rcu: Add diagnostic for misaligned rcu_head structures

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.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 3cf713a..570f753 100644 (file)
--- 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! */
        debug_rcu_head_queue(head);
        head->func = func;
        head->next = NULL;