Messages in this thread | | | Date | Tue, 11 Nov 2008 21:10:45 -0600 (CST) | From | Christoph Lameter <> | Subject | Re: [PATCH 2/4] Add replace_page(), change the mapping of pte from one page into another |
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On Wed, 12 Nov 2008, Andrea Arcangeli wrote:
> So are you checking if there's an unresolved reference only in the > very place I just quoted in the previous email? If answer is yes: what > should prevent get_user_pages from running in parallel from another > thread? get_user_pages will trigger a minor fault and get the elevated > reference just after you read page_count. To you it looks like there > is no o_direct in progress when you proceed to the core of migration > code, but in effect o_direct just started a moment after you read the > page count.
get_user_pages() cannot get to it since the pagetables have already been modified. If get_user_pages runs then the fault handling will occur which will block the thread until migration is complete.
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