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    SubjectRe: [PATCH] page->flags corruption fix
    On Wed, 8 Oct 2003, Rik van Riel wrote:
    >
    > Though I suspect it's gotten worse since 2.4.14 or so, where
    > we moved the final lru_cache_del() into __free_pages_ok() and
    > the fact that anonymous pages are on the lru lists.

    I agree both of those make it all more fragile;
    but I still don't quite see where it's broken.

    The existing shortcuts are normally dealing with either a freed
    page or a just allocated, not yet published, page. And you're
    right that the anon->swap case is an exception, less obvious.

    > It's quite possible that one CPU adds the page to the swap
    > cache, while another CPU moves the page around on the inactive
    > list. At that point both CPUs could be fiddling around with
    > the page->flags simultaneously.

    Don't both of those TryLockPage (in one case holding page_table_lock,
    in the other case holding pagemap_lru_lock, to hold the page while
    doing so)?

    > In fact, this has been observed in heavy stress testing by
    > Matt Domsch and Robert Hentosh...

    Perhaps Matt could add description of what they observed, in support
    of the patch. I'm not yet convinced that it's necessarily the fix.

    Hugh

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