Messages in this thread | | | Date | Fri, 30 Sep 2005 10:27:19 +1000 | Subject | Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections | From | Herbert Xu <> |
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On Thu, Sep 29, 2005 at 05:23:46PM -0700, Paul E. McKenney wrote: > > Is there any case where __in_dev_get() might be called without > needing to be wrapped with rcu_dereference()? If so, then I > agree (FWIW, given my meagre knowledge of Linux networking).
Yes. All paths that call __in_dev_get() under the rtnl do not need rcu_dereference (or any RCU at all) since the rtnl prevents any ip_ptr modification from occuring.
> However, rcu_dereference() only generates a memory barrier on DEC > Alpha, so there is normally no penalty for using it in the NULL-pointer > case. So, when using rcu_dereference() unconditionally simplifies > the code, it may make sense to "just do it".
Here is what the code would look like:
rcu_read_lock(); in_dev = dev->ip_ptr; if (in_dev) { in_dev = rcu_dereference(in_dev); atomic_inc(&in_dev->refcnt); } rcu_read_unlock(); return in_dev;
Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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