rcu: Finish folding ->fqs_state into ->gp_state

Commit commit 4cdfc175c25c89ee ("rcu: Move quiescent-state forcing
into kthread") started the process of folding the old ->fqs_state into
->gp_state, but did not complete it.  This situation does not cause
any malfunction, but can result in extremely confusing trace output.
This commit completes this task of eliminating ->fqs_state in favor
of ->gp_state.

The old ->fqs_state was also used to decide when to collect dyntick-idle
snapshots.  For this purpose, we add a boolean variable into the kthread,
which is set on the first call to rcu_gp_fqs() for a given grace period
and clear otherwise.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

kernel/rcu/tree.c

@@ -98,7 +98,7 @@ struct rcu_state sname##_state = { \
 	.level = { &sname##_state.node[0] }, \
 	.rda = &sname##_data, \
 	.call = cr, \
-	.fqs_state = RCU_GP_IDLE, \
+	.gp_state = RCU_GP_IDLE, \
 	.gpnum = 0UL - 300UL, \
 	.completed = 0UL - 300UL, \
 	.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
@@ -1936,16 +1936,15 @@ static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
 /*
  * Do one round of quiescent-state forcing.
  */
-static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
+static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
 {
-	int fqs_state = fqs_state_in;
 	bool isidle = false;
 	unsigned long maxj;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
 	WRITE_ONCE(rsp->gp_activity, jiffies);
 	rsp->n_force_qs++;
-	if (fqs_state == RCU_SAVE_DYNTICK) {
+	if (first_time) {
 		/* Collect dyntick-idle snapshots. */
 		if (is_sysidle_rcu_state(rsp)) {
 			isidle = true;
@@ -1954,7 +1953,6 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
 		force_qs_rnp(rsp, dyntick_save_progress_counter,
 			     &isidle, &maxj);
 		rcu_sysidle_report_gp(rsp, isidle, maxj);
-		fqs_state = RCU_FORCE_QS;
 	} else {
 		/* Handle dyntick-idle and offline CPUs. */
 		isidle = true;
@@ -1968,7 +1966,6 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
 			   READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
 		raw_spin_unlock_irq(&rnp->lock);
 	}
-	return fqs_state;
 }
 
 /*
@@ -2032,7 +2029,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 	/* Declare grace period done. */
 	WRITE_ONCE(rsp->completed, rsp->gpnum);
 	trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
-	rsp->fqs_state = RCU_GP_IDLE;
+	rsp->gp_state = RCU_GP_IDLE;
 	rdp = this_cpu_ptr(rsp->rda);
 	/* Advance CBs to reduce false positives below. */
 	needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
@@ -2050,7 +2047,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
  */
 static int __noreturn rcu_gp_kthread(void *arg)
 {
-	int fqs_state;
+	bool first_gp_fqs;
 	int gf;
 	unsigned long j;
 	int ret;
@@ -2082,7 +2079,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
 		}
 
 		/* Handle quiescent-state forcing. */
-		fqs_state = RCU_SAVE_DYNTICK;
+		first_gp_fqs = true;
 		j = jiffies_till_first_fqs;
 		if (j > HZ) {
 			j = HZ;
@@ -2110,7 +2107,8 @@ static int __noreturn rcu_gp_kthread(void *arg)
 				trace_rcu_grace_period(rsp->name,
 						       READ_ONCE(rsp->gpnum),
 						       TPS("fqsstart"));
-				fqs_state = rcu_gp_fqs(rsp, fqs_state);
+				rcu_gp_fqs(rsp, first_gp_fqs);
+				first_gp_fqs = false;
 				trace_rcu_grace_period(rsp->name,
 						       READ_ONCE(rsp->gpnum),
 						       TPS("fqsend"));

kernel/rcu/tree.h

@@ -412,13 +412,6 @@ struct rcu_data {
 	struct rcu_state *rsp;
 };
 
-/* Values for fqs_state field in struct rcu_state. */
-#define RCU_GP_IDLE		0	/* No grace period in progress. */
-#define RCU_GP_INIT		1	/* Grace period being initialized. */
-#define RCU_SAVE_DYNTICK	2	/* Need to scan dyntick state. */
-#define RCU_FORCE_QS		3	/* Need to force quiescent state. */
-#define RCU_SIGNAL_INIT		RCU_SAVE_DYNTICK
-
 /* Values for nocb_defer_wakeup field in struct rcu_data. */
 #define RCU_NOGP_WAKE_NOT	0
 #define RCU_NOGP_WAKE		1
@@ -468,9 +461,8 @@ struct rcu_state {
 
 	/* The following fields are guarded by the root rcu_node's lock. */
 
-	u8	fqs_state ____cacheline_internodealigned_in_smp;
-						/* Force QS state. */
-	u8	boost;				/* Subject to priority boost. */
+	u8	boost ____cacheline_internodealigned_in_smp;
+						/* Subject to priority boost. */
 	unsigned long gpnum;			/* Current gp number. */
 	unsigned long completed;		/* # of last completed gp. */
 	struct task_struct *gp_kthread;		/* Task for grace periods. */
@@ -538,7 +530,7 @@ struct rcu_state {
 #define RCU_GP_FLAG_FQS  0x2	/* Need grace-period quiescent-state forcing. */
 
 /* Values for rcu_state structure's gp_flags field. */
-#define RCU_GP_WAIT_INIT 0	/* Initial state. */
+#define RCU_GP_IDLE	 0	/* Initial state and no GP in progress. */
 #define RCU_GP_WAIT_GPS  1	/* Wait for grace-period start. */
 #define RCU_GP_DONE_GPS  2	/* Wait done for grace-period start. */
 #define RCU_GP_WAIT_FQS  3	/* Wait for force-quiescent-state time. */

kernel/rcu/tree_trace.c

@@ -268,7 +268,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 	gpnum = rsp->gpnum;
 	seq_printf(m, "c=%ld g=%ld s=%d jfq=%ld j=%x ",
 		   ulong2long(rsp->completed), ulong2long(gpnum),
-		   rsp->fqs_state,
+		   rsp->gp_state,
 		   (long)(rsp->jiffies_force_qs - jiffies),
 		   (int)(jiffies & 0xffff));
 	seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",