linux-kernel - Re: [PATCH v5 3/4] mm/gup: allow FOLL_LONGTERM & FOLL_PCI

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Message-ID: <ZrwyD10ejPxowETN@infradead.org>
Date: Tue, 13 Aug 2024 21:26:55 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Christoph Hellwig <hch@...radead.org>,
	Martin Oliveira <martin.oliveira@...eticom.com>,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Artemy Kovalyov <artemyko@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Leon Romanovsky <leon@...nel.org>,
	Logan Gunthorpe <logang@...tatee.com>,
	Michael Guralnik <michaelgur@...dia.com>,
	Mike Marciniszyn <mike.marciniszyn@...el.com>,
	Shiraz Saleem <shiraz.saleem@...el.com>, Tejun Heo <tj@...nel.org>,
	John Hubbard <jhubbard@...dia.com>,
	Dan Williams <dan.j.williams@...el.com>,
	David Sloan <david.sloan@...eticom.com>
Subject: Re: [PATCH v5 3/4] mm/gup: allow FOLL_LONGTERM & FOLL_PCI_P2PDMA

On Tue, Aug 13, 2024 at 01:05:02PM -0300, Jason Gunthorpe wrote:
> > Where do we block driver unbind with an open resource?  
> 
> I keep seeing it in different subsystems, safe driver unbind is really
> hard. :\ eg I think VFIO has some waits in it

Well, waits for what?  Usuaully an unbind has to wait for something,
but waiting for unbound references is always a bug.  And I can't
think of any sensible subsystem doing this.