linux-kernel - RE: [PATCH V4 6/6] x86/Hyper-V: Report crash data in die() when panic_on

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Date:   Tue, 31 Mar 2020 13:51:48 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     "ltykernel@...il.com" <ltykernel@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <liuwe@...rosoft.com>
CC:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        vkuznets <vkuznets@...hat.com>
Subject: RE: [PATCH V4 6/6] x86/Hyper-V: Report crash data in die() when
 panic_on_oops is set

From: Tianyu Lan <Tianyu.Lan@...rosoft.com> Sent: Tuesday, March 31, 2020 12:39 AM
> 
> When oops happens with panic_on_oops unset, the oops
> thread is killed by die() and system continues to run.
> In such case, guest should not report crash register
> data to host since system still runs. Fix it.
> 
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> ---
> Change since v3:
> 	Fix compile error
> ---
>  drivers/hv/vmbus_drv.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 172ceae69abb..4bc02aea2098 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -31,6 +31,7 @@
>  #include <linux/kdebug.h>
>  #include <linux/efi.h>
>  #include <linux/random.h>
> +#include <linux/kernel.h>

Unfortunately, adding the #include doesn't solve the problem.  The error occurs when
CONFIG_HYPERV=m, because panic_on_oops is not exported.  I haven't thought it
through, but hopefully there's a solution where panic_on_oops can be tested in
hyperv_report_panic() or some other Hyper-V specific function that's never in a
module, so that we don't need to export panic_on_oops.

Michael

>  #include <linux/syscore_ops.h>
>  #include <clocksource/hyperv_timer.h>
>  #include "hyperv_vmbus.h"
> @@ -91,7 +92,7 @@ static int hyperv_die_event(struct notifier_block *nb, unsigned long
> val,
>  	 * doing hyperv_report_panic_msg() later with kmsg data, don't do
>  	 * the notification here.
>  	 */
> -	if (hyperv_report_reg())
> +	if (hyperv_report_reg() && panic_on_oops)
>  		hyperv_report_panic(regs, val);
>  	return NOTIFY_DONE;
>  }
> --
> 2.14.5