linux-kernel - [PATCH tip/core/rcu 04/47] rcu: Add diagnostic for misaligned rcu

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Message-Id: <1328319922-30828-4-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Fri,  3 Feb 2012 17:44:39 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 04/47] rcu: Add diagnostic for misaligned rcu_head structures

From: "Paul E. McKenney" <paul.mckenney@...aro.org>

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@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 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! */
 	debug_rcu_head_queue(head);
 	head->func = func;
 	head->next = NULL;
-- 
1.7.8

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