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/[email protected] Fixes: 4bdced5c9 ("sched/rt: Simplify the IPI based RT balancing logic") Cc: [email protected] Reported-by: Daniel Wagner <[email protected]> --- 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; + 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.
