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SubjectRe: [PATCH RFC tip/core/rcu 04/41] rcu: Add diagnostic for misaligned rcu_head structures
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?

- Josh Triplett


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