Re: [PATCH v4] x86/mce: Don't participate in rendezvous process once nmi_shootdown_cpus() was made

From: Xunlei Pang
Date: Fri Mar 03 2017 - 09:30:09 EST


Ping Boris

On 02/23/2017 at 09:36 PM, Xunlei Pang wrote:
> We met an issue for kdump: after kdump kernel boots up,
> and there comes a broadcasted mce in first kernel, the
> other cpus remaining in first kernel will enter the old
> mce handler of first kernel, then timeout and panic due
> to MCE synchronization, finally reset the kdump cpus.
>
> This patch lets cpus stay quiet after nmi_shootdown_cpus(),
> so after kdump boots, cpus remaining in 1st kernel should
> not do anything except clearing MCG_STATUS. This is useful
> for kdump to let vmcore dumping perform as hard as it can.
>
> Previous efforts:
> https://patchwork.kernel.org/patch/6167631/
> https://lists.gt.net/linux/kernel/2146557
>
> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Suggested-by: Borislav Petkov <bp@xxxxxxxxx>
> Signed-off-by: Xunlei Pang <xlpang@xxxxxxxxxx>
> ---
> v1->v2:
> - Using crashing_cpu according to Borislav's suggestion.
>
> v2->v3:
> - Used crashing_cpu in mce.c explicitly, not skip crashing_cpu.
> - Added some comments.
>
> v3->v4:
> - Added more code comments according to Tony's feedback.
>
> arch/x86/include/asm/reboot.h | 1 +
> arch/x86/kernel/cpu/mcheck/mce.c | 17 +++++++++++++++--
> arch/x86/kernel/reboot.c | 5 +++--
> 3 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/reboot.h b/arch/x86/include/asm/reboot.h
> index 2cb1cc2..fc62ba8 100644
> --- a/arch/x86/include/asm/reboot.h
> +++ b/arch/x86/include/asm/reboot.h
> @@ -15,6 +15,7 @@ struct machine_ops {
> };
>
> extern struct machine_ops machine_ops;
> +extern int crashing_cpu;
>
> void native_machine_crash_shutdown(struct pt_regs *regs);
> void native_machine_shutdown(void);
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 8e9725c..b65505f 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -49,6 +49,7 @@
> #include <asm/tlbflush.h>
> #include <asm/mce.h>
> #include <asm/msr.h>
> +#include <asm/reboot.h>
>
> #include "mce-internal.h"
>
> @@ -1127,9 +1128,21 @@ void do_machine_check(struct pt_regs *regs, long error_code)
> * on Intel.
> */
> int lmce = 1;
> + int cpu = smp_processor_id();
>
> - /* If this CPU is offline, just bail out. */
> - if (cpu_is_offline(smp_processor_id())) {
> + /*
> + * Cases to bail out to avoid rendezvous process timeout:
> + * 1)If this CPU is offline.
> + * 2)If crashing_cpu was set, e.g. entering kdump,
> + * we need to skip cpus remaining in 1st kernel.
> + * Note: there is a small window between kexecing
> + * and kdump kernel establishing new mce handler,
> + * if some MCE comes within the window, there is
> + * no valid mce handler due to pgtable changing,
> + * let's just face the fate.
> + */
> + if (cpu_is_offline(cpu) ||
> + (crashing_cpu != -1 && crashing_cpu != cpu)) {
> u64 mcgstatus;
>
> mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index e244c19..92ecf4b 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -749,10 +749,11 @@ void machine_crash_shutdown(struct pt_regs *regs)
> #endif
>
>
> +/* This keeps a track of which one is crashing cpu. */
> +int crashing_cpu = -1;
> +
> #if defined(CONFIG_SMP)
>
> -/* This keeps a track of which one is crashing cpu. */
> -static int crashing_cpu;
> static nmi_shootdown_cb shootdown_callback;
>
> static atomic_t waiting_for_crash_ipi;