core: don't module_get() for internal buffer/trigger

If a driver module registerscreate its own preferred trigger or
buffer, we can't increment its own use count, or we won't be able to
unload the module.

This patch resolves the issue. Now the ZIO core doesn't increment the
use counter of the trigger or buffer, if it's owned by the device.

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
Acked-by: Alessandro Rubini <rubini@gnudd.com>

zio-sys.c

@@ -106,7 +106,7 @@ struct zio_device *zio_find_device(char *name, uint32_t dev_id)
 EXPORT_SYMBOL(zio_find_device);
 
 static inline struct zio_object_list_item *__zio_object_get(
-	struct zio_object_list *zobj_list, char *name)
+	struct zio_cset *cset, struct zio_object_list *zobj_list, char *name)
 {
 	struct zio_object_list_item *list_item;
 
@@ -115,44 +115,50 @@ static inline struct zio_object_list_item *__zio_object_get(
 	list_item = __find_by_name(zobj_list, name);
 	if (!list_item)
 		return NULL;
-	/* increment trigger usage to prevent rmmod */
-	if (!try_module_get(list_item->owner))
+	/* If different owner, try to increment its use count */
+	if (cset->zdev->owner != list_item->owner
+	    && !try_module_get(list_item->owner))
 		return NULL;
+
 	return list_item;
 }
-static struct zio_buffer_type *zio_buffer_get(char *name)
+static struct zio_buffer_type *zio_buffer_get(struct zio_cset *cset,
+					      char *name)
 {
 	struct zio_object_list_item *list_item;
 
 	if (!name)
 		return ERR_PTR(-EINVAL);
 
-	list_item = __zio_object_get(&zstat->all_buffer_types, name);
+	list_item = __zio_object_get(cset, &zstat->all_buffer_types, name);
 	if (!list_item)
 		return ERR_PTR(-ENODEV);
 	return container_of(list_item->obj_head, struct zio_buffer_type, head);
 }
-static inline void zio_buffer_put(struct zio_buffer_type *zbuf)
+static inline void zio_buffer_put(struct zio_buffer_type *zbuf,
+				  struct module *dev_owner)
 {
-	pr_debug("%s:%d %p\n", __func__, __LINE__, zbuf->owner);
-	module_put(zbuf->owner);
+	if (zbuf->owner != dev_owner)
+		module_put(zbuf->owner);
 }
-static struct zio_trigger_type *zio_trigger_get(char *name)
+static struct zio_trigger_type *zio_trigger_get(struct zio_cset *cset,
+						char *name)
 {
 	struct zio_object_list_item *list_item;
 
 	if (!name)
 		return ERR_PTR(-EINVAL);
 
-	list_item = __zio_object_get(&zstat->all_trigger_types, name);
+	list_item = __zio_object_get(cset, &zstat->all_trigger_types, name);
 	if (!list_item)
 		return ERR_PTR(-ENODEV);
 	return container_of(list_item->obj_head, struct zio_trigger_type, head);
 }
-static inline void zio_trigger_put(struct zio_trigger_type *trig)
+static inline void zio_trigger_put(struct zio_trigger_type *trig,
+				   struct module *dev_owner)
 {
-	pr_debug("%s:%d %p\n", __func__, __LINE__, trig->owner);
-	module_put(trig->owner);
+	if (trig->owner != dev_owner)
+		module_put(trig->owner);
 }
 
 static void __zio_internal_data_done(struct zio_cset *cset)
@@ -480,7 +486,7 @@ static int zio_change_current_trigger(struct zio_cset *cset, char *name)
 		return 0; /* is the current trigger */
 
 	/* get the new trigger */
-	trig = zio_trigger_get(name);
+	trig = zio_trigger_get(cset, name);
 	if (IS_ERR(trig))
 		return PTR_ERR(trig);
 	/* Create and register the new trigger instance */
@@ -495,7 +501,7 @@ static int zio_change_current_trigger(struct zio_cset *cset, char *name)
 	/* New ti successful created, remove the old ti */
 	__ti_unregister(trig_old, ti_old);
 	__ti_destroy(trig_old, ti_old);
-	zio_trigger_put(trig_old);
+	zio_trigger_put(trig_old, cset->zdev->owner);
 	/* Set new trigger*/
 	mb();
 	cset->trig = trig;
@@ -515,7 +521,7 @@ static int zio_change_current_trigger(struct zio_cset *cset, char *name)
 out_reg:
 	__ti_destroy(trig, ti);
 out:
-	zio_trigger_put(trig);
+	zio_trigger_put(trig, cset->zdev->owner);
 	return err;
 }
 
