linux-kernel - Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user

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Message-ID: <20180618081113.GA16991@lst.de>
Date:   Mon, 18 Jun 2018 10:11:13 +0200
From:   Christoph Hellwig <hch@....de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, john.hubbard@...il.com,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>, Jan Kara <jack@...e.cz>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()

On Sun, Jun 17, 2018 at 01:10:04PM -0700, Dan Williams wrote:
> I believe kernel behavior regression is a primary concern as now
> fallocate() and truncate() can randomly fail where they didn't before.

Fail or block forever due to actions of other unprivileged users.

That is a complete no-go.