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    SubjectRe: [PATCH 2/4] set_restore_sigmask TIF_SIGPENDING
    On Tue, 2008-04-08 at 15:35 +0400, Oleg Nesterov wrote:
    > Why do we need any flag? It looks a bit ugly. Isn't it better to introduce
    > the new magic ERESTART_XXX which means ERESTARTNOHAND + restore-sigmask ?
    > We only need this flag as an implicit parameter to the arch dependent do_signal()
    > which we can't call directly, and thus it must imply TIF_SIGPENDING, and it
    > is not valid after do_signal() (should be cleared). This all looks like
    > ERESTART_ magic, why should we add something else ?
    > See also
    > Of course, probably it is too late to change the implementation even if
    > I am right, the question is: what I am missed?

    Q: When ppoll() is interrupted by a signal, what signal mask should be
    active when the signal handler is active?

    I believe that the signal handler should run with the temporary sigmask
    which was set by ppoll(), and the original sigmask should be restored
    only when the handler completes -- and that's what we achieve with

    So a signal which was originally enabled but is temporarily disabled by
    the mask passed to ppoll() will not be able to interrupt the handler for
    the signal which interrupted ppoll().

    Your version will restore the original signal mask _before_ invoking the
    signal handler which interrupted ppoll() -- which I believe is not the
    intended semantics. And IIRC that was the whole point in implementing
    ppoll() in kernel rather than trying to emulate it in userspace in the
    first place.


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