linux-kernel - Re: [PATCH 1/1] Drivers: hv: vmbus: Fix crash handler reset of Hyper-V synic

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Date:   Thu, 14 Nov 2019 11:04:16 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal\@kernel.org" <sashal@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "linux-hyperv\@vger.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: Re: [PATCH 1/1] Drivers: hv: vmbus: Fix crash handler reset of Hyper-V synic

Michael Kelley <mikelley@...rosoft.com> writes:

> The crash handler calls hv_synic_cleanup() to shutdown the
> Hyper-V synthetic interrupt controller.  But if the CPU
> that calls hv_synic_cleanup() has a VMbus channel interrupt
> assigned to it (which is likely the case in smaller VM sizes),
> hv_synic_cleanup() returns an error and the synthetic
> interrupt controller isn't shutdown.  While the lack of
> being shutdown hasn't caused a known problem, it still
> should be fixed for highest reliability.
>
> So directly call hv_synic_disable_regs() instead of
> hv_synic_cleanup(), which ensures that the synic is always
> shutdown.

Generally, when performing kdump doing as little work as possible is
always preferred and hv_synic_cleanup() does too much: taking mutex,
walking through channel list,... 

Also, hv_synic_cleanup() was calling hv_stimer_cleanup() and we have a
second redundant invocation in hv_crash_handler().

>
> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> ---
>  drivers/hv/vmbus_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 664a415..665920d 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -2305,7 +2305,7 @@ static void hv_crash_handler(struct pt_regs *regs)
>  	vmbus_connection.conn_state = DISCONNECTED;
>  	cpu = smp_processor_id();
>  	hv_stimer_cleanup(cpu);
> -	hv_synic_cleanup(cpu);
> +	hv_synic_disable_regs(cpu);
>  	hyperv_cleanup();
>  };

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly