linux-kernel - Re: [PATCH] Drivers: hv: vmbus: handle various crash scenarios

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Date:	Fri, 18 Mar 2016 17:11:50 +0100
From:	Radim Krcmar <rkrcmar@...hat.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Alex Ng <alexng@...rosoft.com>, Cathy Avery <cavery@...hat.com>
Subject: Re: [PATCH] Drivers: hv: vmbus: handle various crash scenarios

2016-03-18 16:53+0100, Vitaly Kuznetsov:
> Radim Krcmar <rkrcmar@...hat.com> writes:
>> 2016-03-18 13:33+0100, Vitaly Kuznetsov:
>>> @@ -530,9 +542,17 @@ static void vmbus_wait_for_unload(void)
>>
>> (I'm not a huge fan of the unloaded variable; what about remembering the
>>  header/msgtype here ...
>>
>>>  			unloaded = true;
>>>  
>>>  		vmbus_signal_eom(msg);
>>
>>  and checking its value here?)
>>
> 
> Sure, but we'll have to use a variable for that ... why would it be
> better than 'unloaded'?

It's easier to understand IMO,

  x = mem       |  x = mem
  if *x == sth  |  z = *x
    u = true    |
  eoi()         |  eoi()
  if u          |  if z == sth
    break       |   break

And you can replace msg with the new variable,

 z = *mem
 eoi()
 if z == sth
   break

>> Can't this be NULL?
> 
> It can't, we allocate it from hv_synic_alloc() (and we don't support cpu
> onlining/offlining on WS2012R2+).

Reviewed-by: Radim Krčmář <rkrcmar@...hat.com>

Thanks.

>>> +		msg = (struct hv_message *)page_addr + VMBUS_MESSAGE_SINT;
>>> +		msg->header.message_type = HVMSG_NONE;
>>>  	}
>>
>> (And, this block belongs to a separate function. ;])
> 
> I thought about moving it to hv_crash_handler() but then I decided to
> leave it here as the need for this fixup is rather an artifact of how we
> recieve the message. But I'm flexible here)

Ok, clearing all VCPUs made me think that it would be generally useful.