fscache fixes

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Merge tag 'fscache-fixes-20180725' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull fscache/cachefiles fixes from David Howells:

 - Allow cancelled operations to be queued so they can be cleaned up.

 - Fix a refcounting bug in the monitoring of reads on backend files
   whereby a race can occur between monitor objects being listed for
   work, the work processing being queued and the work processor running
   and destroying the monitor objects.

 - Fix a ref overput in object attachment, whereby a tentatively
   considered object is put in error handling without first being 'got'.

 - Fix a missing clear of the CACHEFILES_OBJECT_ACTIVE flag whereby an
   assertion occurs when we retry because it seems the object is now
   active.

 - Wait rather BUG'ing on an object collision in the depths of
   cachefiles as the active object should be being cleaned up - also
   depends on the one above.

* tag 'fscache-fixes-20180725' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  cachefiles: Wait rather than BUG'ing on "Unexpected object collision"
  cachefiles: Fix missing clear of the CACHEFILES_OBJECT_ACTIVE flag
  fscache: Fix reference overput in fscache_attach_object() error handling
  cachefiles: Fix refcounting bug in backing-file read monitoring
  fscache: Allow cancelled operations to be enqueued

fs/cachefiles/bind.c

@@ -218,7 +218,8 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache)
 			   "%s",
 			   fsdef->dentry->d_sb->s_id);
 
-	fscache_object_init(&fsdef->fscache, NULL, &cache->cache);
+	fscache_object_init(&fsdef->fscache, &fscache_fsdef_index,
+			    &cache->cache);
 
 	ret = fscache_add_cache(&cache->cache, &fsdef->fscache, cache->tag);
 	if (ret < 0)

fs/cachefiles/namei.c

@@ -186,12 +186,12 @@ try_again:
 	 * need to wait for it to be destroyed */
 wait_for_old_object:
 	trace_cachefiles_wait_active(object, dentry, xobject);
+	clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags);
 
 	if (fscache_object_is_live(&xobject->fscache)) {
 		pr_err("\n");
 		pr_err("Error: Unexpected object collision\n");
 		cachefiles_printk_object(object, xobject);
-		BUG();
 	}
 	atomic_inc(&xobject->usage);
 	write_unlock(&cache->active_lock);
@@ -248,7 +248,6 @@ wait_for_old_object:
 	goto try_again;
 
 requeue:
-	clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags);
 	cache->cache.ops->put_object(&xobject->fscache, cachefiles_obj_put_wait_timeo);
 	_leave(" = -ETIMEDOUT");
 	return -ETIMEDOUT;

fs/cachefiles/rdwr.c

@@ -27,6 +27,7 @@ static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
 	struct cachefiles_one_read *monitor =
 		container_of(wait, struct cachefiles_one_read, monitor);
 	struct cachefiles_object *object;
+	struct fscache_retrieval *op = monitor->op;
 	struct wait_bit_key *key = _key;
 	struct page *page = wait->private;
 
@@ -51,16 +52,22 @@ static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
 	list_del(&wait->entry);
 
 	/* move onto the action list and queue for FS-Cache thread pool */
-	ASSERT(monitor->op);
+	ASSERT(op);
 
-	object = container_of(monitor->op->op.object,
-			      struct cachefiles_object, fscache);
+	/* We need to temporarily bump the usage count as we don't own a ref
+	 * here otherwise cachefiles_read_copier() may free the op between the
+	 * monitor being enqueued on the op->to_do list and the op getting
+	 * enqueued on the work queue.
+	 */
+	fscache_get_retrieval(op);
 
+	object = container_of(op->op.object, struct cachefiles_object, fscache);
 	spin_lock(&object->work_lock);
-	list_add_tail(&monitor->op_link, &monitor->op->to_do);
+	list_add_tail(&monitor->op_link, &op->to_do);
 	spin_unlock(&object->work_lock);
 
-	fscache_enqueue_retrieval(monitor->op);
+	fscache_enqueue_retrieval(op);
+	fscache_put_retrieval(op);
 	return 0;
 }
 

fs/fscache/cache.c

@@ -220,6 +220,7 @@ int fscache_add_cache(struct fscache_cache *cache,
 {
 	struct fscache_cache_tag *tag;
 
+	ASSERTCMP(ifsdef->cookie, ==, &fscache_fsdef_index);
 	BUG_ON(!cache->ops);
 	BUG_ON(!ifsdef);
 
@@ -248,7 +249,6 @@ int fscache_add_cache(struct fscache_cache *cache,
 	if (!cache->kobj)
 		goto error;
 
-	ifsdef->cookie = &fscache_fsdef_index;
 	ifsdef->cache = cache;
 	cache->fsdef = ifsdef;
 

fs/fscache/cookie.c

@@ -516,6 +516,7 @@ static int fscache_alloc_object(struct fscache_cache *cache,
 		goto error;
 	}
 
+	ASSERTCMP(object->cookie, ==, cookie);
 	fscache_stat(&fscache_n_object_alloc);
 
 	object->debug_id = atomic_inc_return(&fscache_object_debug_id);
@@ -571,6 +572,8 @@ static int fscache_attach_object(struct fscache_cookie *cookie,
 
 	_enter("{%s},{OBJ%x}", cookie->def->name, object->debug_id);
 
+	ASSERTCMP(object->cookie, ==, cookie);
+
 	spin_lock(&cookie->lock);
 
 	/* there may be multiple initial creations of this object, but we only
@@ -610,9 +613,7 @@ static int fscache_attach_object(struct fscache_cookie *cookie,
 		spin_unlock(&cache->object_list_lock);
 	}
 
-	/* attach to the cookie */
-	object->cookie = cookie;
-	fscache_cookie_get(cookie, fscache_cookie_get_attach_object);
+	/* Attach to the cookie.  The object already has a ref on it. */
 	hlist_add_head(&object->cookie_link, &cookie->backing_objects);
 
 	fscache_objlist_add(object);

fs/fscache/object.c

@@ -327,6 +327,7 @@ void fscache_object_init(struct fscache_object *object,
 	object->store_limit_l = 0;
 	object->cache = cache;
 	object->cookie = cookie;
+	fscache_cookie_get(cookie, fscache_cookie_get_attach_object);
 	object->parent = NULL;
 #ifdef CONFIG_FSCACHE_OBJECT_LIST
 	RB_CLEAR_NODE(&object->objlist_link);

fs/fscache/operation.c

@@ -70,7 +70,8 @@ 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) {
@@ -499,7 +500,8 @@ 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);