rcutorture: add random preemption

Add random preemption to help we to torture the preemptable rcu.

srcu_read_delay() also calls rcu_read_delay() for shorter delays.

Added comment to preempt_schedule() call indicating that no quiescent
states happen if preemption is disabled.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 2e2726d790b9..729710273dcb 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -303,6 +303,10 @@ static void rcu_read_delay(struct rcu_random_state *rrsp)
                 mdelay(longdelay_ms);
         if (!(rcu_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
                 udelay(shortdelay_us);
+#ifdef CONFIG_PREEMPT
+        if (!preempt_count() && !(rcu_random(rrsp) % (nrealreaders * 20000)))
+                preempt_schedule();  /* No QS if preempt_disable() in effect */
+#endif
 }
 
 static void rcu_torture_read_unlock(int idx) __releases(RCU)
@@ -536,6 +540,8 @@ static void srcu_read_delay(struct rcu_random_state *rrsp)
         delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay * uspertick);
         if (!delay)
                 schedule_timeout_interruptible(longdelay);
+        else
+                rcu_read_delay(rrsp);
 }
 
 static void srcu_torture_read_unlock(int idx) __releases(&srcu_ctl)