Re: [PATCH v4 2/3] mm: introduce put_user_page*(), placeholder versions

From: John Hubbard <jhubbard@nvidia.com>
To: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@ziepe.ca>,
	Andrew Morton <akpm@linux-foundation.org>,
	john.hubbard@gmail.com, Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@kernel.org>,
	Christopher Lameter <cl@linux.com>,
	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, 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: Sun, 4 Nov 2018 23:25:31 -0800	[thread overview]
Message-ID: <4f47f3d4-1b00-e534-309c-7fb044337040@nvidia.com> (raw)
In-Reply-To: <20181018101951.GO23493@quack2.suse.cz>

On 10/18/18 3:19 AM, Jan Kara wrote:
> On Thu 11-10-18 20:53:34, John Hubbard wrote:
>> On 10/11/18 6:23 PM, John Hubbard wrote:
>>> On 10/11/18 6:20 AM, Jason Gunthorpe wrote:
>>>> On Thu, Oct 11, 2018 at 10:49:29AM +0200, Jan Kara wrote:
[...]
> Well, put_page() cannot assert page is not dma-pinned as someone can still
> to get_page(), put_page() on dma-pinned page and that must not barf. But
> put_page() could assert that if the page is pinned, refcount is >=
> pincount. That will detect leaked pin references relatively quickly.
> 

That assertion is definitely a life saver. I've been attempting a combination
of finishing up more call site conversions, and runtime testing, and this
lights up the missing conversions pretty nicely.

As I mentioned in another thread just now, I'll send out an updated RFC this week,
so that people can look through it well before the LPC (next week).

thanks,
-- 
John Hubbard
NVIDIA