Re: [PATCH v2 7/8] s390/vfio-ap: Fix required lock not held during display of sysfs status attribute

[Matthew Rosato]

On 8/10/26 3:22 PM, Anthony Krowiak wrote:
> The status_show function that supports display of the status attribute of
> the devices in /sys/bus/ap/devices calls the vfio_ap_mdev_for_queue
> function which iterates the matrix_dev->mdev_list to find the object
> representing the queue device whose status is to be displayed. In order to
> traverse this list, the matrix_dev->guests_lock mutex must be held which is
> not the case.
> 
> To fix this, the guests_lock mutex is taken prior to taking the
> matrix_dev->mdevs_lock mutex in the status_show function. It is taken
> there rather than the vfio_ap_mdev_for_queue function - where it is
> needed - because it must be taken prior to the mdevs_lock mutex in order to
> adhere to the proper locking order and prevent a lockdep splat; also
> because the mdevs_lock is needed there to access fields within
> the matrix_mdev object in that function.
> 
> Fixes: f139862b92cf ("s390/vfio-ap: add status attribute to AP queue device's sysfs dir")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
Please see my comment on patch 3.