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    SubjectRe: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland
    In message <84144f020710150447o94b1babo8b6e6a647828465f@mail.gmail.com>, "Pekka Enberg" writes:
    > Hi,
    >
    > On 10/15/07, Erez Zadok <ezk@cs.sunysb.edu> wrote:
    > > Pekka, with a small change to your patch (to handle time-based cache
    > > coherency), your patch worked well and passed all my tests. Thanks.
    > >
    > > So now I wonder if we still need the patch to prevent AOP_WRITEPAGE_ACTIVATE
    > > from being returned to userland. I guess we still need it, b/c even with
    > > your patch, generic_writepages() can return AOP_WRITEPAGE_ACTIVATE back to
    > > the VFS and we need to ensure that doesn't "leak" outside the kernel.
    >
    > I wonder whether _not setting_ BDI_CAP_NO_WRITEBACK implies that
    > ->writepage() will never return AOP_WRITEPAGE_ACTIVATE for
    > !wbc->for_reclaim case which would explain why we haven't hit this bug
    > before. Hugh, Andrew?
    >
    > And btw, I think we need to fix ecryptfs too.

    Yes, ecryptfs needs this fix too (and probably a couple of other mmap fixes
    I've made to unionfs recently -- Mike Halcrow already knows :-)

    Of course, running ecryptfs on top of tmpfs is somewhat odd and uncommon;
    but with unionfs, users use tmpfs as the copyup branch very often.

    > Pekka

    Erez.
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