Hi David, On 17.03.24 09:37, Keqian Zhu via wrote: >> For vCPU being hotplugged, qemu_init_vcpu() is called. In this >> function, we set vcpu state as stopped, and then wait vcpu thread to >> be created. >> >> As the vcpu state is stopped, it will inform us it has been created >> and then wait on halt_cond. After we has realized vcpu object, we will >> resume the vcpu thread. >> >> However, during we wait vcpu thread to be created, the bql is >> unlocked, and other thread is allowed to call resume_all_vcpus(), >> which will resume the un-realized vcpu. >> >> This fixes the issue by filter out un-realized vcpu during >> resume_all_vcpus(). > >Similar question: is there a reproducer? > >How could we currently hotplug a VCPU, and while it is being created, see >pause_all_vcpus()/resume_all_vcpus() getting claled. > I described the reason for this at patch 1.
>If I am not getting this wrong, there seems to be some other mechanism missing >that makes sure that this cannot happen. Dropping the BQL half-way through >creating a VCPU might be the problem. > When we add retry mechanism in pause_all_vcpus(), we can solve this problem. With the sematic unchanged for user, which means: With bql, we can make sure all vcpus are paused after pause_all_vcpus() finish, and all vcpus are resumed after resume_all_vcpus() finish. Thanks, Keqian > > -- Cheers, David / dhildenb
