On Fri, Sep 16, 2016 at 8:31 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > 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. > Fair enough. I'm not sure I care quite enough about /proc/PID/stack to personally dig through the scheduler and find a way to cleanly say "please don't run this task for a little while". -- 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
