From: Michael Kelley <mikelley@xxxxxxxxxxxxx> Sent: Thursday, March 19, 2020 8:15 AM > > From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> Sent: Thursday, March 19, 2020 7:08 AM > > >> > > >> This patchset fixes some issues in the Hyper-V panic code path. > > >> Patch 1 resolves issue that panic system still responses network > > >> packets. > > >> Patch 2-3 resolves crash enlightenment issues. > > >> Patch 4 is to set crash_kexec_post_notifiers to true for Hyper-V > > >> VM in order to report crash data or kmsg to host before running > > >> kdump kernel. > > > > > > I still see an issue that isn't addressed by these patches. The VMbus > > > driver registers a "die notifier" and a "panic notifier". But die() will > > > eventually call panic() if panic_on_oops is set (which I think it typically > > > is). If the CRASH_NOTIFY_MSG option is *not* enabled, then > > > hyperv_report_panic() could get called by the die notifier, and then > > > again by the panic notifier. > > > > > > Do we even need the "die notifier"? If it was removed, there would > > > not be any notification to Hyper-V via the die() path unless panic_on_oops > > > is set, which I think is actually the correct behavior. I'm not > > > completely clear on what is supposed to happen in general to the > > > Linux kernel if panic_on_oops is not set. Does it try to continue to run? > > > If so, then we should not be notifying Hyper-V if panic_on_oops is not > > > set, and removing the die notifier is the right thing to do. > > > > > > > hyperv_report_panic() has re-enter check inside and so kernel only > > reports crash register data once during die(). > > Ah, yes, you are right. > > > From comment in the > > hyperv_report_panic(), register value reported in die chain is more > > exact than value in panic chain. The register value in die chain is > > passed by die() caller. Register value reported in panic chain > > is collected in the hyperv_panic_event(). > > > > If panic_on_oops is not set, the task should be killed and kernel > > still runs. In this case, we may not trigger crash enlightenment. > > I'm not completely clear on your last statement. It seems like there > is still a problem in that die() will call hyperv_report_panic() even if > panic_on_oops is not set. We will have reported a panic to Hyper-V > even though the VM did not stop running. > > Michael There's one more issue to consider. hv_kmsg_dump() skips calling hyperv_report_panic_msg() if sysctl_record_panic_msg has been cleared by a sysctl command. (This sysctl option gives a customer the ability to increase privacy by not having the VM's dmesg contents sent to Hyper-V.) In this case, the earlier hyperv_report_panic() call should be used. Otherwise, there would not be any notification to Hyper-V about the panic. Michael
