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Date:   Thu, 14 Apr 2022 23:47:14 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Yao Hongbo <yaohongbo@linux.alibaba.com>, mst@redhat.com,
        alikernel-developer@linux.alibaba.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] uio/uio_pci_generic: Introduce refcnt on open/release
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On Wed, Apr 13, 2022 at 09:33:17AM +0200, Greg KH wrote:
> On Wed, Apr 13, 2022 at 03:01:42PM +0800, Yao Hongbo wrote:
> > If two userspace programs both open the PCI UIO fd, when one
> > of the program exits uncleanly, the other will cause IO hang
> > due to bus-mastering disabled.
> > 
> > It's a common usage for spdk/dpdk to use UIO. So, introduce refcnt
> > to avoid such problems.
> 
> Why do you have multiple userspace programs opening the same device?
> Shouldn't they coordinate?

Independent of that (very valid) question I think the current code is
just broken.  Either we need to prohbit multiple opens or do this kind
of refcounting.