Merge branch 'gp.2013.09.25a' into HEAD

gp.2013.09.25a: Topic branch for grace-period updates.

include/trace/events/rcu.h

@@ -39,15 +39,26 @@ TRACE_EVENT(rcu_utilization,
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 
 /*
- * Tracepoint for grace-period events: starting and ending a grace
- * period ("start" and "end", respectively), a CPU noting the start
- * of a new grace period or the end of an old grace period ("cpustart"
- * and "cpuend", respectively), a CPU passing through a quiescent
- * state ("cpuqs"), a CPU coming online or going offline ("cpuonl"
- * and "cpuofl", respectively), a CPU being kicked for being too
- * long in dyntick-idle mode ("kick"), a CPU accelerating its new
- * callbacks to RCU_NEXT_READY_TAIL ("AccReadyCB"), and a CPU
- * accelerating its new callbacks to RCU_WAIT_TAIL ("AccWaitCB").
+ * Tracepoint for grace-period events.  Takes a string identifying the
+ * RCU flavor, the grace-period number, and a string identifying the
+ * grace-period-related event as follows:
+ *
+ *	"AccReadyCB": CPU acclerates new callbacks to RCU_NEXT_READY_TAIL.
+ *	"AccWaitCB": CPU accelerates new callbacks to RCU_WAIT_TAIL.
+ *	"newreq": Request a new grace period.
+ *	"start": Start a grace period.
+ *	"cpustart": CPU first notices a grace-period start.
+ *	"cpuqs": CPU passes through a quiescent state.
+ *	"cpuonl": CPU comes online.
+ *	"cpuofl": CPU goes offline.
+ *	"reqwait": GP kthread sleeps waiting for grace-period request.
+ *	"reqwaitsig": GP kthread awakened by signal from reqwait state.
+ *	"fqswait": GP kthread waiting until time to force quiescent states.
+ *	"fqsstart": GP kthread starts forcing quiescent states.
+ *	"fqsend": GP kthread done forcing quiescent states.
+ *	"fqswaitsig": GP kthread awakened by signal from fqswait state.
+ *	"end": End a grace period.
+ *	"cpuend": CPU first notices a grace-period end.
  */
 TRACE_EVENT(rcu_grace_period,
 
@@ -160,6 +171,46 @@ TRACE_EVENT(rcu_grace_period_init,
 		  __entry->grplo, __entry->grphi, __entry->qsmask)
 );
 
+/*
+ * Tracepoint for RCU no-CBs CPU callback handoffs.  This event is intended
+ * to assist debugging of these handoffs.
+ *
+ * The first argument is the name of the RCU flavor, and the second is
+ * the number of the offloaded CPU are extracted.  The third and final
+ * argument is a string as follows:
+ *
+ *	"WakeEmpty": Wake rcuo kthread, first CB to empty list.
+ *	"WakeOvf": Wake rcuo kthread, CB list is huge.
+ *	"WakeNot": Don't wake rcuo kthread.
+ *	"WakeNotPoll": Don't wake rcuo kthread because it is polling.
+ *	"Poll": Start of new polling cycle for rcu_nocb_poll.
+ *	"Sleep": Sleep waiting for CBs for !rcu_nocb_poll.
+ *	"WokeEmpty": rcuo kthread woke to find empty list.
+ *	"WokeNonEmpty": rcuo kthread woke to find non-empty list.
+ *	"WaitQueue": Enqueue partially done, timed wait for it to complete.
+ *	"WokeQueue": Partial enqueue now complete.
+ */
+TRACE_EVENT(rcu_nocb_wake,
+
+	TP_PROTO(const char *rcuname, int cpu, const char *reason),
+
+	TP_ARGS(rcuname, cpu, reason),
+
+	TP_STRUCT__entry(
+		__field(const char *, rcuname)
+		__field(int, cpu)
+		__field(const char *, reason)
+	),
+
+	TP_fast_assign(
+		__entry->rcuname = rcuname;
+		__entry->cpu = cpu;
+		__entry->reason = reason;
+	),
+
+	TP_printk("%s %d %s", __entry->rcuname, __entry->cpu, __entry->reason)
+);
+
 /*
  * Tracepoint for tasks blocking within preemptible-RCU read-side
  * critical sections.  Track the type of RCU (which one day might
@@ -540,17 +591,17 @@ TRACE_EVENT(rcu_invoke_kfree_callback,
 TRACE_EVENT(rcu_batch_end,
 
 	TP_PROTO(const char *rcuname, int callbacks_invoked,
-		 bool cb, bool nr, bool iit, bool risk),
+		 char cb, char nr, char iit, char risk),
 
 	TP_ARGS(rcuname, callbacks_invoked, cb, nr, iit, risk),
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
 		__field(int, callbacks_invoked)
-		__field(bool, cb)
-		__field(bool, nr)
-		__field(bool, iit)
-		__field(bool, risk)
+		__field(char, cb)
+		__field(char, nr)
+		__field(char, iit)
+		__field(char, risk)
 	),
 
