Messages in this thread | | | Date | Thu, 29 Sep 2005 18:16:03 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections |
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On Fri, Sep 30, 2005 at 11:04:04AM +1000, Herbert Xu wrote: > On Thu, Sep 29, 2005 at 05:36:42PM -0700, Paul E. McKenney wrote: > > > > > 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; > > > > How about: > > > > rcu_read_lock(); > > in_dev = dev->ip_ptr; > > if (rcu_dereference(in_dev)) { > > atomic_inc(&in_dev->refcnt); > > } > > rcu_read_unlock(); > > return in_dev; > > With this the barrier will taken even when in_dev is NULL. > > I agree this isn't such a big deal since it only impacts Alpha and then > only when in_dev is NULL. But as we already do the branch anyway to > increment the reference count, we might as well make things a little > better for Alpha.
OK, how about this instead?
rcu_read_lock(); in_dev = dev->ip_ptr; if (in_dev) { atomic_inc(&rcu_dereference(in_dev)->refcnt); } rcu_read_unlock(); return in_dev;
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