linux-kernel - [PATCH 1/2] x86/apic: shutdown local APIC before I/O APIC during crash

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Date:	Wed, 29 Jun 2016 12:51:49 +0800
From:	Wei Jiangang <weijg.fnst@...fujitsu.com>
To:	<linux-kernel@...r.kernel.org>
CC:	<tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
	<x86@...nel.org>, <fenghua.yu@...el.com>,
	Wei Jiangang <weijg.fnst@...fujitsu.com>
Subject: [PATCH 1/2] x86/apic: shutdown local APIC before I/O APIC during crash

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'.

However, the former introduced a bug for crashdown.
If specify 'notsc' for capture-kernel, and then trigger crashdown.
The capture-kernel will be blocked at calibrate_delay_converge().

/* wait for "start of" clock tick */
ticks = jiffies;
while (ticks == jiffies)
    ; /* nothing */

serial console log as following,
............
[    0.000000] Linux version 4.7.0-rc2+ (root@...alhost.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...

The bug remains and unsolved for a long time, since 2013.
I find the arch-criminal by bisect.

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>.

Signed-off-by: Wei Jiangang <weijg.fnst@...fujitsu.com>
---
 arch/x86/kernel/crash.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9ef978d69c22..9aa0235c1f7d 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -179,12 +179,13 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 	 */
 	cpu_emergency_stop_pt();

+	lapic_shutdown();
 #ifdef CONFIG_X86_IO_APIC
 	/* Prevent crash_kexec() from deadlocking on ioapic_lock. */
 	ioapic_zap_locks();
 	disable_IO_APIC();
 #endif
-	lapic_shutdown();
+
 #ifdef CONFIG_HPET_TIMER
 	hpet_disable();
 #endif
-- 
1.9.3