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

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Date:	Thu, 7 Jul 2016 13:17:41 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Jan Beulich <JBeulich@...e.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 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.

David