Subject: [PATCH 2/2] mtd: blktrans: call add disks after mtd device

From: Daniel Golle <[email-masked]>
Date: Wed, 7 Apr 2021 22:45:54 +0100

Calling device_add_disk while holding mtd_table_mutex leads
to deadlock in case part_bits!=0 as block partition parsers
will try to open the newly created disks, trying to acquire
mutex once again.
Move device_add_disk to additional function called after
add partitions of an MTD device have been added and locks
have been released.

Signed-off-by: Daniel Golle <[email-masked]>
---
 drivers/mtd/mtd_blkdevs.c    | 33 ++++++++++++++++++++++++++-------
 drivers/mtd/mtdcore.c        |  3 +++
 include/linux/mtd/blktrans.h |  1 +
 3 files changed, 30 insertions(+), 7 deletions(-)

--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -457,13 +457,6 @@ int add_mtd_blktrans_dev(struct mtd_blkt
 	if (new->readonly)
 		set_disk_ro(gd, 1);
 
-	device_add_disk(&new->mtd->dev, gd, NULL);
-
-	if (new->disk_attributes) {
-		ret = sysfs_create_group(&disk_to_dev(gd)->kobj,
-					new->disk_attributes);
-		WARN_ON(ret);
-	}
 	return 0;
 error4:
 	kfree(new->tag_set);
@@ -475,6 +468,27 @@ error1:
 	return ret;
 }
 
+void register_mtd_blktrans_devs(void)
+{
+	struct mtd_blktrans_ops *tr;
+	struct mtd_blktrans_dev *dev, *next;
+	int ret;
+
+	list_for_each_entry(tr, &blktrans_majors, list) {
+		list_for_each_entry_safe(dev, next, &tr->devs, list) {
+			if (dev->disk->flags & GENHD_FL_UP)
+				continue;
+
+			device_add_disk(&dev->mtd->dev, dev->disk, NULL);
+			if (dev->disk_attributes) {
+				ret = sysfs_create_group(&disk_to_dev(dev->disk)->kobj,
+							dev->disk_attributes);
+				WARN_ON(ret);
+			}
+		}
+	}
+}
+
 int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old)
 {
 	unsigned long flags;
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -32,6 +32,7 @@
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/partitions.h>
+#include <linux/mtd/blktrans.h>
 
 #include "mtdcore.h"
 
@@ -930,6 +931,8 @@ int mtd_device_parse_register(struct mtd
 		register_reboot_notifier(&mtd->reboot_notifier);
 	}
 
+	register_mtd_blktrans_devs();
+
 out:
 	if (ret && device_is_registered(&mtd->dev))
 		del_mtd_device(mtd);
--- a/include/linux/mtd/blktrans.h
+++ b/include/linux/mtd/blktrans.h
@@ -76,6 +76,6 @@ extern int deregister_mtd_blktrans(struc
 extern int add_mtd_blktrans_dev(struct mtd_blktrans_dev *dev);
 extern int del_mtd_blktrans_dev(struct mtd_blktrans_dev *dev);
 extern int mtd_blktrans_cease_background(struct mtd_blktrans_dev *dev);
-
+extern void register_mtd_blktrans_devs(void);
 
 #endif /* __MTD_TRANS_H__ */