Messages in this thread | | | Date | Fri, 9 May 2014 15:55:22 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH percpu/for-3.16 2/2] percpu-refcount: implement percpu_ref_tryget() |
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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.
It's not different from why we use atomic_inc_not_zero() in some places. The only difference is that percpu_ref distinguishes live vs. dying states. It's true that this can be used in pretty stupid ways but I think the comments are pretty clear on that. Do you think we need more warning there?
Thanks.
-- tejun
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