fscache: Allow cancelled operations to be enqueued

BugLink: https://bugs.launchpad.net/bugs/1774336

Alter the state-check assertion in fscache_enqueue_operation() to allow
cancelled operations to be given processing time so they can be cleaned up.

Also fix a debugging statement that was requiring such operations to have
an object assigned.

Fixes: 9ae326a6 ("CacheFiles: A cache that backs onto a mounted filesystem")
Reported-by: Kiran Kumar Modukuri <kiran.modukuri@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
(cherry picked from commit d0eb06af)
Signed-off-by: Daniel Axtens <daniel.axtens@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

fs/fscache/operation.c

@@ -66,7 +66,8 @@ void fscache_enqueue_operation(struct fscache_operation *op)
 	ASSERT(op->processor != NULL);
 	ASSERT(fscache_object_is_available(op->object));
 	ASSERTCMP(atomic_read(&op->usage), >, 0);
-	ASSERTCMP(op->state, ==, FSCACHE_OP_ST_IN_PROGRESS);
+	ASSERTIFCMP(op->state != FSCACHE_OP_ST_IN_PROGRESS,
+		    op->state, ==,  FSCACHE_OP_ST_CANCELLED);
 
 	fscache_stat(&fscache_n_op_enqueue);
 	switch (op->flags & FSCACHE_OP_TYPE) {
@@ -481,7 +482,8 @@ void fscache_put_operation(struct fscache_operation *op)
 	struct fscache_cache *cache;
 
 	_enter("{OBJ%x OP%x,%d}",
-	       op->object->debug_id, op->debug_id, atomic_read(&op->usage));
+	       op->object ? op->object->debug_id : 0,
+	       op->debug_id, atomic_read(&op->usage));
 
 	ASSERTCMP(atomic_read(&op->usage), >, 0);