| Date | Thu, 2 Feb 2012 08:22:35 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu 04/41] rcu: Add diagnostic for misaligned rcu_head structures |
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On Wed, Feb 01, 2012 at 05:00:26PM -0800, Josh Triplett wrote: > On Wed, Feb 01, 2012 at 11:41:22AM -0800, Paul E. McKenney wrote: > > The push for energy efficiency will require that RCU tag rcu_head > > structures to indicate whether or not their invocation is time critical. > > This tagging is best carried out in the bottom bits of the ->next > > pointers in the rcu_head structures. This tagging requires that the > > rcu_head structures be properly aligned, so this commit adds the required > > diagnostics. > > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > > unsigned long flags; > > struct rcu_data *rdp; > > > > + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ > > I wonder if this should go out in one of the wrapper macros, so that the > _ONCE means once per call site?
Certainly past experience introducing lockdep-RCU would argue that way. ;-)
However, my testing thus far (famous last words!) has found no misalignments. So I expect that these will be caught as they are inserted, so one at a time should be fine.
Thanx, Paul
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