Re: [PATCH linux 2/2] net sched actions: fix refcount decrement on error

[Cong Wang]

On Fri, Apr 14, 2017 at 2:08 AM, Wolfgang Bumiller
<w.bumiller@xxxxxxxxxxx> wrote:
> Before I do that - trying to wrap my head around the interdependencies
> here better to be thorough - I noticed that tcf_hash_release() can
> return ACT_P_DELETED. The ACT_P_CREATED case means tcf_hash_create()
> was used, in the other case the tc_action's ref & bind count is bumped
> by tcf_hash_check() and then also decremented by tcf_hash_release() if
> it existed, iow. kept at 1, but not always: It does always happen in
> act_police.c but in other files such as act_bpf.c or act_connmark.c if
> eg. bind is set they return without decrementing, so both ref&bind count
> are bumped when they return - the refcount logic isn't easy to follow
> for a newcomer. Now there are two uses of __tcf_hash_release() in
> act_api.c which check for a return value of ACT_P_DELETED, in which case
> they call module_put().


That's the nasty part... IIRC, Jamal has fixed two bugs on action refcnt'ing.
We really need to clean up the code.

> So I'm not sure exactly how the module and tc_action counts are related
> (and I usually like to understand my own patches ;-) ).


Each action holds a refcnt to its module, each filter holds a refcnt to
its bound or referenced (unbound) action.


> Maybe I'm missing something obvious but I'm currently a bit confused as
> to whether the tcf_hash_release() call there is okay, or should have its
> return value checked or should depend on ->init()'s ACT_P_CREATED value
> as well?
>

I think it's the same? If we have ACT_P_CREATED here, tcf_hash_release()
will return ACT_P_DELETED for sure because the newly created action has
refcnt==1?

Thanks.