On Fri, Feb 17, 2012 at 07:21:52PM -0800, Eric W. Biederman wrote: > Don Zickus <dzickus at redhat.com> writes: > > > On Fri, Feb 17, 2012 at 04:41:01AM -0800, Eric W. Biederman wrote: > >> > >> The fix with a guarantee of no more scope creep is to just disable the > >> nmi watchdog on the kexec on panic path. > >> > >> Don if you have time please figure out is needed to ignore nmi's and > >> possible record and/or report them while we boot, otherwise please cook > >> up a patch that just disables the nmi watchdog wherever we are sending > >> it from (the local apic or the ioapic). > > > > Can I keep things even simpler? The original problem was the deadlock > > with the ioapic lock. We fixed that by removing the call to > > disable_IO_APIC(). Can we just leave the disable_local_APIC calls in > > there for now? Is there any real harm? > > > All this rewrite is going to take time which will delay fixing a current > > problem with kexec on panic, the ioapic deadlock. > > Hmm. > > My apologies I just realized that we can not disable the nmi watchdog > safely in all cases. To avoid the deadlock we fundamentally can not > write to the io_apic, because the locks are the io_apic write path. > The nmi watchdog can be sourced from either the local apics or the > io_apics. To disable the nmi_watchdog we need at least potentially > to write io_apic. I am curious where you see the nmi watchdog being sourced from the ioapic? I thought I removed that code 3 or 4 releases ago. > > So it appears to me that the only reasonable and robust thing we can > do is to ignore nmis in the kexec on panic path. > > So it looks to me that the only path forward at this point is to fix > the other bug where an unexpected nmi will kill the kexec on panic boot. > > I just took a look at the code in /sbin/kexec and that code does not in > fact change the idt except when we switch to 16bit mode, which we > definitely do not do in the kexec on panic case. So it appears that we > don't need to coordinate an /sbin/kexec release with a kernel release to > ignore nmis. > > In fact it looks like we only need to fix the interrupt descriptors > loaded in machine_kexec_64.c and head64.c to ignore nmis. > > At which point we will have fixed two bugs and have a much more reliable > kexec on panic implementation. Ok. I'll talk with Vivek about how the can be implemented. Cheers. Don
