Re: [PATCH v2 1/3] userfaultfd: UFFDIO_REMAP: rmap preparation

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On 23.09.23 03:31, Suren Baghdasaryan wrote:
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>

As far as the rmap code is concerned, UFFDIO_REMAP only alters the
page->mapping and page->index. It does it while holding the page
lock. However folio_referenced() is doing rmap walks without taking the
folio lock first, so folio_lock_anon_vma_read() must be updated to
re-check that the folio->mapping didn't change after we obtained the
anon_vma read lock.

I'm curious: why don't we need this for existing users of page_move_anon_rmap()? What's special about UFFDIO_REMAP?


--
Cheers,

David / dhildenb




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