Re: [PATCH 2/3] hv: vmbus_post_msg: retry the hypercall on HV_STATUS_INVALID_CONNECTION_ID

[Vitaly Kuznetsov]

Dexuan Cui <decui@xxxxxxxxxxxxx> writes:

>> -----Original Message-----
>> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx]
>> Sent: Thursday, January 29, 2015 21:31 PM
>> To: Dexuan Cui
>> Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; driverdev-
>> devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx;
>> jasowang@xxxxxxxxxx; KY Srinivasan; Haiyang Zhang
>> Subject: Re: [PATCH 2/3] hv: vmbus_post_msg: retry the hypercall on
>> HV_STATUS_INVALID_CONNECTION_ID
>> 
>> Dexuan Cui <decui@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
>> > Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
>> > ---
>> >  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'?
> It looks we only need to care about these error codes here.
>
> BTW, you can get all the hypercall error codes in the top level functional spec:
> http://blogs.msdn.com/b/virtual_pc_guy/archive/2014/02/17/updated-hypervisor-top-level-functional-specification.aspx
> For this hypercall (0x005c), see "14.9.7 HvPostMessage".

Thanks, interesting!

Btw, HV_STATUS_INSUFFICIENT_MEMORY looks suspicious, looks like we can
hit it as well...

I suggest we split all failures here in 2 classes:
1) permanent
2) worth retrying

and treat them accordingly (no big changes, just maybe group them within
hv_post_message() together as it is the only place where these codes are
being used).

>
>> >
>> >  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.
> Thanks for the suggestion!
>
> I think it would be better to add this to the case
> HV_STATUS_INVALID_CONNECTION_ID:
>  ret = -EAGAIN;
> ?

Yes, like fallthrough

>
>> >  		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
> In my experiments, in the HV_STATUS_INVALID_CONNECTION_ID case,
> waiting 100ms is not enough sometimes, so I'd like to wait more time.
> I agree with you both cases can wait 1000ms. I'll update my patch.
>
> BTW, the " case -ENOMEM:" is not reachable(the hypervisor itself doesn't 
> return -ENOMEM), I think. I can remove it.

hv_post_message() can return -EMSGSIZE or do_hypercall() return value
(which becomes u16 in hv_post_message()). So yes, I agree, -ENOMEM is
not possible.

>
> Thanks,
> -- Dexuan

-- 
  Vitaly
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