On Fri, Sep 16, 2016 at 08:12:40AM -0700, Andy Lutomirski wrote: > On Fri, Sep 16, 2016 at 12:47 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Thu, Sep 15, 2016 at 02:19:38PM -0500, Josh Poimboeuf wrote: > >> My idea was to use task_rq_lock() to lock the runqueue and then check > >> tsk->on_cpu. I think Peter wasn't too keen on it. > > > > That basically allows a DoS on the scheduler, since a user can run tasks > > on every cpu (through sys_sched_setaffinity()). Then doing while (1) cat > > /proc/$PID/stack would saturate the rq->lock on every CPU. > > > > The more tasks the merrier. > > Is this worse than it would be if this code used preempt_disable() > (which I think it did until very recently)? Much worse, since the proposed task_rq_lock() not only disables preemption, it also disables IRQs and takes 2 locks. And hogging the rq->lock affects other tasks their ability to schedule. -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
