Re: [PATCH 1/2] ublk: publish a new device by its id only once it is set up

[Ming Lei <tom.leiming@gmail.com>]

On Thu, Nov 05, 2026 at 12:25:05AM +0500, Mark Korenberg via B4 Relay wrote:
> From: Mark Korenberg <socketpair@gmail.com>
> 
> ADD_DEV stores the device in ublk_index_idr when it allocates the id,
> and control commands find it there as soon as ublk_add_chdev() has
> initialized its struct device, before the char device is added. If
> dev_set_name() or cdev_device_add() then fails, ublk_add_chdev() drops
> the initial reference to free the device. A DEL_DEV that found the
> device meanwhile waits for ublk_ctl_mutex, then calls ublk_remove():
> cdev_device_del() of a device that was never added, and a second put of
> the initial reference, which frees the device under the callers still
> holding references.
> 
> Reserve the id with a NULL entry, which idr_find() and the idr iterators
> skip, and store the device once ublk_add_chdev() succeeded.
> 
> Fixes: 71f28f3136af ("ublk_drv: add io_uring based userspace block driver")
> Signed-off-by: Mark Korenberg <socketpair@gmail.com>

Reviewed-by: Ming Lei <tom.leiming@gmail.com>

Thanks,
Ming