Messages in this thread | | | Date | Wed, 7 Apr 2010 10:13:42 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference_protected |
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On Wed, Apr 07, 2010 at 06:00:27PM +0100, David Howells wrote: > Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > > The new rcu_access_pointer() primitive is for the case where the pointer > > is be fetch and not dereferenced. This primitive may be used without > > protection, RCU or otherwise, due to the fact that it uses ACCESS_ONCE(). > > ... > > +#define rcu_access_pointer(p, c) \ > > NAK. This shouldn't have the conditional parameter 'c'. Given that 'c' (by > analogy to rcu_dereference_check()) is there to describe the conditions under > which it's permitted to dereference the pointer, why is that relevant here? > What is it you're proving?
In some cases, the value of 'c' will indeed be '1', and in those cases, there needs to be a comment stating why it is OK, similar to those required for smp_mb() and friends.
In other cases, there will be a reference counter or a "not yet fully initialized" flag that can (and should) be tested.
Thanx, Paul
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