On Thursday, January 09, 2014 10:00:53 AM Vivek Goyal wrote: > On Thu, Jan 09, 2014 at 12:00:29AM +0100, Rafael J. Wysocki wrote: > > [..] > > > The system then panics and the kdump/kexec kernel boots. During this boot > > > ACPi is initialized and the kernel (as can be seen above) > > > > Which is a bug. You're not supposed to initialize ACPI twice in a row. > > [CC lkml, kexec mailing list, dave young] > > It is a fresh instance of kernel booting and it is initializing its data > structures fresh. It is *not* re-initializing ACPI in same kernel. I know. The problem is that the BIOS is generally not stateless and it remebers stuff. In particular, there are a few handshakes done during the ACPI initialization and they cannot be repeated without resetting the BIOS to the initial state, which basically means a reboot. That is kind of orthogonal to the problem at hand, though. > > > This patchset resolves the problem by adding a kernel parameter, > > > no_memory_hotplug, to disable ACPI memory hotplug. It can be added by default > > > as a parameter to the kexec/kdump kernel so the kernel boots correctly. > > > > This problem is specific to kexec/kdump, so please don't add *generic* command > > line parameters to address this. > > > > There are other command line options to solve kdump problems. In general > one might want to disable memory hogplug on the fly even if it is compiled > in the kernel. So it can act as a good debugging aid. > > Secondly, it can be specified with memmap=exactmap and mem=X paramters to > make sure no memory is hot added in the system. > > So I can see other usages of this parameter. To me it makes sense to have > a separate command line option to disable memory hotplug feature on the > fly. Well, if there are other uses, then fine. Thanks! -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.
