Messages in this thread | | | Date | Wed, 15 May 2019 08:18:14 -0700 | From | Matthew Wilcox <> | Subject | Re: Recurring warning in page_copy_sane (inside copy_page_to_iter) when running stress tests involving drop_caches |
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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@infradead.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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