Re: [PATCH v2] uio/uio_pci_generic: Introduce refcnt on open/release

[Christoph Hellwig]

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.