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Date: Wed, 15 May 2019 08:18:14 -0700 From: Matthew Wilcox <willy@...radead.org> To: Eric Dumazet <edumazet@...gle.com> Cc: Lech Perczak <l.perczak@...lintechnologies.com>, Al Viro <viro@...iv.linux.org.uk>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Piotr Figiel <p.figiel@...lintechnologies.com>, Krzysztof DrobiĆski <k.drobinski@...lintechnologies.com>, Pawel Lenkow <p.lenkow@...lintechnologies.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: Re: Recurring warning in page_copy_sane (inside copy_page_to_iter) when running stress tests involving drop_caches On Wed, May 15, 2019 at 08:02:17AM -0700, Eric Dumazet wrote: > On Wed, May 15, 2019 at 7:43 AM Matthew Wilcox <willy@...radead.org> wrote: > > You're seeing a race between page_address(page) being called twice. > > Between those two calls, something has caused the page to be removed from > > the page_address_map() list. Eric's patch avoids calling page_address(), > > so apply it and be happy. > > Hmm... wont the kmap_atomic() done later, after page_copy_sane() would > suffer from the race ? > > It seems there is a real bug somewhere to fix. No. page_address() called before the kmap_atomic() will look through the list of mappings and see if that page is mapped somewhere. We unmap lazily, so all it takes to trigger this race is that the page _has_ been mapped before, and its mapping gets torn down during this call. While the page is kmapped, its mapping cannot be torn down.
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