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

[Dexuan Cui]

> -----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".

> >
> >  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;
?

> >  		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.

Thanks,
-- Dexuan
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