Sven Schnelle <svens@xxxxxxxxxxxxx> writes: > Valentin Schneider <vschneid@xxxxxxxxxx> writes: > >> On 29/04/24 07:54, Sven Schnelle wrote: >>> The current implementation of available_idle_cpu() doesn't test >>> whether a possible cpu is offline. On s390 this dereferences a >>> NULL pointer in arch_vcpu_is_preempted() because lowcore is not >>> allocated for offline cpus. On x86, tracing also shows calls to >>> available_idle_cpu() after a cpu is disabled, but it looks like >>> this isn't causing any (obvious) issue. Nevertheless, add a check >>> and return early if the cpu isn't online. >>> >>> Signed-off-by: Sven Schnelle <svens@xxxxxxxxxxxxx> >> >> >> So most of the uses of that function is in wakeup task placement. >> o find_idlest_cpu() works on the sched_domain spans, so shouldn't > deal with >> offline CPUs. >> o select_idle_sibling() may issue an available_idle_cpu(prev) with > an >> offline previous, which would trigger your issue. >> >> Currently, even if select_idle_sibling() picks an offline CPU, this > will >> get corrected by select_fallback_rq() at the end of >> select_task_rq(). However, it would make sense to realize @prev > isn't a >> suitable pick before making it to the fallback machinery, in which > case >> your patch makes sense beyond just fixing s390. >> >> Reviewed-by: Valentin Schneider <vschneid@xxxxxxxxxx> > > Thanks for the review! Ingo/Peter, gentle ping, are you planning to > take > this patch? Ping? Thanks, Sven
