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Date:   Fri, 3 Mar 2017 17:07:03 +0800
From:   Xunlei Pang <xpang@...hat.com>
To:     Xunlei Pang <xlpang@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        Borislav Petkov <bp@...en8.de>
Cc:     Tony Luck <tony.luck@...el.com>, Ingo Molnar <mingo@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Junichi Nomura <j-nomura@...jp.nec.com>,
        Kiyoshi Ueda <k-ueda@...jp.nec.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH v4] x86/mce: Don't participate in rendezvous process once
 nmi_shootdown_cpus() was made

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@...jp.nec.com>
> Suggested-by: Borislav Petkov <bp@...en8.de>
> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
> ---
> 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;

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