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    SubjectRe: [PATCH 21/21] x86/intel_rdt/mbm: Handle counter overflow
    On Thu, 6 Jul 2017, Shivappa Vikas wrote:
    > On Sun, 2 Jul 2017, Thomas Gleixner wrote:
    > > On Mon, 26 Jun 2017, Vikas Shivappa wrote:
    > > > +static void mbm_update(struct rdt_domain *d, int rmid)
    > > > +{
    > > > + struct rmid_read rr;
    > > > +
    > > > + rr.first = false;
    > > > + rr.d = d;
    > > > +
    > > > + if (is_mbm_total_enabled()) {
    > > > + rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
    > > > + __mon_event_count(rmid, &rr);
    > >
    > > This is broken as it is not protected against a concurrent read from user
    > > space which comes in via a smp function call.
    >
    > The read from user also has the rdtgroup_mutex.

    Which is again, completely non obvious and undocumented in the code.

    Aside of that, are you really serious about serializing the world and
    everything on a single global mutex?

    Thanks,

    tglx

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