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SubjectRe: [PATCH-v2 0/4] target: Eliminate se_port + t10_alua_tg_pt_gp_member
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On Tue, 2015-05-26 at 14:44 +0200, Bart Van Assche wrote:
> On 05/26/15 08:57, Nicholas A. Bellinger wrote:
> > - Add various rcu_dereference and lockless_dereference RCU notation
>
> Hello Nic,
>
> Feedback from an RCU expert (which I'm not) would be appreciated here.
> But my understanding is that lockless_dereference(p) should be used for
> a pointer p that has *not* been annotated as an RCU pointer. I think in
> the for-next branch of the target repository that this macro is used to
> access RCU-annotated pointers. Is that why sparse complains about how
> lockless_dereference() is used in the target tree ?
>

Was curious about this myself.. Thanks for raising the question!

The intention of lockless_dereference() in both this and preceding
series is for __rcu protected pointers that are accessed outside of
rcu_read_lock() protection, and who's lifetime is controlled by a:

- struct kref
- struct percpu_ref
- struct config_group symlink
- RCU updater path with some manner of mutex or spinlock held

This is supposed to be following Paul's comment in rcupdate.h:

* Similar to rcu_dereference(), but for situations where the pointed-to
* object's lifetime is managed by something other than RCU. That
* "something other" might be reference counting or simple immortality.

Paul, would you be to kind to clarify the intention for us..?

Thank you,

--nab



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