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

[Anthony Krowiak <akrowiak@linux.ibm.com>]

On 8/11/26 2:03 PM, Matthew Rosato wrote:
> 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@vger.kernel.org
>> Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
> Please see my comment on patch 3.

See my response to your comment on patch 3:)