Messages in this thread | | | Date | Sun, 11 May 2014 17:06:19 -0700 | From | Kent Overstreet <> | Subject | Re: [PATCH percpu/for-3.16 2/2] percpu-refcount: implement percpu_ref_tryget() |
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On Fri, May 09, 2014 at 03:55:22PM -0400, Tejun Heo wrote: > Hello, > > On Fri, May 09, 2014 at 12:51:09PM -0700, Kent Overstreet wrote: > > Well not so much deprecated as "bad, avoid" - IMO using tryget() almost always > > (I haven't seen a convincing counterexample) means you screwed up your > > refcounting somewhere, if you need to take a ref on something whatever made that > > object visible to you should have its own ref. > > > > (I think we had this debate, but that was awhile ago...) > > Oh sure, tryget can definitely be misunderstood but RCU protected > iteration is one valid use case. > > rcu_read_lock(); > locate the object of interest; > tryget[_live]() depending on the use case; > rcu_read_unlock(); > > access the object.
No, it's not needed with RCU... look at the aio code for an example (or don't, save your eyes instead).
Conceptually the RCU data structure should own a refcount on the things that are accessible via it; that ref shouldn't be dropped until after it's removed and an RCU barrier has happened.
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