Re: [PATCH v4 1/1] mm: introduce put_user_page*(), placeholder versions

From: Jerome Glisse
Date: Wed Mar 20 2019 - 10:59:16 EST

On Wed, Mar 20, 2019 at 08:55:17AM -0600, William Kucharski wrote:
> > On Mar 19, 2019, at 10:33 PM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote:
> >
> > So i believe best we could do is send a SIGBUS to the process that has
> > GUPed a range of a file that is being truncated this would match what
> > we do for CPU acces. There is no reason access through GUP should be
> > handled any differently.
> This should be done lazily, as there's no need to send the SIGBUS unless
> the GUPed page is actually accessed post-truncate.

Issue is that unlike CPU access we might not be able to detect device
access and thus it is not something we can do lazily for everyone.