On Mon, Jul 8, 2019 at 3:44 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On Fri, 5 Jul 2019, Pingfan Liu wrote: > > > I hit a bug on an AMD machine, with kexec -l nr_cpus=4 option. nr_cpus option > > is used to speed up kdump process, so it is not a rare case. > > But fundamentally wrong, really. > > The rest of the CPUs are in a half baken state and any broadcast event, > e.g. MCE or a stray IPI, will result in a undiagnosable crash. Very appreciate if you can pay more word on it? I tried to figure out your point, but fail. For "a half baked state", I think you concern about LAPIC state, and I expand this point like the following: For IPI: when capture kernel BSP is up, the rest cpus are still loop inside crash_nmi_callback(), so there is no way to eject new IPI from these cpu. Also we disable_local_APIC(), which effectively prevent the LAPIC from responding to IPI, except NMI/INIT/SIPI, which will not occur in crash case. For MCE, I am not sure whether it can broadcast or not between cpus, but as my understanding, it can not. Then is it a problem? >From another view point, is there any difference between nr_cpus=1 and nr_cpus> 1 in crashing case? If stray IPI raises issue to nr_cpus>1, it does for nr_cpus=1. Thanks, Pingfan
