linux-kernel - Re: [PATCH v4 1/1] mm: introduce put_user

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Message-ID: <20190320145901.GA3216@redhat.com>
Date:   Wed, 20 Mar 2019 10:59:02 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     William Kucharski <william.kucharski@...cle.com>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Dave Chinner <david@...morbit.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        john.hubbard@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Benvenuti <benve@...co.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Tom Talpey <tom@...pey.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH v4 1/1] mm: introduce put_user_page*(), placeholder
 versions

On Wed, Mar 20, 2019 at 08:55:17AM -0600, William Kucharski wrote:
> 
> 
> > On Mar 19, 2019, at 10:33 PM, Jerome Glisse <jglisse@...hat.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,
Jérôme