On Wed, Jun 24, 2015 at 03:52:48PM +0900, Masami Hiramatsu wrote: > Hi, > > On 2015/06/23 23:05, dwalker@xxxxxxxxxx wrote: > > > > Hi, > > > > There was a commit in kernel/panic.c which altered when the kexec crash kernel is executed, > > > > commit f06e5153f4ae2e2f3b0300f0e260e40cb7fefd45 > > Author: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx> > > Date: Fri Jun 6 14:37:07 2014 -0700 > > > > kernel/panic.c: add "crash_kexec_post_notifiers" option for kdump after panic_notifers > > > > > > This made it possible for smp_send_stop() to be executed prior to calling the kexec crash > > kernel. > > > > The issue is that smp_send_stop() offlines the cores, and other code depend on the cores being online. > > > > In my case on Octeon here's an example, > > > > panic() > > crash_kexec() > > machine_crash_shutdown() > > octeon_generic_shutdown() > > > > Inside octeon_generic_shutdown() the Octeon watchdog is shutdown for_each_online_cpu(), but since > > most of the cpu's already got offlined in smp_send_stop() it means the watchdog is still alive on > > those cores. This results in a reboot during the crash kernel execution. > > Ah, I see. > > > Another example seem to be in default_machine_crash_shutdown() where crash_kexec_prepare_cpus() depends > > on an IPI for saving the registers on different cores. However, the cpu's are all offlined with > > interrupts disabled so they won't be running those IPI's in this case. > > > > I'm looking for any advice on how this should be fixed, or if it's already fixed. I'm not going to be > > submitting a patch so if anyone wants to submit one feel free to do so. > > Hmm, IMHO, when the cpu goes to offline in appropriate way(smp_send_stop), it should stop > watchdog timer on the offlined cpu too. > Or, you can also register crash handler which stops all watchdogs, but it's a bit tricky. > That doesn't really fix all the issue tho. As I was explaining generic MIPS code depends on the cpu's effectively being online for crash data collection (with an IPI). This issue may effect other architectures also, because smp_send_stop() offlines the cpu on other architectures also. I haven't surveyed the other architectures enough to know what issue could happen from this tho. Is it possible to move the smp_send_stop() below the notifiers ? I'm just throwing out ideas. Daniel
