Re: [PATCH v11 04/14] s390/zcrypt: driver callback to indicate resource in use

[Tony Krowiak]

On 11/13/20 7:00 PM, Halil Pasic wrote:
> On Fri, 13 Nov 2020 16:30:31 -0500
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > We will be using the mutex_trylock() function in our sysfs
> > assignment
> > interfaces which make the call to the AP bus to check permissions (which
> > also
> > locks ap_perms). If the mutex_trylock() fails, we return from the assignment
> > function with -EBUSY. This should resolve that potential deadlock issue.
> It resolves the deadlock issue only if in_use() is also doing
> mutex_trylock(), but the if in_use doesn't take the lock it
> needs to back off (and so does it's client code) i.e. a boolean as
> return value won't do.

Makes sense. I'll change the in_use callback to return an int and use
mutex_trylock() for the vfio_ap_mdev_in_use() function. If the lock
can not be obtained, the function will return -EBUSY.

> Regards,
> Halil