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    SubjectRe: process 'stuck' at exit.
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    On Tue, 2013-12-10 at 14:48 -0800, Linus Torvalds wrote:
    > On Tue, Dec 10, 2013 at 2:42 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
    > >
    > > And yes, I remember that we do not do an extra check for the fshared
    > > case, because get_user_pages_fast() should do it for us already. If
    > > not we are fubared not only in the futex code.
    >
    > Yeah. It turns out we do do the access check indirectly - by looking
    > at the PAGE_USER bit, even if we don't necessarily check the actual
    > limits. So get_user_pages_fast() is fine.
    >
    > > But there is a subtle detail:
    >
    > Yup, see my email from ten minutes ago, we found the same thing. And
    > that would seem to explain the endless loop, and also the timing
    > (since Dave mentions he started doing large-pages lately).
    >
    > So I think the "__get_user_pages_fast(address, 1, !ro, &page)" thing
    > should work.
    >
    > Dave, can you re-create that trinity run and test that patch? I think
    > we've got this, but it might be nice to leave the hung machine up and
    > running until it's verified.. Although I don't really see what else we
    > could need or get out of it, so..

    Would it be possible to limit the options to only pass FUTEX_CMP_REQUEUE
    and a read-only uaddr? That should improve confidence when it doesn't
    fail :-)

    --
    Darren Hart
    Intel Open Source Technology Center
    Yocto Project - Linux Kernel




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