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    SubjectRe: oops if free a locked page

    On Tue, 22 Jun 1999, Andrea Arcangeli wrote:

    > I have a problem with pre-2.3.8-2. It issues an Oops if I attempt to free
    > a locked page. I think I am allowed to free a locked page without first
    > unlock it, because if there's a waiter waiting for the page, the waiter
    > will have just increased the reference count of the page before go to
    > sleep on the page.
    > I want to run try_to_free_buffers() with the page locked and so I want to
    > be allowed to run:
    > /* And free the page */
    > page->buffers = NULL;
    > if (__free_page(page)) {
    > buffermem -= PAGE_SIZE;
    > return 1;
    > }
    > with the page locked. If try_to_free_buffers() will return 1, then I'll
    > avoid the unlock, otherwise I'll do the unlock but after a lot of time
    > (I'll take the page locked just ready for the shrink_mmap-inode path).
    > Right now I removed the BUG() in free-page.

    freeing locked pages is very dangerous. A newly allocated page should be
    unlocked, thats a fair requirement a generic page allocator should have.
    [we have a couple of places that would break in subtle ways if we freed
    locked pages.]

    calling __free_page() with a locked page is fine though - but it must not
    be the 'final' free.

    -- mingo

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