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

[Anthony Krowiak]

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@xxxxxxxxxxxxxxx
> > Signed-off-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
> Please see my comment on patch 3.

See my response to your comment on patch 3:)