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Subject[PATCH tip/core/rcu 04/47] rcu: Add diagnostic for misaligned rcu_head structures
From: "Paul E. McKenney" <>

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

Signed-off-by: Paul E. McKenney <>
Signed-off-by: Paul E. McKenney <>
kernel/rcutree.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

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

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