[PATCH rcu 12/25] rcu: Add full-sized polling for cond_sync_exp_full()

[Paul E. McKenney]

The cond_synchronize_rcu_expedited() API compresses the combined expedited and
normal grace-period states into a single unsigned long, which conserves
storage, but can miss grace periods in certain cases involving overlapping
normal and expedited grace periods.  Missing the occasional grace period
is usually not a problem, but there are use cases that care about each
and every grace period.

This commit therefore adds yet another member of the full-state RCU
grace-period polling API, which is the cond_synchronize_rcu_exp_full()
function.  This uses up to three times the storage (rcu_gp_oldstate
structure instead of unsigned long), but is guaranteed not to miss
grace periods.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 include/linux/rcutiny.h |  5 +++
 include/linux/rcutree.h |  1 +
 kernel/rcu/rcutorture.c | 72 ++++++++++++++++++++++++++++-------------
 kernel/rcu/tree_exp.h   | 27 ++++++++++++++++
 4 files changed, 83 insertions(+), 22 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 3bee97f76bf43..4405e9112cee8 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -64,6 +64,11 @@ static inline void cond_synchronize_rcu_expedited(unsigned long oldstate)
 	cond_synchronize_rcu(oldstate);
 }
 
+static inline void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
+{
+	cond_synchronize_rcu_expedited(rgosp->rgos_norm);
+}
+
 extern void rcu_barrier(void);
 
