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Subject: Re: [PATCH v11 04/14] s390/zcrypt: driver callback to indicate
 resource in use
To:     Halil Pasic <pasic@linux.ibm.com>
Cc:     Harald Freudenberger <freude@linux.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
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        david@redhat.com, hca@linux.ibm.com, gor@linux.ibm.com
References: <20201022171209.19494-1-akrowiak@linux.ibm.com>
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 <dcdb9c78-daf8-1f25-f59a-903f0db96ada@linux.ibm.com>
 <20201114010020.381277c2.pasic@linux.ibm.com>
From:   Tony Krowiak <akrowiak@linux.ibm.com>
Message-ID: <1e6387bc-3bc0-f244-17ae-7acc88cd3f1b@linux.ibm.com>
Date:   Mon, 16 Nov 2020 11:23:38 -0500
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On 11/13/20 7:00 PM, Halil Pasic wrote:
> On Fri, 13 Nov 2020 16:30:31 -0500
> Tony Krowiak <akrowiak@linux.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.

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