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From: "Jan Beulich" <JBeulich@suse.com>
To: David Vrabel <david.vrabel@citrix.com>
Cc: Juergen Gross <JGross@suse.com>,
	xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] xenbus: don't bail early from xenbus_dev_request_and_reply()
Date: Thu, 07 Jul 2016 07:35:24 -0600	[thread overview]
Message-ID: <577E76BC02000078000FC3ED@prv-mh.provo.novell.com> (raw)
In-Reply-To: <577E5793.5030209@citrix.com>

>>> On 07.07.16 at 15:22, <david.vrabel@citrix.com> wrote:
> 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.

I can certainly omit the part in parentheses. I don't think I should
omit the reference to the original commit having introduced the issue.
And without a more specific hint I also don't know what else may
need changing. I'm sorry, I know I'm not doing very well in writing
commit messages to your liking.

Jan


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  parent reply	other threads:[~2016-07-07 13:35 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-07  7:25 [PATCH 0/2] xenbus: xenbus_dev_request_and_reply() adjustments Jan Beulich
2016-07-07  7:32 ` [PATCH 1/2] xenbus: don't bail early from xenbus_dev_request_and_reply() Jan Beulich
2016-07-07  7:32 ` [PATCH 2/2] xenbus: simplify xenbus_dev_request_and_reply() Jan Beulich
     [not found] ` <577E219402000078000FBDB6@prv-mh.provo.novell.com>
2016-07-07 11:36   ` [PATCH 1/2] xenbus: don't bail early from xenbus_dev_request_and_reply() David Vrabel
     [not found]   ` <577E3ED0.906@citrix.com>
2016-07-07 12:09     ` Jan Beulich
     [not found]     ` <577E629C02000078000FC32F@prv-mh.provo.novell.com>
2016-07-07 12:17       ` David Vrabel
     [not found]       ` <577E4865.1080307@citrix.com>
2016-07-07 12:23         ` Jan Beulich
     [not found]         ` <577E65CB02000078000FC35B@prv-mh.provo.novell.com>
2016-07-07 13:13           ` David Vrabel
     [not found]           ` <577E5565.40302@citrix.com>
2016-07-07 13:22             ` David Vrabel
     [not found]             ` <577E5793.5030209@citrix.com>
2016-07-07 13:35               ` Jan Beulich [this message]
2016-07-08 10:18                 ` David Vrabel
2016-07-08 10:56 ` [PATCH 0/2] xenbus: xenbus_dev_request_and_reply() adjustments David Vrabel

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