linux-kernel - Re: [Xen-devel] [PATCH 1/2] xenbus: don't bail early from xenbus_dev_request_and

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Date:	Thu, 07 Jul 2016 06:23:07 -0600
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"David Vrabel" <david.vrabel@...rix.com>
Cc:	<xen-devel@...ts.xenproject.org>, <boris.ostrovsky@...cle.com>,
	"Juergen Gross" <JGross@...e.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 1/2] xenbus: don't bail early from
 xenbus_dev_request_and_reply()

>>> On 07.07.16 at 14:17, <david.vrabel@...rix.com> wrote:
> On 07/07/16 13:09, Jan Beulich wrote:
>>>>> On 07.07.16 at 13:36, <david.vrabel@...rix.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.

Jan