linux-kernel - Re: [PATCH v6 02/11] driver core: Add dma_cleanup callback in bus

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Date:   Tue, 22 Feb 2022 12:48:39 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     baolu.lu@...ux.intel.com, Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, kvm@...r.kernel.org,
        rafael@...nel.org, David Airlie <airlied@...ux.ie>,
        linux-pci@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Diana Craciun <diana.craciun@....nxp.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Will Deacon <will@...nel.org>,
        Stuart Yoder <stuyoder@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Cornelia Huck <cohuck@...hat.com>,
        linux-kernel@...r.kernel.org, Li Yang <leoyang.li@....com>,
        iommu@...ts.linux-foundation.org,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v6 02/11] driver core: Add dma_cleanup callback in
 bus_type

On 2/22/22 7:48 AM, Jason Gunthorpe wrote:
>> since we should only care about ownership at probe, hotplug, and other
>> places well outside critical fast-paths, I'm not sure we really need to keep
>> track of that anyway - it can always be recalculated by walking the
>> group->devices list,
> It has to be locked against concurrent probe, and there isn't
> currently any locking scheme that can support this. The owner_cnt is
> effectively a new lock for this purpose. It is the same issue we
> talked about with that VFIO patch you showed me.
> 
> So, using the group->device_list would require adding something else
> somewhere - which I think should happen when someone has
> justification for another use of whatever that something else is.

This series was originated from the similar idea by adding some fields
in driver structure and intercepting it in iommu core. We stopped doing
that due to the lack of lock mechanism between iommu and driver core.
It then evolved into what it is today.

Best regards,
baolu