Re: [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions

Gregory Haskins
2009-06-21T18:39:39Z

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Davide Libenzi wrote:
> On Sat, 20 Jun 2009, Gregory Haskins wrote:
>
>
>> Davide Libenzi wrote:
>>
>>> On Sat, 20 Jun 2009, Davide Libenzi wrote:
>>>
>>>
>>>
>>>> On Sat, 20 Jun 2009, Davide Libenzi wrote:
>>>>
>>>>
>>>>
>>>>> How about the one below?
>>>>>
>>>>>
>>>> Maybe with an interface that can be undone w/out a file* :)
>>>>
>>>>
>>> This is another alternative, based on a low-carb diet of your notifier
>>> patch.
>>>
>>>
>> Ah, I should always check if I have more mail before responding to a now
>> stale patch ;)
>>
>
> Here. I changed the eventfd_pollcb_register() prototype to return the full
> registeration time event mask, instead of the POLLIN explicit check.
> Let's give this one some more thought before I push it to Andrew.
>

This looks great, Davide. I am fairly certain I can now solve the races
and even implement Michael's DEASSIGN feature with this patch in place.
I will actually fire it up tomorrow when I am back in the office and
give it a spin, but I do not spy any more races via visual inspection.

Kind Regards,
-Greg

PS: I was wrong with my previous statement about requiring an embeddable
object (eventfd_notifier for me, eventfd_pollcb for you). I think you
can technically solve this issue minimally by merely locking the POLLHUP
and exposing the kref. However, I think that leads to an more awkward
interface (e.g. we already have eventfd_fget() plus we add a new one
like eventfd_refget(), which might confuse users), so I prefer what you
did here. Just thought I would throw that out there in case you would
prefer to change even fewer lines.

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