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Date:   Thu, 2 Jun 2022 13:30:59 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
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        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Don Dutile <ddutile@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Jakowski Andrzej <andrzej.jakowski@intel.com>,
        Minturn Dave B <dave.b.minturn@intel.com>,
        Jason Ekstrand <jason@jlekstrand.net>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Xiong Jianxin <jianxin.xiong@intel.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Ira Weiny <ira.weiny@intel.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Martin Oliveira <martin.oliveira@eideticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@gmail.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [PATCH v6 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem()
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On Thu, Jun 02, 2022 at 10:16:10AM -0600, Logan Gunthorpe wrote:

> > Just stuff the pages into the mmap, and your driver unprobe will
> > automatically block until all the mmaps are closed - no different than
> > having an open file descriptor or something.
> 
> Oh is that what we want?

Yes, it is the typical case - eg if you have a sysfs file open unbind
hangs indefinitely. Many drivers can't unbind while they have open file
descriptors/etc.

A couple drivers go out of their way to allow unbinding while a live
userspace exists but this can get complicated. Usually there should be
a good reason.

The module will already be refcounted anyhow because the mmap points
to a char file which holds a module reference - meaning a simple rmmod
of the driver shouldn't work already..

Jason