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From: Andrew Morton <akpm@linux-foundation.org>
To: Jan Kara <jack@suse.cz>
Cc: john.hubbard@gmail.com, 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>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org, John Hubbard <jhubbard@nvidia.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Jerome Glisse <jglisse@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Ralph Campbell <rcampbell@nvidia.com>
Subject: Re: [PATCH v4 2/3] mm: introduce put_user_page*(), placeholder versions
Date: Tue, 9 Oct 2018 16:20:12 -0700	[thread overview]
Message-ID: <20181009162012.c662ef0b041993557e150035@linux-foundation.org> (raw)
In-Reply-To: <20181009083025.GE11150@quack2.suse.cz>

On Tue, 9 Oct 2018 10:30:25 +0200 Jan Kara <jack@suse.cz> wrote:

> > Also, maintainability.  What happens if someone now uses put_page() by
> > mistake?  Kernel fails in some mysterious fashion?  How can we prevent
> > this from occurring as code evolves?  Is there a cheap way of detecting
> > this bug at runtime?
> 
> The same will happen as with any other reference counting bug - the special
> user reference will leak. It will be pretty hard to debug I agree. I was
> thinking about whether we could provide some type safety against such bugs
> such as get_user_pages() not returning struct page pointers but rather some
> other special type but it would result in a big amount of additional churn
> as we'd have to propagate this different type e.g. through the IO path so
> that IO completion routines could properly call put_user_pages(). So I'm
> not sure it's really worth it.

I'm not really understanding.  Patch 3/3 changes just one infiniband
driver to use put_user_page().  But the changelogs here imply (to me)
that every user of get_user_pages() needs to be converted to
s/put_page/put_user_page/.

Methinks a bit more explanation is needed in these changelogs?

  reply	other threads:[~2018-10-09 23:20 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-08 21:16 [PATCH v4 0/3] get_user_pages*() and RDMA: first steps john.hubbard
2018-10-08 21:16 ` [PATCH v4 1/3] mm: get_user_pages: consolidate error handling john.hubbard
2018-10-09  0:05   ` Andrew Morton
2018-10-08 21:16 ` [PATCH v4 2/3] mm: introduce put_user_page*(), placeholder versions john.hubbard
2018-10-09  0:14   ` Andrew Morton
2018-10-09  8:30     ` Jan Kara
2018-10-09 23:20       ` Andrew Morton [this message]
2018-10-10  0:32         ` John Hubbard
2018-10-10  0:32           ` John Hubbard
2018-10-10 23:43           ` Andrew Morton
2018-10-10 23:43             ` Andrew Morton
2018-10-10  0:42     ` John Hubbard
2018-10-10  0:42       ` John Hubbard
2018-10-10  8:59       ` Jan Kara
2018-10-10 23:23         ` John Hubbard
2018-10-10 23:23           ` John Hubbard
2018-10-11  8:42           ` Jan Kara
2018-10-10 23:45       ` Andrew Morton
2018-10-10 23:45         ` Andrew Morton
2018-10-11  8:49         ` Jan Kara
2018-10-11 13:20           ` Jason Gunthorpe
2018-10-12  1:23             ` John Hubbard
2018-10-12  1:23               ` John Hubbard
2018-10-12  3:53               ` John Hubbard
2018-10-12  3:53                 ` John Hubbard
2018-10-18 10:19                 ` Jan Kara
2018-11-05  7:25                   ` John Hubbard
2018-11-05  7:25                     ` John Hubbard
2018-10-22 19:43               ` Jason Gunthorpe
2018-11-05  7:17                 ` John Hubbard
2018-11-05  7:17                   ` John Hubbard
2018-11-05  8:37                   ` Jan Kara
2018-10-08 21:16 ` [PATCH v4 3/3] infiniband/mm: convert put_page() to put_user_page*() john.hubbard
2018-10-09  9:52   ` kbuild test robot

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