From: Christoph Hellwig <hch@infradead.org>
To: john.hubbard@gmail.com
Cc: Matthew Wilcox <willy@infradead.org>,
Michal Hocko <mhocko@kernel.org>,
Christopher Lameter <cl@linux.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
linux-rdma <linux-rdma@vger.kernel.org>,
John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()
Date: Mon, 18 Jun 2018 00:56:50 -0700 [thread overview]
Message-ID: <20180618075650.GA7300@infradead.org> (raw)
In-Reply-To: <20180617012510.20139-3-jhubbard@nvidia.com>
On Sat, Jun 16, 2018 at 06:25:10PM -0700, john.hubbard@gmail.com wrote:
> From: John Hubbard <jhubbard@nvidia.com>
>
> This fixes a few problems that come up when using devices (NICs, GPUs,
> for example) that want to have direct access to a chunk of system (CPU)
> memory, so that they can DMA to/from that memory. Problems [1] come up
> if that memory is backed by persistence storage; for example, an ext4
> file system. I've been working on several customer bugs that are hitting
> this, and this patchset fixes those bugs.
What happens if we do get_user_page from two different threads or even
processes on the same page? As far as I can tell from your patch
the first one finishing the page will clear the bit and then we are
back to no protection.
Note that you can reproduce such a condition trivially using direct
I/O reads or writes.
next prev parent reply other threads:[~2018-06-18 7:57 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-17 1:25 [PATCH 0/2] mm: gup: don't unmap or drop filesystem buffers john.hubbard
2018-06-17 1:25 ` [PATCH 1/2] consolidate get_user_pages error handling john.hubbard
2018-06-17 1:25 ` [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*() john.hubbard
2018-06-17 19:53 ` Dan Williams
2018-06-17 20:04 ` Jason Gunthorpe
2018-06-17 20:10 ` Dan Williams
2018-06-17 20:28 ` John Hubbard
2018-06-18 8:12 ` Christoph Hellwig
2018-06-18 17:50 ` John Hubbard
2018-06-18 17:56 ` Dan Williams
2018-06-18 18:14 ` John Hubbard
2018-06-18 19:21 ` Dan Williams
2018-06-18 19:31 ` Jason Gunthorpe
2018-06-18 20:04 ` Dan Williams
2018-06-18 21:36 ` John Hubbard
2018-06-19 8:29 ` Jan Kara
2018-06-19 9:02 ` Matthew Wilcox
2018-06-19 10:41 ` Jan Kara
2018-06-19 18:11 ` John Hubbard
2018-06-20 1:24 ` Dan Williams
2018-06-20 1:34 ` John Hubbard
2018-06-20 1:57 ` Dan Williams
2018-06-20 2:03 ` John Hubbard
2018-06-20 12:08 ` Jan Kara
2018-06-20 22:55 ` John Hubbard
2018-06-21 16:30 ` Jan Kara
2018-06-25 15:21 ` Jan Kara
2018-06-25 19:03 ` John Hubbard
2018-06-26 7:52 ` Jan Kara
2018-06-26 6:31 ` John Hubbard
2018-06-26 11:48 ` Jan Kara
2018-06-26 13:47 ` Michal Hocko
2018-06-26 16:48 ` Jan Kara
2018-06-27 11:32 ` Michal Hocko
2018-06-27 11:53 ` Jan Kara
2018-06-27 11:59 ` Michal Hocko
2018-06-27 12:42 ` Jan Kara
2018-06-27 14:57 ` Jason Gunthorpe
2018-06-27 17:02 ` Jan Kara
2018-06-28 2:42 ` John Hubbard
2018-06-28 9:17 ` Jan Kara
2018-07-02 5:52 ` Leon Romanovsky
2018-07-02 6:10 ` John Hubbard
2018-07-02 6:34 ` Leon Romanovsky
2018-07-02 6:41 ` John Hubbard
2018-07-02 10:36 ` Michal Hocko
2018-07-02 7:02 ` Jan Kara
2018-07-02 14:48 ` Michal Hocko
2018-07-02 6:58 ` Jan Kara
2018-06-18 8:11 ` Christoph Hellwig
2018-06-19 6:15 ` Leon Romanovsky
2018-06-17 22:19 ` John Hubbard
2018-06-18 7:56 ` Christoph Hellwig [this message]
2018-06-18 17:44 ` John Hubbard
2018-06-17 21:54 ` [PATCH 0/2] mm: gup: don't unmap or drop filesystem buffers Christopher Lameter
2018-06-17 22:23 ` John Hubbard
2018-06-18 8:10 ` Christoph Hellwig
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