rcutorture: Use monotonic timestamp for stall detection

The get_seconds() call is deprecated because it overflows on 32-bit
architectures. The algorithm in rcu_torture_stall() can deal with
the overflow, but another problem here is that using a CLOCK_REALTIME
stamp can lead to a false-positive stall warning when a settimeofday()
happens concurrently.

Using ktime_get_seconds() instead avoids those issues and will never
overflow. The added cast to 'unsigned long' however is necessary to
make ULONG_CMP_LT() work correctly.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 36b9b82662131509f0e6e6cf2da4760b548d4cdd..049b3735dba834483d76342f71135ca36489b612 100644 (file)
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1622,7 +1622,7 @@ static int rcu_torture_stall(void *args)
                VERBOSE_TOROUT_STRING("rcu_torture_stall end holdoff");
        }
        if (!kthread_should_stop()) {
-               stop_at = get_seconds() + stall_cpu;
+               stop_at = ktime_get_seconds() + stall_cpu;
                /* RCU CPU stall is expected behavior in following code. */
                rcu_read_lock();
                if (stall_cpu_irqsoff)
@@ -1631,7 +1631,8 @@ static int rcu_torture_stall(void *args)
                        preempt_disable();
                pr_alert("rcu_torture_stall start on CPU %d.\n",
                         smp_processor_id());
-               while (ULONG_CMP_LT(get_seconds(), stop_at))
+               while (ULONG_CMP_LT((unsigned long)ktime_get_seconds(),
+                                   stop_at))
                        continue;  /* Induce RCU CPU stall warning. */
                if (stall_cpu_irqsoff)
                        local_irq_enable();