linux-kernel - [PATCH tip/core/rcu 1/3] rcu: get rid of signed overflow in check_cpu

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Date:	Sun,  8 May 2011 06:34:08 -0700
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,
	patches@...aro.org, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 1/3] rcu: get rid of signed overflow in check_cpu_stall()

Signed integer overflow is undefined by the C standard, so move
calculations to unsigned.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 78923a5..b2fe2a2 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -581,21 +581,24 @@ static void print_cpu_stall(struct rcu_state *rsp)
 
 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 {
-	long delta;
+	unsigned long j;
+	unsigned long js;
 	struct rcu_node *rnp;
 
 	if (rcu_cpu_stall_suppress)
 		return;
-	delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
+	j = ACCESS_ONCE(jiffies);
+	js = ACCESS_ONCE(rsp->jiffies_stall);
 	rnp = rdp->mynode;
-	if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
+	if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
 
 		/* We haven't checked in, so go dump stack. */
 		print_cpu_stall(rsp);
 
-	} else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
+	} else if (rcu_gp_in_progress(rsp) &&
+		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
 
-		/* They had two time units to dump stack, so complain. */
+		/* They had a few time units to dump stack, so complain. */
 		print_other_cpu_stall(rsp);
 	}
 }
-- 
1.7.3.2

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