linux-kernel - [PATCH] block: fix kobject double initialization in add

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Message-Id: <20250807072056.2627592-1-zhengqixing@huaweicloud.com>
Date: Thu,  7 Aug 2025 15:20:56 +0800
From: Zheng Qixing <zhengqixing@...weicloud.com>
To: axboe@...nel.dk
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	houtao1@...wei.com,
	zhengqixing@...wei.com
Subject: [PATCH] block: fix kobject double initialization in add_disk

From: Zheng Qixing <zhengqixing@...wei.com>

Device-mapper can call add_disk() multiple times for the same gendisk
due to its two-phase creation process (dm create + dm load). This leads
to kobject double initialization errors when the underlying iSCSI devices
become temporarily unavailable and then reappear.

However, if the first add_disk() call fails and is retried, the queue_kobj
gets initialized twice, causing:

kobject: kobject (ffff88810c27bb90): tried to init an initialized object,
something is seriously wrong.
 Call Trace:
  <TASK>
  dump_stack_lvl+0x5b/0x80
  kobject_init.cold+0x43/0x51
  blk_register_queue+0x46/0x280
  add_disk_fwnode+0xb5/0x280
  dm_setup_md_queue+0x194/0x1c0
  table_load+0x297/0x2d0
  ctl_ioctl+0x2a2/0x480
  dm_ctl_ioctl+0xe/0x20
  __x64_sys_ioctl+0xc7/0x110
  do_syscall_64+0x72/0x390
  entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fix this by separating kobject initialization from sysfs registration:
 - Initialize queue_kobj early during gendisk allocation
 - add_disk() only adds the already-initialized kobject to sysfs
 - del_gendisk() removes from sysfs but doesn't destroy the kobject
 - Final cleanup happens when the disk is released

Fixes: 2bd85221a625 ("block: untangle request_queue refcounting from sysfs")
Reported-by: Li Lingfeng <lilingfeng3@...wei.com>
Closes: https://lore.kernel.org/all/83591d0b-2467-433c-bce0-5581298eb161@huawei.com/
Signed-off-by: Zheng Qixing <zhengqixing@...wei.com>
---
 block/blk-sysfs.c | 4 +---
 block/blk.h       | 1 +
 block/genhd.c     | 2 ++
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 396cded255ea..37d8654faff9 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -847,7 +847,7 @@ static void blk_queue_release(struct kobject *kobj)
 	/* nothing to do here, all data is associated with the parent gendisk */
 }
 
-static const struct kobj_type blk_queue_ktype = {
+const struct kobj_type blk_queue_ktype = {
 	.default_groups = blk_queue_attr_groups,
 	.sysfs_ops	= &queue_sysfs_ops,
 	.release	= blk_queue_release,
@@ -875,7 +875,6 @@ int blk_register_queue(struct gendisk *disk)
 	struct request_queue *q = disk->queue;
 	int ret;
 
-	kobject_init(&disk->queue_kobj, &blk_queue_ktype);
 	ret = kobject_add(&disk->queue_kobj, &disk_to_dev(disk)->kobj, "queue");
 	if (ret < 0)
 		goto out_put_queue_kobj;
@@ -986,5 +985,4 @@ void blk_unregister_queue(struct gendisk *disk)
 		elevator_set_none(q);
 
 	blk_debugfs_remove(disk);
-	kobject_put(&disk->queue_kobj);
 }
diff --git a/block/blk.h b/block/blk.h
index 0a2eccf28ca4..46f566f9b126 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -29,6 +29,7 @@ struct elevator_tags;
 /* Max future timer expiry for timeouts */
 #define BLK_MAX_TIMEOUT		(5 * HZ)
 
+extern const struct kobj_type blk_queue_ktype;
 extern struct dentry *blk_debugfs_root;
 
 struct blk_flush_queue {
diff --git a/block/genhd.c b/block/genhd.c
index c26733f6324b..9bbc38d12792 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1303,6 +1303,7 @@ static void disk_release(struct device *dev)
 	disk_free_zone_resources(disk);
 	xa_destroy(&disk->part_tbl);
 
+	kobject_put(&disk->queue_kobj);
 	disk->queue->disk = NULL;
 	blk_put_queue(disk->queue);
 
@@ -1486,6 +1487,7 @@ struct gendisk *__alloc_disk_node(struct request_queue *q, int node_id,
 	INIT_LIST_HEAD(&disk->slave_bdevs);
 #endif
 	mutex_init(&disk->rqos_state_mutex);
+	kobject_init(&disk->queue_kobj, &blk_queue_ktype);
 	return disk;
 
 out_erase_part0:
-- 
2.39.2