[tip: core/rcu] rcutorture: Add reader-side tests of polling grace-period API

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     bc480a6354ef2e15c26c3bdbd0db647026e788a7
Gitweb:        https://git.kernel.org/tip/bc480a6354ef2e15c26c3bdbd0db647026e788a7
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Sun, 15 Nov 2020 12:45:57 -08:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 04 Jan 2021 13:53:40 -08:00

rcutorture: Add reader-side tests of polling grace-period API

This commit adds reader-side testing of the polling grace-period API.
This testing verifies that a cookie obtained in an SRCU read-side critical
section does not get a true return from poll_state_synchronize_srcu()
within that same critical section.

Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@xxxxxxxxxxxxxx/
Reported-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/rcutorture.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 78ba95d..96d55f0 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1429,6 +1429,7 @@ rcutorture_loop_extend(int *readstate, struct torture_random_state *trsp,
  */
 static bool rcu_torture_one_read(struct torture_random_state *trsp)
 {
+	unsigned long cookie;
 	int i;
 	unsigned long started;
 	unsigned long completed;
@@ -1444,6 +1445,8 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp)
 	WARN_ON_ONCE(!rcu_is_watching());
 	newstate = rcutorture_extend_mask(readstate, trsp);
 	rcutorture_one_extend(&readstate, newstate, trsp, rtrsp++);
+	if (cur_ops->get_gp_state && cur_ops->poll_gp_state)
+		cookie = cur_ops->get_gp_state();
 	started = cur_ops->get_gp_seq();
 	ts = rcu_trace_clock_local();
 	p = rcu_dereference_check(rcu_torture_current,
@@ -1480,6 +1483,13 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp)
 	}
 	__this_cpu_inc(rcu_torture_batch[completed]);
 	preempt_enable();
+	if (cur_ops->get_gp_state && cur_ops->poll_gp_state)
+		WARN_ONCE(cur_ops->poll_gp_state(cookie),
+			  "%s: Cookie check 3 failed %s(%d) %lu->%lu\n",
+			  __func__,
+			  rcu_torture_writer_state_getname(),
+			  rcu_torture_writer_state,
+			  cookie, cur_ops->get_gp_state());
 	rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
 	WARN_ON_ONCE(readstate & RCUTORTURE_RDR_MASK);
 	// This next splat is expected behavior if leakpointer, especially