Re: [PATCH-v2 0/4] target: Eliminate se_port + t10_alua_tg_pt_gp_member

[Nicholas A. Bellinger]

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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