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

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Message-ID: <20201114010020.381277c2.pasic@linux.ibm.com>
Date:   Sat, 14 Nov 2020 01:00:20 +0100
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     Harald Freudenberger <freude@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, borntraeger@...ibm.com, cohuck@...hat.com,
        mjrosato@...ux.ibm.com, alex.williamson@...hat.com,
        kwankhede@...dia.com, fiuczy@...ux.ibm.com, frankja@...ux.ibm.com,
        david@...hat.com, hca@...ux.ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v11 04/14] s390/zcrypt: driver callback to indicate
 resource in use

On Fri, 13 Nov 2020 16:30:31 -0500
Tony Krowiak <akrowiak@...ux.ibm.com> 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.

Regards,
Halil