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    SubjectRe: [PATCH 4/5] x86/mce: Fix all mce notifiers to update the mce->handled bitmask
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    Andy Lutomirski <luto@kernel.org> writes:

    > On Thu, Feb 13, 2020 at 2:19 PM Luck, Tony <tony.luck@intel.com> wrote:
    >>
    >> On Thu, Feb 13, 2020 at 06:03:08PM +0100, Borislav Petkov wrote:
    >> > On Wed, Feb 12, 2020 at 12:46:51PM -0800, Tony Luck wrote:
    >> > > If the handler took any action to log or deal with the error, set
    >> > > a bit int mce->handled so that the default handler on the end of
    >> > > the machine check chain can see what has been done.
    >> > >
    >> > > [!!! What to do about NOTIFY_STOP ... any handler that returns this
    >> > > value short-circuits calling subsequent entries on the chain. In
    >> > > some cases this may be the right thing to do ... but it others we
    >> > > really want to keep calling other functions on the chain]
    >> >
    >> > Yes, we can kill that NOTIFY_STOP thing in the mce code since it is
    >> > nasty.
    >>
    >> Well, there are places where we want to keep NOTIFY_STOP.
    >
    > I very very strongly disagree.

    Ack. The unholy mess of cpu hotplug notifiers and the at least 50 bugs
    which were unearthed by converting them to a comprehensible and
    symmetric state machine have documented the insanity of notifiers
    nicely.

    >> 1) Default case for CEC. We want it to "hide" the corrected error.
    >> That was one of the main goals for CEC. We've discussed cases
    >> where CEC shouldn't hide (when internal threshold exceeded and
    >> it tries to take a page offline ... probably something related to
    >> CMCI storms ... though we didn't really come to any conclusion)
    >
    > Then put this logic in do_machine_check() or in some sensible place
    > that it calls via some ops structure or directly. Don't hide it in
    > some incomprehensible, possibly nondeterministic place in a notifier
    > chain.
    >
    >> 2) Errata. Perhaps a vendor/platform specific function at the head
    >> of the notify chain that weeds out errors that should never have
    >> been reported.
    >
    > No, do this before the notifier chain please.

    Right. The amount of possible handlers is really not huge.

    So having a well defined flow of explicit calls including the handling
    of magic workarounds in a central place makes tons of sense.

    Thanks,

    tglx

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