linux-kernel - Re: [PATCH 1/2] iommu/s390: Fix IOMMU groups

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Date:   Thu, 27 Apr 2017 23:12:32 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Gerald Schaefer <gerald.schaefer@...ibm.com>
Cc:     Sebastian Ott <sebott@...ux.vnet.ibm.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 1/2] iommu/s390: Fix IOMMU groups

On Thu, Apr 27, 2017 at 08:11:42PM +0200, Gerald Schaefer wrote:
> > +void zpci_destroy_iommu(struct zpci_dev *zdev)
> > +{
> > +	iommu_group_put(zdev->group);
> > +	zdev->group = NULL;
> > +}
> 
> While the rest of this patch doesn't seem to make much of a difference to
> the current behavior, I'm wondering where this extra iommu_group_put()
> comes from. It either was erroneously missing before this patch, or it
> is erroneously introduced by this patch.

This is the way to free an iommu-group. It was missing before probably
because it was unclear whether the add_device function allocated a group
or not. So there was no way to know if it needs to be put again in the
remove_device function.

With this patch the iommu-group is explicitly allocated when the
zpci_dev is created and destroyed again with it.


	Joerg