 static inline void synchronize_rcu_expedited(void)
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 1b44288c027da..755b082f4ec62 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -50,6 +50,7 @@ struct rcu_gp_oldstate {
 unsigned long start_poll_synchronize_rcu_expedited(void);
 void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp);
 void cond_synchronize_rcu_expedited(unsigned long oldstate);
+void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp);
 unsigned long get_state_synchronize_rcu(void);
 void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
 unsigned long start_poll_synchronize_rcu(void);
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 9d22161bf7700..8995429c6f1c2 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -85,6 +85,8 @@ torture_param(bool, fwd_progress_need_resched, 1, "Hide cond_resched() behind ne
 torture_param(bool, gp_cond, false, "Use conditional/async GP wait primitives");
 torture_param(bool, gp_cond_exp, false, "Use conditional/async expedited GP wait primitives");
 torture_param(bool, gp_cond_full, false, "Use conditional/async full-state GP wait primitives");
+torture_param(bool, gp_cond_exp_full, false,
+		    "Use conditional/async full-stateexpedited GP wait primitives");
 torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
 torture_param(bool, gp_normal, false, "Use normal (non-expedited) GP wait primitives");
 torture_param(bool, gp_poll, false, "Use polling GP wait primitives");
@@ -199,20 +201,22 @@ static int rcu_torture_writer_state;
 #define RTWS_COND_GET		5
 #define RTWS_COND_GET_FULL	6
 #define RTWS_COND_GET_EXP	7
-#define RTWS_COND_SYNC		8
-#define RTWS_COND_SYNC_FULL	9
-#define RTWS_COND_SYNC_EXP	10
-#define RTWS_POLL_GET		11
-#define RTWS_POLL_GET_FULL	12
-#define RTWS_POLL_GET_EXP	13
-#define RTWS_POLL_GET_EXP_FULL	14
-#define RTWS_POLL_WAIT		15
-#define RTWS_POLL_WAIT_FULL	16
-#define RTWS_POLL_WAIT_EXP	17
-#define RTWS_POLL_WAIT_EXP_FULL	18
-#define RTWS_SYNC		19
-#define RTWS_STUTTER		20
-#define RTWS_STOPPING		21
+#define RTWS_COND_GET_EXP_FULL	8
+#define RTWS_COND_SYNC		9
+#define RTWS_COND_SYNC_FULL	10
+#define RTWS_COND_SYNC_EXP	11
+#define RTWS_COND_SYNC_EXP_FULL	12
+#define RTWS_POLL_GET		13
+#define RTWS_POLL_GET_FULL	14
+#define RTWS_POLL_GET_EXP	15
+#define RTWS_POLL_GET_EXP_FULL	16
+#define RTWS_POLL_WAIT		17
+#define RTWS_POLL_WAIT_FULL	18
+#define RTWS_POLL_WAIT_EXP	19
+#define RTWS_POLL_WAIT_EXP_FULL	20
+#define RTWS_SYNC		21
+#define RTWS_STUTTER		22
+#define RTWS_STOPPING		23
 static const char * const rcu_torture_writer_state_names[] = {
 	"RTWS_FIXED_DELAY",
 	"RTWS_DELAY",
@@ -222,9 +226,11 @@ static const char * const rcu_torture_writer_state_names[] = {
 	"RTWS_COND_GET",
 	"RTWS_COND_GET_FULL",
 	"RTWS_COND_GET_EXP",
+	"RTWS_COND_GET_EXP_FULL",
 	"RTWS_COND_SYNC",
 	"RTWS_COND_SYNC_FULL",
 	"RTWS_COND_SYNC_EXP",
+	"RTWS_COND_SYNC_EXP_FULL",
 	"RTWS_POLL_GET",
 	"RTWS_POLL_GET_FULL",
 	"RTWS_POLL_GET_EXP",
@@ -350,6 +356,7 @@ struct rcu_torture_ops {
 	void (*start_gp_poll_exp_full)(struct rcu_gp_oldstate *rgosp);
 	bool (*poll_gp_state_exp)(unsigned long oldstate);
 	void (*cond_sync_exp)(unsigned long oldstate);
+	void (*cond_sync_exp_full)(struct rcu_gp_oldstate *rgosp);
 	unsigned long (*get_gp_state)(void);
 	void (*get_gp_state_full)(struct rcu_gp_oldstate *rgosp);
 	unsigned long (*get_gp_completed)(void);
@@ -1183,16 +1190,17 @@ static int nsynctypes;
 static void rcu_torture_write_types(void)
 {
 	bool gp_cond1 = gp_cond, gp_cond_exp1 = gp_cond_exp, gp_cond_full1 = gp_cond_full;
-	bool gp_exp1 = gp_exp, gp_poll_exp1 = gp_poll_exp, gp_poll_exp_full1 = gp_poll_exp_full;
-	bool gp_normal1 = gp_normal, gp_poll1 = gp_poll, gp_poll_full1 = gp_poll_full;
-	bool gp_sync1 = gp_sync;
+	bool gp_cond_exp_full1 = gp_cond_exp_full, gp_exp1 = gp_exp, gp_poll_exp1 = gp_poll_exp;
+	bool gp_poll_exp_full1 = gp_poll_exp_full, gp_normal1 = gp_normal, gp_poll1 = gp_poll;
+	bool gp_poll_full1 = gp_poll_full, gp_sync1 = gp_sync;
 
