From 924731fbed3247e3b82b8ab17db587ee28c2e781 Mon Sep 17 00:00:00 2001
From: Daniel Golle <daniel@makrotopia.org>
Date: Tue, 19 Dec 2023 02:33:24 +0000
Subject: [PATCH 5/8] 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 | 19 ++++++++++++++-----
 drivers/mtd/ubi/kapi.c  |  2 +-
 drivers/mtd/ubi/ubi.h   |  2 ++
 drivers/mtd/ubi/vmt.c   | 17 +++++++++++++++--
 include/linux/mtd/ubi.h |  2 ++
 5 files changed, 34 insertions(+), 8 deletions(-)

--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -91,7 +91,7 @@ static struct ubi_device *ubi_devices[UB
 /* 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/' */
@@ -259,6 +259,9 @@ struct ubi_device *ubi_get_device(int ub
 
 	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;
@@ -296,7 +299,7 @@ struct ubi_device *ubi_get_by_major(int
 	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);
@@ -325,7 +328,7 @@ 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;
 		}
@@ -512,7 +515,7 @@ static void ubi_free_volumes_from(struct
 	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]);
@@ -1094,7 +1097,6 @@ int ubi_detach_mtd_dev(int ubi_num, int
 		return -EINVAL;
 
 	spin_lock(&ubi_devices_lock);
-	put_device(&ubi->dev);
 	ubi->ref_count -= 1;
 	if (ubi->ref_count) {
 		if (!anyway) {
@@ -1105,6 +1107,13 @@ int ubi_detach_mtd_dev(int ubi_num, int
 		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);
 
--- a/drivers/mtd/ubi/kapi.c
+++ b/drivers/mtd/ubi/kapi.c
@@ -152,7 +152,7 @@ struct ubi_volume_desc *ubi_open_volume(
 
 	spin_lock(&ubi->volumes_lock);
 	vol = ubi->volumes[vol_id];
-	if (!vol)
+	if (!vol || vol->is_dead)
 		goto out_unlock;
 
 	err = -EBUSY;
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -345,6 +345,7 @@ struct ubi_volume {
 	int writers;
 	int exclusive;
 	int metaonly;
+	bool is_dead;
 
 	int reserved_pebs;
 	int vol_type;
@@ -564,6 +565,7 @@ struct ubi_device {
 	spinlock_t volumes_lock;
 	int ref_count;
 	int image_seq;
+	bool is_dead;
 
 	int rsvd_pebs;
 	int avail_pebs;
--- a/drivers/mtd/ubi/vmt.c
+++ b/drivers/mtd/ubi/vmt.c
@@ -59,7 +59,7 @@ static ssize_t vol_attribute_show(struct
 	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
 
 	/* 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_
 		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);
 
--- a/include/linux/mtd/ubi.h
+++ b/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,
 };
 
