On 2017-12-01 13:32:22 [-0500], Steven Rostedt wrote: > > Daniel Wagner reported a crash on the beaglebone black. This is a > single CPU architecture, and does not have a functional: > arch_send_call_function_single_ipi() and can crash if that is called. > > As it only has one CPU, it shouldn't be called, but if the kernel is > compiled for SMP, the push/pull RT scheduling logic now calls it for > irq_work if the one CPU is overloaded, it can use that function to call > itself and crash the kernel. > > There's no reason for the push/pull logic to even be called if there's > only one CPU online. Have it bail if it sees that's the case. > > Link: http://lkml.kernel.org/r/8c913cc2-b2e3-8c2e-e503-aff1428f8ff5@xxxxxxxxx > Fixes: 4bdced5c9 ("sched/rt: Simplify the IPI based RT balancing logic") > Cc: stable@xxxxxxxxxxxxxxx > Reported-by: Daniel Wagner <wagi@xxxxxxxxx> > --- > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 4056c19ca3f0..50d2f8179f70 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1784,6 +1784,10 @@ static int push_rt_task(struct rq *rq) > if (!rq->rt.overloaded) > return 0; > > + /* If we are the only CPU, don't bother */ > + if (num_online_cpus() == 1) > + return 0; > + what about a check next to sched_feat(RT_PUSH_IPI)? I don't know if this is a hot path or not (due to bitmap_weight). If it is, then I would suggest something like a jump-label which is enabled if more than one CPU has been enabled on boot. > next_task = pick_next_pushable_task(rq); > if (!next_task) > return 0; > @@ -2038,6 +2042,10 @@ static void pull_rt_task(struct rq *this_rq) > if (likely(!rt_overloaded(this_rq))) > return; > > + /* If we are the only CPU, don't bother */ > + if (num_online_cpus() == 1) > + return; > + > /* > * Match the barrier from rt_set_overloaded; this guarantees that if we > * see overloaded we must also see the rto_mask bit. Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
