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Date: Tue, 9 Oct 2018 16:20:12 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Jan Kara <jack@...e.cz> Cc: john.hubbard@...il.com, Matthew Wilcox <willy@...radead.org>, Michal Hocko <mhocko@...nel.org>, Christopher Lameter <cl@...ux.com>, Jason Gunthorpe <jgg@...pe.ca>, Dan Williams <dan.j.williams@...el.com>, linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>, linux-rdma <linux-rdma@...r.kernel.org>, linux-fsdevel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>, Al Viro <viro@...iv.linux.org.uk>, Jerome Glisse <jglisse@...hat.com>, Christoph Hellwig <hch@...radead.org>, Ralph Campbell <rcampbell@...dia.com> Subject: Re: [PATCH v4 2/3] mm: introduce put_user_page*(), placeholder versions On Tue, 9 Oct 2018 10:30:25 +0200 Jan Kara <jack@...e.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?
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