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, 9 insertions, 13 deletions

diff --git a/fs/fscache/operation.c b/fs/fscache/operation.c
index ccf02194e7a6..4da211b21ddf 100644
--- a/fs/fscache/operation.c
+++ b/fs/fscache/operation.c
@@ -119,7 +119,7 @@ int fscache_submit_exclusive_op(struct fscache_object *object,
                 /* 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 */
@@ -144,7 +144,7 @@ int fscache_submit_exclusive_op(struct fscache_object *object,
  */
 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;
@@ -155,11 +155,8 @@ static void fscache_report_unexpected_submission(struct fscache_object *object,
         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",
@@ -190,7 +187,7 @@ static void fscache_report_unexpected_submission(struct fscache_object *object,
 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}",
@@ -226,16 +223,14 @@ int fscache_submit_op(struct fscache_object *object,
                         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;
@@ -266,13 +261,14 @@ void fscache_abort_object(struct fscache_object *object)
 
 /*
  * 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,
                                 struct fscache_operation, pend_link);