Re: [Xen-devel] [PATCH 1/2] xenbus: don't bail early from xenbus_dev_request_and_reply()

[David Vrabel <david.vrabel@citrix.com>]

On 07/07/16 14:13, David Vrabel wrote:
> On 07/07/16 13:23, Jan Beulich wrote:
>>>>> On 07.07.16 at 14:17, <david.vrabel@citrix.com> wrote:
>>> On 07/07/16 13:09, Jan Beulich wrote:
>>>>>>> On 07.07.16 at 13:36, <david.vrabel@citrix.com> wrote:
>>>>> On 07/07/16 08:32, Jan Beulich wrote:
>>>>>> We must not skip the transaction_end() call for a failed
>>>>>> XS_TRANSACTION_START. The removed code fragment got introduced by
>>>>>> commit 027bd7e899 ("xen/xenbus: Avoid synchronous wait on XenBus
>>>>>> stalling shutdown/restart") without its description really indicating
>>>>>> why it was added (and hence I can't identify whether a more complex
>>>>>> change might be needed here).
>>>>>
>>>>> If sending the XS_TRANSACTION_END message failed, then the transaction
>>>>> is still open and transaction_end() should not be called.
>>>>>
>>>>> However, if sending an XS_TRANSACTION_START failed, then
>>>>> transaction_end() should be called.
>>>>>
>>>>> So, yes a more complex fix is needed here.
>>>>
>>>> Well, both of the things you name are what happens with the patch
>>>> in place. So if those two conditions are all that needs to be satisfied,
>>>> then no more complex change is needed afaict (and was the behavior
>>>> before the cross referenced commit) - the question really is whether
>>>> that other commit meant to deal with something _beyond_ those two
>>>> things.
>>>
>>> You call transaction_end() if msg->type == XS_TRANSACTION_END, even if
>>> xb_write() returned an error.
>>
>> When xb_write() returns an error, msg->type gets set to XS_ERROR.
> 
> So?
> 
> 	if ((msg->type == XS_TRANSACTION_END) ||
> 	    (...))
> 		transaction_end();
> 
> We don't check msg->type for XS_TRANSACTION_END messages.

Sorry, being stupid.  Yeah, the change is fine but it needs a better
commit message.

David