_lock(&cache->object_list_lock);
-	list_del_init(&object->cache_link);
-	spin_unlock(&cache->object_list_lock);
+	_enter("{OBJ%x},%d", object->debug_id, event);
 
-	fscache_stat(&fscache_n_cop_drop_object);
-	cache->ops->drop_object(object);
-	fscache_stat_d(&fscache_n_cop_drop_object);
+	object->oob_event_mask = 0;
 
-	if (parent) {
-		_debug("release parent OBJ%x {%d}",
-		       parent->debug_id, parent->n_children);
+	fscache_stat(&fscache_n_cop_lookup_complete);
+	object->cache->ops->lookup_complete(object);
+	fscache_stat_d(&fscache_n_cop_lookup_complete);
 
-		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;
+	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);
 
-	/* this just shifts the object release to the work processor */
-	fscache_put_object(object);
+	if (wake_looking_up)
+		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
+	wake_up_bit(&cookie->flags, FSCACHE_COOKIE_CREATING);
 
-	_leave("");
+	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);
 }
 
 /*
- * release or recycle an object that the netfs has discarded
+ * Kill dependent objects.
  */
-static void fscache_release_object(struct fscache_object *object)
+static const struct fscache_state *fscache_kill_dependents(struct fscache_object *object,
+							   int event)
 {
-	_enter("");
+	_enter("{OBJ%x},%d", object->debug_id, event);
 
-	fscache_drop_object(object);
+	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 void fscache_withdraw_object(struct fscache_object *object)
+static const struct fscache_state *fscache_detach_from_cookie(struct fscache_object *object,
+							      int event)
 {
 	struct fscache_cookie *cookie;
-	bool detached;
+	bool detached = false, awaken = false;
 
-	_enter("");
+	_enter("{OBJ%x},%d", object->debug_id, event);
 
 	spin_lock(&object->lock);
 	cookie = object->cookie;
@@ -742,14 +716,15 @@ static void fscache_withdraw_object(struct fscache_object *object)
 		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);
+			if (test_and_clear_bit(FSCACHE_COOKIE_INVALIDATING,
+					       &cookie->flags))
+				awaken = true;
 			detached = true;
 		}
 		spin_unlock(&cookie->lock);
@@ -760,37 +735,62 @@ static void fscache_withdraw_object(struct fscache_object *object)
 
 	spin_unlock(&object->lock);
 
-	fscache_drop_object(object);
+	if (awaken)
+		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_INVALIDATING);
+
+	fscache_stat(&fscache_n_object_dead);
+	_leave("");
+	return transit_to(DROP_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)
+ * Drop an object's attachments
+ */
+static const struct fscache_state *fscache_drop_object(struct fscache_object *object,
+						       int event)
 {
-	bool enqueue = false;
+	struct fscache_object *parent = object->parent;
+	struct fscache_cache *cache = object->cache;
 
-	_enter(",OBJ%x", object->debug_id);
+	_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);
-	if (object->state < FSCACHE_OBJECT_WITHDRAWING) {
-		object->state = FSCACHE_OBJECT_WITHDRAWING;
-		enqueue = true;
-	}
 	spin_unlock(&object->lock);
 
-	if (enqueue)
-		fscache_enqueue_object(object);
+	/* 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);
+
+	fscache_stat(&fscache_n_cop_drop_object);
+	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);
+
+		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;
+	}
+
+	/* this just shifts the object release to the work processor */
+	fscache_put_object(object);
+	fscache_stat(&fscache_n_object_dead);
 
 	_leave("");
+	return transit_to(OBJECT_DEAD);
 }
 
 /*
@@ -807,7 +807,7 @@ static int fscache_get_object(struct fscache_object *object)
 }
 
 /*
- * discard a ref on a work item
+ * Discard a ref on an object
  */
 static void fscache_put_object(struct fscache_object *object)
 {
@@ -839,7 +839,7 @@ void fscache_enqueue_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.
  *
@@ -867,18 +867,21 @@ bool fscache_object_sleep_till_congested(signed long *timeoutp)
 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);
 
@@ -887,23 +890,23 @@ static void fscache_enqueue_dependents(struct fscache_object *object)
 				 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);
 
@@ -963,12 +966,14 @@ EXPORT_SYMBOL(fscache_check_aux);
 /*
  * 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);
@@ -978,9 +983,9 @@ static void fscache_invalidate_object(struct fscache_object *object)
 	/* 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);
@@ -1001,13 +1006,44 @@ static void fscache_invalidate_object(struct fscache_object *object)
 	/* 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);
 }