Hi Matthias,

Matthias Behr wrote:
quoted text
> Hi Greg,
>
> I got a few review comments/questions. Pls see below.
>
> Best Regards,
> Matthias
>
> P.S. I'm a kernel newbie so don't hesitate to tell me if I'm wrong ;-)
>
>  =20
>> +/**
>> + * pi_sink_init - initialize a pi_sink before use
>> + * @sink: a sink context
>> + * @ops: pointer to an pi_sink_ops structure
>> + */
>> +static inline void
>> +pi_sink_init(struct pi_sink *sink, struct pi_sink_ops *ops)
>> +{
>> +	atomic_set(&sink->refs, 0);
>> +	sink->ops =3D ops;
>> +}
>>    =20
>
> Shouldn't ops be tested for 0 here? (ASSERT/BUG_ON/...) (get's derefere=
nced later quite often in the form "if (sink->ops->...)".
quoted text
>  =20

This is a good idea.  I will add this.

quoted text
>  =20
>> +/**
>> + * pi_sink_put - down the reference count, freeing the sink if 0
>> + * @node: the node context
>> + * @flags: optional flags to modify behavior.  Reserved, must be 0.
>> + *
>> + * Returns: none
>> + */
>> +static inline void
>> +pi_sink_put(struct pi_sink *sink, unsigned int flags)
>> +{
>> +	if (atomic_dec_and_test(&sink->refs)) {
>> +		if (sink->ops->free)
>> +			sink->ops->free(sink, flags);
>> +	}
>> +}
>>    =20
>
> Shouldn't the atomic/locked part cover the ...->free(...) as well?

Actually, it already does.  The free can only be called by the last=20
reference dropping the ref-count.


quoted text
>  A pi_get right after the atomic_dec_and_test but before the free() cou=
ld lead to a free() with refs>0?
quoted text
>  =20

A pi_get() after the ref could have already dropped to zero is broken at =

a higher layer.  E.g. the caller of pi_get() has to ensure that there=20
are no races against the reference dropping to begin with.  This is the=20
same as any reference-counted object (for instance, see get_task_struct()=
).

Thanks for the review, Matthias!

Regards,
-Greg