Re: [PATCH v2] block: fix kobject double initialization in add_disk

[Ming Lei]

On Fri, Aug 08, 2025 at 01:36:09PM +0800, Zheng Qixing wrote:
> From: Zheng Qixing <zhengqixing@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/83591d0b-2467-433c-bce0-5581298eb161@xxxxxxxxxx/
> Signed-off-by: Zheng Qixing <zhengqixing@xxxxxxxxxx>

Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>

Thanks,
Ming