On 09.04.2018 15:12, Paolo Bonzini wrote: > On 09/04/2018 15:07, David Hildenbrand wrote: >> If we have parallel calls to resume/pause_all_vcpus() we can get >> into trouble because the qemu mutex is temporarily dropped while >> waiting for all threads to stop. This can happen e.g. for s390x, where >> resume/pause_all_vcpus() can be triggered by a VCPU. >
I'm also using it resume/pause_all_vcpus() now in a prototype to temporarily get all VCPUs out of KVM, that's how I noticed that this is shaky :) > Why does s390 need to do pause_all_vcpus()/resume_all_vcpus() instead of > just asking the main thread to do it (similar to qemu_system_reset), is > it because diag 308 must be synchronous? Christian implemented it back than to (quoting from another mail) "I did this to prevent a "still running CPU to restart an already stopped one"." The problem is that another VCPU could just be about to send a SIGP START/RESTART to a VCPU. Without the pause_all_vcpus(), the SIGP could be delayed and executed just after the "soft reset", therefore resulting in more than 1 VCPU running. > > One disadvantage of the current approach is that diag 308 does not obey > -no-reboot. Both calls are used for kdump+kexec. "kdump on s390 uses a load normal reset to bring the system in a defined state by doing a subsystem reset", so like a "soft reboot". I don't think that we want to apply "-no-reboot" here. > > Paolo > -- Thanks, David / dhildenb
