Messages in this thread | | | From | Sven Schnelle <> | Subject | Re: [PATCH] sched/core: Test online status in available_idle_cpu() | Date | Thu, 16 May 2024 18:38:06 +0200 |
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Sven Schnelle <svens@linux.ibm.com> writes:
> Valentin Schneider <vschneid@redhat.com> 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@linux.ibm.com> >> >> >> 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@redhat.com> > > Thanks for the review! Ingo/Peter, gentle ping, are you planning to > take > this patch?
Ping?
Thanks,
Sven
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