mtd: ubi: introduce pre-removal notification for UBI volumes

Introduce a new notification type UBI_VOLUME_SHUTDOWN to inform users
that a volume is just about to be removed.
This is needed because users (such as the NVMEM subsystem) expect that
at the time their removal function is called, the parenting device is
still available (for removal of sysfs nodes, for example, in case of
NVMEM which otherwise WARNs on volume removal).
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/build.c

@@ -93,7 +93,7 @@ static struct ubi_device *ubi_devices[UBI_MAX_DEVICES];
 /* Serializes UBI devices creations and removals */
 DEFINE_MUTEX(ubi_devices_mutex);
 
-/* Protects @ubi_devices and @ubi->ref_count */
+/* Protects @ubi_devices, @ubi->ref_count and @ubi->is_dead */
 static DEFINE_SPINLOCK(ubi_devices_lock);
 
 /* "Show" method for files in '/<sysfs>/class/ubi/' */
@@ -261,6 +261,9 @@ struct ubi_device *ubi_get_device(int ubi_num)
 
 	spin_lock(&ubi_devices_lock);
 	ubi = ubi_devices[ubi_num];
+	if (ubi && ubi->is_dead)
+		ubi = NULL;
+
 	if (ubi) {
 		ubi_assert(ubi->ref_count >= 0);
 		ubi->ref_count += 1;
@@ -298,7 +301,7 @@ struct ubi_device *ubi_get_by_major(int major)
 	spin_lock(&ubi_devices_lock);
 	for (i = 0; i < UBI_MAX_DEVICES; i++) {
 		ubi = ubi_devices[i];
-		if (ubi && MAJOR(ubi->cdev.dev) == major) {
+		if (ubi && !ubi->is_dead && MAJOR(ubi->cdev.dev) == major) {
 			ubi_assert(ubi->ref_count >= 0);
 			ubi->ref_count += 1;
 			get_device(&ubi->dev);
@@ -327,7 +330,7 @@ int ubi_major2num(int major)
 	for (i = 0; i < UBI_MAX_DEVICES; i++) {
 		struct ubi_device *ubi = ubi_devices[i];
 
-		if (ubi && MAJOR(ubi->cdev.dev) == major) {
+		if (ubi && !ubi->is_dead && MAJOR(ubi->cdev.dev) == major) {
 			ubi_num = ubi->ubi_num;
 			break;
 		}
@@ -514,7 +517,7 @@ static void ubi_free_volumes_from(struct ubi_device *ubi, int from)
 	int i;
 
 	for (i = from; i < ubi->vtbl_slots + UBI_INT_VOL_COUNT; i++) {
-		if (!ubi->volumes[i])
+		if (!ubi->volumes[i] || ubi->volumes[i]->is_dead)
 			continue;
 		ubi_eba_replace_table(ubi->volumes[i], NULL);
 		ubi_fastmap_destroy_checkmap(ubi->volumes[i]);
@@ -1099,7 +1102,6 @@ int ubi_detach_mtd_dev(int ubi_num, int anyway)
 		return -EINVAL;
 
 	spin_lock(&ubi_devices_lock);
-	put_device(&ubi->dev);
 	ubi->ref_count -= 1;
 	if (ubi->ref_count) {
 		if (!anyway) {
@@ -1110,6 +1112,13 @@ int ubi_detach_mtd_dev(int ubi_num, int anyway)
 		ubi_err(ubi, "%s reference count %d, destroy anyway",
 			ubi->ubi_name, ubi->ref_count);
 	}
+	ubi->is_dead = true;
+	spin_unlock(&ubi_devices_lock);
+
+	ubi_notify_all(ubi, UBI_VOLUME_SHUTDOWN, NULL);
+
+	spin_lock(&ubi_devices_lock);
+	put_device(&ubi->dev);
 	ubi_devices[ubi_num] = NULL;
 	spin_unlock(&ubi_devices_lock);
 

drivers/mtd/ubi/kapi.c

@@ -152,7 +152,7 @@ struct ubi_volume_desc *ubi_open_volume(int ubi_num, int vol_id, int mode)
 
 	spin_lock(&ubi->volumes_lock);
 	vol = ubi->volumes[vol_id];
-	if (!vol)
+	if (!vol || vol->is_dead)
 		goto out_unlock;
 
 	err = -EBUSY;

drivers/mtd/ubi/ubi.h

@@ -337,6 +337,7 @@ struct ubi_volume {
 	int writers;
 	int exclusive;
 	int metaonly;
+	bool is_dead;
 
 	int reserved_pebs;
 	int vol_type;
@@ -561,6 +562,7 @@ struct ubi_device {
 	spinlock_t volumes_lock;
 	int ref_count;
 	int image_seq;
+	bool is_dead;
 
 	int rsvd_pebs;
 	int avail_pebs;

drivers/mtd/ubi/vmt.c

@@ -59,7 +59,7 @@ static ssize_t vol_attribute_show(struct device *dev,
 	struct ubi_device *ubi = vol->ubi;
 
 	spin_lock(&ubi->volumes_lock);
-	if (!ubi->volumes[vol->vol_id]) {
+	if (!ubi->volumes[vol->vol_id] || ubi->volumes[vol->vol_id]->is_dead) {
 		spin_unlock(&ubi->volumes_lock);
 		return -ENODEV;
 	}
@@ -189,7 +189,7 @@ int ubi_create_volume(struct ubi_device *ubi, struct ubi_mkvol_req *req)
 
 	/* Ensure that the name is unique */
 	for (i = 0; i < ubi->vtbl_slots; i++)
-		if (ubi->volumes[i] &&
+		if (ubi->volumes[i] && !ubi->volumes[i]->is_dead &&
 		    ubi->volumes[i]->name_len == req->name_len &&
 		    !strcmp(ubi->volumes[i]->name, req->name)) {
 			ubi_err(ubi, "volume \"%s\" exists (ID %d)",
@@ -352,6 +352,19 @@ int ubi_remove_volume(struct ubi_volume_desc *desc, int no_vtbl)
 		err = -EBUSY;
 		goto out_unlock;
 	}
+
+	/*
+	 * Mark volume as dead at this point to prevent that anyone
+	 * can take a reference to the volume from now on.
+	 * This is necessary as we have to release the spinlock before
+	 * calling ubi_volume_notify.
+	 */
+	vol->is_dead = true;
+	spin_unlock(&ubi->volumes_lock);
+
+	ubi_volume_notify(ubi, vol, UBI_VOLUME_SHUTDOWN);
+
+	spin_lock(&ubi->volumes_lock);
 	ubi->volumes[vol_id] = NULL;
 	spin_unlock(&ubi->volumes_lock);
 

include/linux/mtd/ubi.h

@@ -192,6 +192,7 @@ struct ubi_device_info {
  *			or a volume was removed)
  * @UBI_VOLUME_RESIZED: a volume has been re-sized
  * @UBI_VOLUME_RENAMED: a volume has been re-named
+ * @UBI_VOLUME_SHUTDOWN: a volume is going to removed, shutdown users
  * @UBI_VOLUME_UPDATED: data has been written to a volume
  *
  * These constants define which type of event has happened when a volume
@@ -202,6 +203,7 @@ enum {
 	UBI_VOLUME_REMOVED,
 	UBI_VOLUME_RESIZED,
 	UBI_VOLUME_RENAMED,
+	UBI_VOLUME_SHUTDOWN,
 	UBI_VOLUME_UPDATED,
 };