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    SubjectRe: [rfc][patch] remove racy sync_page?
    On Wed, 31 May 2006, Nick Piggin wrote:
    > Jens Axboe wrote:
    > >
    > > Maybe I'm being dense, but I don't see a problem there. You _should_
    > > call the new mapping sync page if it has been migrated.
    >
    > But can some other thread calling lock_page first find the old mapping,
    > and then run its ->sync_page which finds the new mapping? While it may
    > not matter for anyone in-tree, it does break the API so it would be
    > better to either fix it or rip it out than be silently buggy.

    Splicing a page from one mapping to another is rather worrying/exciting,
    but it does look safely done to me. remove_mapping checks page_count
    while page lock and old mapping->tree_lock are held, and gives up if
    anyone else has an interest in the page. And we already know it's
    unsafe to lock_page without holding a reference to the page, don't we?

    Hugh
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