linux-kernel - Re: [PATCH 2/3] hv: vmbus_post_msg: retry the hypercall on HV_STATUS_INVALID_CONNECTION

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Date:	Thu, 29 Jan 2015 14:30:57 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Dexuan Cui <decui@...rosoft.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	driverdev-devel@...uxdriverproject.org, olaf@...fle.de,
	apw@...onical.com, jasowang@...hat.com, kys@...rosoft.com,
	haiyangz@...rosoft.com
Subject: Re: [PATCH 2/3] hv: vmbus_post_msg: retry the hypercall on HV_STATUS_INVALID_CONNECTION_ID

Dexuan Cui <decui@...rosoft.com> writes:

> I got the hypercall error code on Hyper-V 2008 R2 when keeping running
> "rmmod hv_netvsc; modprobe hv_netvsc; rmmod hv_utils; modprobe hv_utils"
> in a Linux guest.
>
> Without the patch, the driver can occasionally fail to load.
>
> CC: "K. Y. Srinivasan" <kys@...rosoft.com>
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> ---
>  arch/x86/include/uapi/asm/hyperv.h | 1 +
>  drivers/hv/connection.c            | 9 +++++++++
>  2 files changed, 10 insertions(+)
>
> diff --git a/arch/x86/include/uapi/asm/hyperv.h b/arch/x86/include/uapi/asm/hyperv.h
> index 90c458e..b9daffb 100644
> --- a/arch/x86/include/uapi/asm/hyperv.h
> +++ b/arch/x86/include/uapi/asm/hyperv.h
> @@ -225,6 +225,7 @@
>  #define HV_STATUS_INVALID_HYPERCALL_CODE	2
>  #define HV_STATUS_INVALID_HYPERCALL_INPUT	3
>  #define HV_STATUS_INVALID_ALIGNMENT		4
> +#define HV_STATUS_INVALID_CONNECTION_ID		18
>  #define HV_STATUS_INSUFFICIENT_BUFFERS		19

The gap beween 4 and 18 tells me there are other codes here ;-) Are they
all 'permanent failures'?

>
>  typedef struct _HV_REFERENCE_TSC_PAGE {
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index c4acd1c..8bd05f3 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -440,6 +440,15 @@ int vmbus_post_msg(void *buffer, size_t buflen)
>  		ret = hv_post_message(conn_id, 1, buffer, buflen);
>
>  		switch (ret) {
> +		case HV_STATUS_INVALID_CONNECTION_ID:
> +			/*
> +			 * We could get this if we send messages too
> +			 * frequently or the host is under low resource
> +			 * conditions: let's wait 1 more second before
> +			 * retrying the hypercall.
> +			 */
> +			msleep(1000);
> +			break;

In case it is our last try (No. 10) we will return '18' from the
function. I suggest we set ret = -ENOMEM here as well.

>  		case HV_STATUS_INSUFFICIENT_BUFFERS:
>  			ret = -ENOMEM;

Or should we treat these two equally? There is a smaller (100ms) sleep
between tries already, we can consider changing it instead.

>  		case -ENOMEM:

-- 
  Vitaly
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