linux-kernel - Re: [PATCH] s390/vfio-ap: do not use open locks during VFIO_GROUP_NOTIFY_SET

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Date:   Tue, 6 Jul 2021 09:39:29 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Halil Pasic <pasic@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, pasic@...ux.vnet.ibm.com,
        jjherne@...ux.ibm.com
Subject: Re: [PATCH] s390/vfio-ap: do not use open locks during
 VFIO_GROUP_NOTIFY_SET_KVM notification



On 7/5/21 10:13 AM, Jason Gunthorpe wrote:
> On Thu, Jul 01, 2021 at 10:28:52AM -0400, Tony Krowiak wrote:
>
>>> I think Jason was talking about open coding locks in general.
>> That may be so, but his comments were in support of his
>> statement that the  mutex + wait_queue did not resolve
>> the issue reported vai the lockdep splat because it turned
>> off lockdep.
> Rgiht, if this used to be proper locks and lockdep complained then
> whatever potential deadlock it found is not magically removed by going
> to a wait_queue. It just removes the lockdep annotations that would
> identify the issue early.
>
> This is why people should not open code locks, it completely defeats
> lockdep. That alone is merit enough for this patch.

When you use the phrase "open code locks", to what are you
specifically referring? I am confused by the use of the phrase
"open code" in this context because open coding, at least as
I understand it, has to do with data analysis.

>
> Jason