Re: [PATCH for-4.10] libs/evtchn: Remove active handler on clean-up or failure

[Julien Grall <julien.grall@linaro.org>]

Hi Wei,

On 14/11/17 13:53, Wei Liu wrote:
> On Tue, Nov 14, 2017 at 12:14:14PM +0000, Julien Grall wrote:
>> Hi,
>>
>> On 14/11/17 11:51, Ian Jackson wrote:
>>> Ross Lagerwall writes ("Re: [PATCH for-4.10] libs/evtchn: Remove active handler on clean-up or failure"):
>>>> On 11/10/2017 05:10 PM, Julien Grall wrote:
>>>>> Commit 89d55473ed16543044a31d1e0d4660cf5a3f49df "xentoolcore_restrict_all:
>>>>> Implement for libxenevtchn" added a call to register allowing to
>>>>> restrict the event channel.
>>>>>
>>>>> However, the call to deregister the handler was not performed if open
>>>>> failed or when closing the event channel. This will result to corrupt
>>>>> the list of handlers and potentially crash the application later one.
>>>
>>> Sorry for not spotting this during review.
>>> The fix is correct as far as it goes, so:
>>>
>>> Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
>>>
>>>>> The call to xentoolcore_deregister_active_handle is done at the same
>>>>> place as for the grants. But I am not convinced this is thread safe as
>>>>> there are potential race between close the event channel and restict
>>>>> handler. Do we care about that?
>>> ...
>>>> However, I think it should call xentoolcore__deregister_active_handle()
>>>> _before_ calling osdep_evtchn_close() to avoid trying to restrict a
>>>> closed fd or some other fd that happens to have the same number.
>>>
>>> You are right.  But this slightly weakens the guarantee provided by
>>> xentoolcore_restrict_all.
>>>
>>>> I think all the other libs need to be fixed as well, unless there was a
>>>> reason it was done this way.
>>>
>>> I will send a further patch.  In the meantime I suggest we apply
>>> Julien's fix.
>>
>> I am going to leave the decision to you and Wei. It feels a bit odd to
>> release-ack my patch :).
> 
> We can only commit patches that are both acked and release-acked. The
> latter gives RM control over when the patch should be applied.
> Sometimes it is better to wait until something else happens (like
> getting the tree to a stable state).
> 
> That's how I used release-ack anyway.

I feel a bit odd to release-ack my patch and usually for Arm patches 
deferred to Stefano the decision whether the patch is suitable for the 
release.

> 
> For this particular patch, my interpretation of what you just said
> is you've given us release-ack and we can apply this patch anytime. I
> will commit it soon.

Thanks! I hope it will fixed some osstest failure.

Cheers,

-- 
Julien Grall

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