Hello. On Thu, Nov 14, 2019 at 04:03:50PM +0000, Valentin Schneider <valentin.schneider@xxxxxxx> wrote: > Michal, could I nag you for a reviewed-by? I'd feel a bit more confident > with any sort of approval from folks who actually do use cpusets. TL;DR I played with the v5.4-rc6 _without_ this fixup and I conclude it unnecessary (IOW my previous theoretical observation was wrong). The original problem is non-issue with v2 cpuset controller, because effective_cpus are never empty. isolcpus doesn't take out cpuset CPUs, hotplug does. In the case, no online CPU remains in the cpuset, it inherits ancestor's non-empty cpuset. I reproduced the problem with v1 (before your fix). However, in v1 effective == allowed (we're destructive and overwrite allowed on hotunplug) and we already check the emptiness of cpumask_intersects(cp->cpus_allowed, housekeeping_cpumask(HK_FLAG_DOMAIN) few lines higher. I.e. the fixup adds redundant check against the empty sched domain production. Sorry for the noise and HTH, Michal
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