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@linux.vnet.ibm.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 78923a50cdb2..b2fe2a273df2 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);
         }
 }