@@ -531,7 +537,7 @@ static int zio_change_current_buffer(struct zio_cset *cset, char *name)
 	if (unlikely(strcmp(name, cset->zbuf->head.name) == 0))
 		return 0; /* is the current buffer */
 
-	zbuf = zio_buffer_get(name);
+	zbuf = zio_buffer_get(cset, name);
 	if (IS_ERR(zbuf))
 		return PTR_ERR(zbuf);
 
@@ -573,7 +579,7 @@ static int zio_change_current_buffer(struct zio_cset *cset, char *name)
 
 	kfree(bi_vector);
 	cset->zbuf = zbuf;
-	zio_buffer_put(zbuf_old);
+	zio_buffer_put(zbuf_old, cset->zdev->owner);
 
 	return 0;
 
@@ -584,7 +590,7 @@ out_create:
 	}
 	kfree(bi_vector);
 out:
-	zio_buffer_put(zbuf);
+	zio_buffer_put(zbuf, cset->zdev->owner);
 	return err;
 }
 
@@ -1775,11 +1781,11 @@ static int cset_set_trigger(struct zio_cset *cset)
 	if (cset->zdev->preferred_trigger) /* preferred device trigger */
 		name = cset->zdev->preferred_trigger;
 
-	trig = zio_trigger_get(name);
+	trig = zio_trigger_get(cset, name);
 	if (IS_ERR(trig)) {
 		dev_dbg(&cset->head.dev, "no trigger \"%s\" (error %li), using "
 			 "default\n", name, PTR_ERR(trig));
-		trig = zio_trigger_get(ZIO_DEFAULT_TRIGGER);
+		trig = zio_trigger_get(cset, ZIO_DEFAULT_TRIGGER);
 	}
 	if (IS_ERR(trig))
 		return PTR_ERR(trig);
@@ -1800,11 +1806,11 @@ static int cset_set_buffer(struct zio_cset *cset)
 	if (cset->zdev->preferred_buffer) /* preferred device buffer */
 		name = cset->zdev->preferred_buffer;
 
-	zbuf = zio_buffer_get(name);
+	zbuf = zio_buffer_get(cset, name);
 	if (IS_ERR(zbuf)) {
 		dev_dbg(&cset->head.dev, "no buffer \"%s\" (error %li), using "
 			 "default\n", name, PTR_ERR(zbuf));
-		zbuf = zio_buffer_get(ZIO_DEFAULT_BUFFER);
+		zbuf = zio_buffer_get(cset, ZIO_DEFAULT_BUFFER);
 	}
 	if (IS_ERR(zbuf))
 		return PTR_ERR(zbuf);
@@ -1933,9 +1939,9 @@ out_n_chan:
 out_tr:
 	__ti_destroy(cset->trig, ti);
 out_trig:
-	zio_trigger_put(cset->trig);
+	zio_trigger_put(cset->trig, cset->zdev->owner);
 	cset->trig = NULL;
-	zio_buffer_put(cset->zbuf);
+	zio_buffer_put(cset->zbuf, cset->zdev->owner);
 	cset->zbuf = NULL;
 out_buf:
 	device_unregister(&cset->head.dev);
@@ -1969,11 +1975,11 @@ static void cset_unregister(struct zio_cset *cset)
 	/* destroy instance and decrement trigger usage */
 	__ti_unregister(cset->trig, cset->ti);
 	__ti_destroy(cset->trig,  cset->ti);
-	zio_trigger_put(cset->trig);
+	zio_trigger_put(cset->trig, cset->zdev->owner);
 	cset->trig = NULL;
 
 	/* decrement buffer usage */
-	zio_buffer_put(cset->zbuf);
+	zio_buffer_put(cset->zbuf, cset->zdev->owner);
 	cset->zbuf = NULL;
 
 	device_unregister(&cset->head.dev);