 	/* Initialize synctype[] array.  If none set, take default. */
-	if (!gp_cond1 && !gp_cond_exp1 && !gp_cond_full1 && !gp_exp1 && !gp_poll_exp &&
-	    !gp_poll_exp_full1 && !gp_normal1 && !gp_poll1 && !gp_poll_full1 && !gp_sync1)
-		gp_cond1 = gp_cond_exp1 = gp_cond_full1 = gp_exp1 = gp_poll_exp1 =
-			   gp_poll_exp_full1 = gp_normal1 = gp_poll1 = gp_poll_full1 =
-			   gp_sync1 = true;
+	if (!gp_cond1 && !gp_cond_exp1 && !gp_cond_full1 && !gp_cond_exp_full1 && !gp_exp1 &&
+	    !gp_poll_exp && !gp_poll_exp_full1 && !gp_normal1 && !gp_poll1 && !gp_poll_full1 &&
+	    !gp_sync1)
+		gp_cond1 = gp_cond_exp1 = gp_cond_full1 = gp_cond_exp_full1 = gp_exp1 =
+			   gp_poll_exp1 = gp_poll_exp_full1 = gp_normal1 = gp_poll1 =
+			   gp_poll_full1 = gp_sync1 = true;
 	if (gp_cond1 && cur_ops->get_gp_state && cur_ops->cond_sync) {
 		synctype[nsynctypes++] = RTWS_COND_GET;
 		pr_info("%s: Testing conditional GPs.\n", __func__);
@@ -1211,6 +1219,13 @@ static void rcu_torture_write_types(void)
 	} else if (gp_cond_full && (!cur_ops->get_gp_state || !cur_ops->cond_sync_full)) {
 		pr_alert("%s: gp_cond_full without primitives.\n", __func__);
 	}
+	if (gp_cond_exp_full1 && cur_ops->get_gp_state_exp && cur_ops->cond_sync_exp_full) {
+		synctype[nsynctypes++] = RTWS_COND_GET_EXP_FULL;
+		pr_info("%s: Testing conditional full-state expedited GPs.\n", __func__);
+	} else if (gp_cond_exp_full &&
+		   (!cur_ops->get_gp_state_exp || !cur_ops->cond_sync_exp_full)) {
+		pr_alert("%s: gp_cond_exp_full without primitives.\n", __func__);
+	}
 	if (gp_exp1 && cur_ops->exp_sync) {
 		synctype[nsynctypes++] = RTWS_EXP_SYNC;
 		pr_info("%s: Testing expedited GPs.\n", __func__);
@@ -1418,6 +1433,14 @@ rcu_torture_writer(void *arg)
 				cur_ops->cond_sync_full(&gp_snap_full);
 				rcu_torture_pipe_update(old_rp);
 				break;
+			case RTWS_COND_GET_EXP_FULL:
+				rcu_torture_writer_state = RTWS_COND_GET_EXP_FULL;
+				cur_ops->get_gp_state_full(&gp_snap_full);
+				torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
+				rcu_torture_writer_state = RTWS_COND_SYNC_EXP_FULL;
+				cur_ops->cond_sync_exp_full(&gp_snap_full);
+				rcu_torture_pipe_update(old_rp);
+				break;
 			case RTWS_POLL_GET:
 				rcu_torture_writer_state = RTWS_POLL_GET;
 				gp_snap = cur_ops->start_gp_poll();
@@ -1567,6 +1590,11 @@ rcu_torture_fakewriter(void *arg)
 				torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
 				cur_ops->cond_sync_full(&gp_snap_full);
 				break;
+			case RTWS_COND_GET_EXP_FULL:
+				cur_ops->get_gp_state_full(&gp_snap_full);
+				torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
+				cur_ops->cond_sync_exp_full(&gp_snap_full);
+				break;
 			case RTWS_POLL_GET:
 				gp_snap = cur_ops->start_gp_poll();
 				while (!cur_ops->poll_gp_state(gp_snap)) {
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 18128ee0d36c0..9c0ae834ef076 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -1071,3 +1071,30 @@ void cond_synchronize_rcu_expedited(unsigned long oldstate)
 		synchronize_rcu_expedited();
 }
 EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
+
+/**
+ * cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited RCU grace period
+ * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
+ *
+ * If a full RCU grace period has elapsed since the call to
+ * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
+ * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
+ * obtained, just return.  Otherwise, invoke synchronize_rcu_expedited()
+ * to wait for a full grace period.
+ *
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless.  If the counter wraps, we have waited for
+ * more than 2 billion grace periods (and way more on a 64-bit system!),
+ * so waiting for a couple of additional grace periods should be just fine.
+ *
+ * This function provides the same memory-ordering guarantees that
+ * would be provided by a synchronize_rcu() that was invoked at the call
+ * to the function that provided @rgosp and that returned at the end of
+ * this function.
+ */
+void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
+{
+	if (!poll_state_synchronize_rcu_full(rgosp))
+		synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);
-- 
2.31.1.189.g2e36527f23