Messages in this thread | | | Date | Fri, 1 Jul 2016 12:36:20 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/2] x86/apic: shutdown local APIC before I/O APIC during crash |
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* Wei Jiangang <weijg.fnst@cn.fujitsu.com> wrote:
> commit <522e66464467> disables I/O APIC before shutdown of > the local APIC for both reboot and crash path. > and commit <2885432aaf15> declares that 'it still makes sense to > quiet IO APIC before disabling Local APIC'.
That's not how we refer to commits in changelogs.
> However, the former introduced a bug for crashdown.
What is 'crashdown'? It's not referred to in the kernel source even once.
> If specify 'notsc' for capture-kernel, and then trigger crashdown. > The capture-kernel will be blocked at calibrate_delay_converge().
This is a more readable way of saying the same:
If we specify the 'notsc' boot parameter for the dump-capture kernel, and then trigger a crash-down, then the dump-capture kernel will hang in calibrate_delay_converge():
(Assuming the changelog first explains what a 'crash-down' is.)
> /* wait for "start of" clock tick */ > ticks = jiffies; > while (ticks == jiffies) > ; /* nothing */
Plase align quoted code to the right with at least a single tab.
> serial console log as following,
serial log of the hang is as follows:
> ............ > [ 0.000000] Linux version 4.7.0-rc2+ (root@localhost.localdomain) > (gcc version 4.8.2 20140120 (Red Hat 4.8.2-16) (GCC) ) #2 SMP Wed Jun > 156 > [ 0.000000] Kernel command line: BOOT_IMAGE=/vmlinuz-4.7.0-rc2+ > root=/dev/mapper/centos-root ro rd.lvm.lv=centos/swap > vconsole.font=latarcyrheb-sun16 rd.lvm.lv=centos/root crashkernel=256M > vconsole.keymap=us console=tty0 console=ttyS0,115200n8 LANG=en_US.UTF-8 > irqpoll nr_cpus=1 reset_devices cgroup_disable=memory mce=off numa=off > panic=10 rootflags=nofail acpi_no_memhotplug notsc > ............ > [ 0.000000] tsc: Kernel compiled with CONFIG_X86_TSC, cannot disable > TSC completely > ............ > [ 0.000000] clocksource: hpet: mask: 0xffffffff max_cycles: > 0xffffffff, max_idle_ns: 133484882848 ns > [ 0.000000] tsc: Fast TSC calibration using PIT > [ 0.000000] tsc: Detected 3192.714 MHz processor > [ 0.000000] Calibrating delay loop...
Just quote the last few lines and skip the useless timestamp column. Also, please right-align this too.
> The bug remains and unsolved for a long time, since 2013. > I find the arch-criminal by bisect.
What is an arch-criminal? Did you want to say:
The bug has been introduced in 2013. I found the buggy commit via bisection.
?
> The commit <522e66464467> used to fix erratum AVR31 for "Intel Atom > Processor C2000 Product Family Specification Update". > You can find the doc at http://www.intel.com/content/dam/www/public/us > /en/documents/specification-updates/atom-c2000-family-spec-update.pdf. > > IMO, > It doesn't make sense that change the order of disabling between > I/O APIC and local APIC just for a certain model C2000. > And I couldn't find any related descriptions for Intel 64 and IA-32 Arch. > > so, I want to revert the crash part of commit <522e66464467>.
So why does the crashdump kernel hang in calibrate_delay_converge()?
To me it appears this is a weakness in the crashdump kernel: it is unable to boot if we crash the original host system in a particular hardware state, right?
By reverting this change we'll just paper over the bug and re-introduce the bug that can result in certain CPUs hanging if the IO-APIC sends an APIC message if the lapic is disabled prematurely.
Thanks,
Ingo
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