[PATCH tip/core/rcu 05/17] rcutorture: Make synctype[] and nsynctype be static global

[paulmck]

From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

Full testing of the new SRCU polling API requires that the fake writers
also use it in order to test concurrent calls to all of the API members,
especially start_poll_synchronize_srcu().  This commit prepares the ground
for this by making the synctype[] and nsynctype variables be static
globals so that the rcu_torture_fakewriter() function can access them.
Initialization of these variables is moved from rcu_torture_writer()
to a new rcu_torture_write_types() function that is invoked from
rcu_torture_init() just before the first writer kthread is spawned.

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 | 62 ++++++++++++++++++++++++++++---------------------
 1 file changed, 36 insertions(+), 26 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 1930d92..ea44a2b 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1062,37 +1062,18 @@ rcu_torture_fqs(void *arg)
 	return 0;
 }
 
+// Used by writers to randomly choose from the available grace-period
+// primitives.  The only purpose of the initialization is to size the array.
+static int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC, RTWS_COND_GET, RTWS_POLL_GET, RTWS_SYNC };
+static int nsynctypes = 0;
+
 /*
- * RCU torture writer kthread.  Repeatedly substitutes a new structure
- * for that pointed to by rcu_torture_current, freeing the old structure
- * after a series of grace periods (the "pipeline").
+ * Determine which grace-period primitives are available.
  */
-static int
-rcu_torture_writer(void *arg)
+static void rcu_torture_write_types(void)
 {
-	bool boot_ended;
-	bool can_expedite = !rcu_gp_is_expedited() && !rcu_gp_is_normal();
-	unsigned long cookie;
-	int expediting = 0;
-	unsigned long gp_snap;
 	bool gp_cond1 = gp_cond, gp_exp1 = gp_exp, gp_normal1 = gp_normal;
 	bool gp_poll1 = gp_poll, gp_sync1 = gp_sync;
-	int i;
-	int idx;
-	int oldnice = task_nice(current);
-	struct rcu_torture *rp;
-	struct rcu_torture *old_rp;
-	static DEFINE_TORTURE_RANDOM(rand);
-	bool stutter_waited;
-	int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC,
-			   RTWS_COND_GET, RTWS_POLL_GET, RTWS_SYNC };
-	int nsynctypes = 0;
-
-	VERBOSE_TOROUT_STRING("rcu_torture_writer task started");
-	if (!can_expedite)
-		pr_alert("%s" TORTURE_FLAG
-			 " GP expediting controlled from boot/sysfs for %s.\n",
-			 torture_type, cur_ops->name);
 
 	/* Initialize synctype[] array.  If none set, take default. */
 	if (!gp_cond1 && !gp_exp1 && !gp_normal1 && !gp_poll1 && !gp_sync1)
@@ -1127,6 +1108,34 @@ rcu_torture_writer(void *arg)
 	} else if (gp_sync && !cur_ops->sync) {
 		pr_alert("%s: gp_sync without primitives.\n", __func__);
 	}
+}
+
+/*
+ * RCU torture writer kthread.  Repeatedly substitutes a new structure
+ * for that pointed to by rcu_torture_current, freeing the old structure
+ * after a series of grace periods (the "pipeline").
+ */
+static int
+rcu_torture_writer(void *arg)
+{
+	bool boot_ended;
+	bool can_expedite = !rcu_gp_is_expedited() && !rcu_gp_is_normal();
+	unsigned long cookie;
+	int expediting = 0;
+	unsigned long gp_snap;
+	int i;
+	int idx;
+	int oldnice = task_nice(current);
+	struct rcu_torture *rp;
+	struct rcu_torture *old_rp;
+	static DEFINE_TORTURE_RANDOM(rand);
+	bool stutter_waited;
+
+	VERBOSE_TOROUT_STRING("rcu_torture_writer task started");
+	if (!can_expedite)
+		pr_alert("%s" TORTURE_FLAG
+			 " GP expediting controlled from boot/sysfs for %s.\n",
+			 torture_type, cur_ops->name);
 	if (WARN_ONCE(nsynctypes == 0,
 		      "rcu_torture_writer: No update-side primitives.\n")) {
 		/*
@@ -2889,6 +2898,7 @@ rcu_torture_init(void)
 
 	/* Start up the kthreads. */
 
+	rcu_torture_write_types();
 	firsterr = torture_create_kthread(rcu_torture_writer, NULL,
 					  writer_task);
 	if (firsterr)
-- 
2.9.5