rcutorture: Occasionally delay readers enough to make RCU force_quiescent_state

rcutorture already delays readers, but never for long enough to
make RCU force a quiescent state.  Add an occasional delay of
50ms.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josht@linux.vnet.ibm.com
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
LKML-Reference: <12524504772607-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 9 insertions, 6 deletions

diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index b33db539a8ad..328a8257c885 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -281,14 +281,17 @@ static int rcu_torture_read_lock(void) __acquires(RCU)
 
 static void rcu_read_delay(struct rcu_random_state *rrsp)
 {
-        long delay;
-        const long longdelay = 200;
+        const unsigned long shortdelay_us = 200;
+        const unsigned long longdelay_ms = 50;
 
-        /* We want there to be long-running readers, but not all the time. */
+        /* We want a short delay sometimes to make a reader delay the grace
+         * period, and we want a long delay occasionally to trigger
+         * force_quiescent_state. */
 
-        delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay);
-        if (!delay)
-                udelay(longdelay);
+        if (!(rcu_random(rrsp) % (nrealreaders * 2000 * longdelay_ms)))
+                mdelay(longdelay_ms);
+        if (!(rcu_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
+                udelay(shortdelay_us);
 }
 
 static void rcu_torture_read_unlock(int idx) __releases(RCU)