Re: minor GEOM disk API change coming
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On 21.06.2012 20:48, Kenneth D. Merry wrote:
>>> In this case, the GEOM disk class instance has been created by
>>> disk_create(), and the taste of the disk is queued in the GEOM
>>> event queue.
>>> =09
>>> While that event is queued, the da(4) instance goes away. When the
>>> open call comes into the da(4) driver, it dereferences the freed
>>> (but non-NULL) peripheral pointer provided by GEOM, which results
>>> in a panic.
>>
>> I think this situation is very specific for the GEOM_DISK class, and
>> this callback will be less useful for other classes.
>> Does g_cancel_event() cannot help you prevent tasting?
>=20
> Calling g_cancel_event(), for instance from disk_gone(), would not
> completely close the race condition. It can't cancel an event that is
> already in progress, and it is possible for the peripheral to go away w=
hile
> the event is marked in progress but before the taste gets far enough in=
to
> daopen() to acquire a reference to the peripheral.
If i understand correctly your patch, you acquires a reference to the
periph and release it when g_destroy_provider finished. What if you will
queue some custom event from the disk_gone() that will call
cddiskgonecb()? Does it close the race? This event will be executed
after the taste completes.
--=20
WBR, Andrey V. Elsukov
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