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    SubjectRe: process 'stuck' at exit.
    On Tue, 10 Dec 2013, Linus Torvalds wrote:

    > On Tue, Dec 10, 2013 at 2:57 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
    > >
    > > But how does the access_ok() move do anything helpful here?
    >
    > Just making it all more obvious.
    >
    > > We really need it for the fastpath !fshared case, but for the fshared
    > > case you actively break working code, because you force a VERIFY_WRITE
    > > check into it. The VERIFY_WRITE is necessary for !fshared, because
    > > there is no way that one thread can map the futex RO and the other RW,
    > > right?
    >
    > Nobody actually uses that argument any more (it goes back to the old
    > i386 "let's manually verify that we have write permissions, because
    > the CPU doesn't do it for us in the trap handling"), and it should
    > probably be removed.

    Fair enough.

    > But you're right that it's at least misleading. I'd love to remove it
    > entirely, because it's not even syntax-checked, and it's confusing.
    > But that would be a humongous patch.

    Well, we should ask Julia for a coccinelle patch to limit the
    wreckage. :)

    Seriously, if that VERIFY_WRITE is completely useless we really want
    to get rid of it.

    > So these days, "access_ok()" literally just checks that the address is
    > in the user address space range. And that would seem to always be
    > appropriate for futexes, so why not just do it in the generic code?

    Agreed, but as long as the VERIFY_WRITE argument is there it needs at
    least a big fat comment :)

    Thanks,

    tglx


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