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    SubjectRe: [PATCH v2 0/2] signalfd/epoll fixes
    On Fri, Feb 24, 2012 at 11:06 AM, Oleg Nesterov <oleg@redhat.com> wrote:
    >
    > OK. Please see v2.

    Ok, I applied these.

    And then, dammit, I unapplied them again.

    And then I applied them again.

    I'm *really* conflicted, because I have this really strong feeling
    that it's just papering over a symptom, and we damn well shouldn't be
    doing that. I really think that what we really should do is allow
    "poll()" to have a "poll_remove" callback (so each "add_poll_wait()"
    will have a callback when it gets remove).

    Then we could make the poll() functions actually do allocations and
    crap - or at least add refcounts - and the "poll_remove()" ones would
    undo them.

    And then we could rip out all this, and make signalfd just do

    static void poll_remove(struct file *file, struct wait_queue *wq)
    {
    struct sighand *sighand = container_of(wq, struct sighand, signalfd_wqh);
    __cleanup_sighand(sighand);
    }

    and add that "poll_remove" to its file handler operations. And in
    "poll()", it would just do

    atomic_inc(&sighand->count);

    as it does the poll_wait() thing. Sure, we need to have some way to
    test "did we really add it", and only increment the count if so (so
    poll_wait() would need to return a value), but this seems to be the
    *real* fix. Because the real problem is that we cannot currently
    refcount the poll users.

    Ok, so it's just a strong feeling, and I *did* end up applying these
    two patches after all, but I really wonder how hard it would be to
    just add a single new callback function and be able to refcount that
    sighand structure itself.

    Linus


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