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Date:   Wed, 20 Mar 2019 10:59:02 -0400
From:   Jerome Glisse <jglisse@redhat.com>
To:     William Kucharski <william.kucharski@oracle.com>
Cc:     John Hubbard <jhubbard@nvidia.com>,
        Dave Chinner <david@fromorbit.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        john.hubbard@gmail.com, Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Benvenuti <benve@cisco.com>,
        Christoph Hellwig <hch@infradead.org>,
        Christopher Lameter <cl@linux.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dennis Dalessandro <dennis.dalessandro@intel.com>,
        Doug Ledford <dledford@redhat.com>,
        Ira Weiny <ira.weiny@intel.com>, Jan Kara <jack@suse.cz>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@kernel.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Mike Marciniszyn <mike.marciniszyn@intel.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Tom Talpey <tom@talpey.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org,
        Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH v4 1/1] mm: introduce put_user_page*(), placeholder
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On Wed, Mar 20, 2019 at 08:55:17AM -0600, William Kucharski wrote:
> 
> 
> > On Mar 19, 2019, at 10:33 PM, Jerome Glisse <jglisse@redhat.com> 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.

Cheers,
J?r?me