 	TP_fast_assign(
@@ -656,6 +707,7 @@ TRACE_EVENT(rcu_barrier,
 #define trace_rcu_future_grace_period(rcuname, gpnum, completed, c, \
 				      level, grplo, grphi, event) \
 				      do { } while (0)
+#define trace_rcu_nocb_wake(rcuname, cpu, reason) do { } while (0)
 #define trace_rcu_preempt_task(rcuname, pid, gpnum) do { } while (0)
 #define trace_rcu_unlock_preempted_task(rcuname, gpnum, pid) do { } while (0)
 #define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, \

kernel/rcutiny.c

@@ -275,7 +275,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	if (&rcp->rcucblist == rcp->donetail) {
 		RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
 		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
-					      ACCESS_ONCE(rcp->rcucblist),
+					      !!ACCESS_ONCE(rcp->rcucblist),
 					      need_resched(),
 					      is_idle_task(current),
 					      false));

kernel/rcutree.c

@@ -1326,7 +1326,7 @@ static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
 }
 
 /*
- * Initialize a new grace period.
+ * Initialize a new grace period.  Return 0 if no grace period required.
  */
 static int rcu_gp_init(struct rcu_state *rsp)
 {
@@ -1335,10 +1335,18 @@ static int rcu_gp_init(struct rcu_state *rsp)
 
 	rcu_bind_gp_kthread();
 	raw_spin_lock_irq(&rnp->lock);
+	if (rsp->gp_flags == 0) {
+		/* Spurious wakeup, tell caller to go back to sleep.  */
+		raw_spin_unlock_irq(&rnp->lock);
+		return 0;
+	}
 	rsp->gp_flags = 0; /* Clear all flags: New grace period. */
 
-	if (rcu_gp_in_progress(rsp)) {
-		/* Grace period already in progress, don't start another.  */
+	if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
+		/*
+		 * Grace period already in progress, don't start another.
+		 * Not supposed to be able to happen.
+		 */
 		raw_spin_unlock_irq(&rnp->lock);
 		return 0;
 	}
@@ -1481,8 +1489,12 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 	rsp->fqs_state = RCU_GP_IDLE;
 	rdp = this_cpu_ptr(rsp->rda);
 	rcu_advance_cbs(rsp, rnp, rdp);  /* Reduce false positives below. */
-	if (cpu_needs_another_gp(rsp, rdp))
+	if (cpu_needs_another_gp(rsp, rdp)) {
 		rsp->gp_flags = RCU_GP_FLAG_INIT;
+		trace_rcu_grace_period(rsp->name,
+				       ACCESS_ONCE(rsp->gpnum),
+				       TPS("newreq"));
+	}
 	raw_spin_unlock_irq(&rnp->lock);
 }
 
@@ -1492,6 +1504,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 static int __noreturn rcu_gp_kthread(void *arg)
 {
 	int fqs_state;
+	int gf;
 	unsigned long j;
 	int ret;
 	struct rcu_state *rsp = arg;
@@ -1501,14 +1514,19 @@ static int __noreturn rcu_gp_kthread(void *arg)
 
 		/* Handle grace-period start. */
 		for (;;) {
+			trace_rcu_grace_period(rsp->name,
+					       ACCESS_ONCE(rsp->gpnum),
+					       TPS("reqwait"));
 			wait_event_interruptible(rsp->gp_wq,
-						 rsp->gp_flags &
+						 ACCESS_ONCE(rsp->gp_flags) &
 						 RCU_GP_FLAG_INIT);
-			if ((rsp->gp_flags & RCU_GP_FLAG_INIT) &&
-			    rcu_gp_init(rsp))
+			if (rcu_gp_init(rsp))
 				break;
 			cond_resched();
 			flush_signals(current);
+			trace_rcu_grace_period(rsp->name,
+					       ACCESS_ONCE(rsp->gpnum),
+					       TPS("reqwaitsig"));
 		}
 
 		/* Handle quiescent-state forcing. */
@@ -1518,10 +1536,16 @@ static int __noreturn rcu_gp_kthread(void *arg)
 			j = HZ;
 			jiffies_till_first_fqs = HZ;
 		}
+		ret = 0;
 		for (;;) {
-			rsp->jiffies_force_qs = jiffies + j;
+			if (!ret)
+				rsp->jiffies_force_qs = jiffies + j;
+			trace_rcu_grace_period(rsp->name,
+					       ACCESS_ONCE(rsp->gpnum),
+					       TPS("fqswait"));
 			ret = wait_event_interruptible_timeout(rsp->gp_wq,
-					(rsp->gp_flags & RCU_GP_FLAG_FQS) ||
+					((gf = ACCESS_ONCE(rsp->gp_flags)) &
+					 RCU_GP_FLAG_FQS) ||
 					(!ACCESS_ONCE(rnp->qsmask) &&
 					 !rcu_preempt_blocked_readers_cgp(rnp)),
 					j);
@@ -1530,13 +1554,23 @@ static int __noreturn rcu_gp_kthread(void *arg)
 			    !rcu_preempt_blocked_readers_cgp(rnp))
 				break;
 			/* If time for quiescent-state forcing, do it. */
-			if (ret == 0 || (rsp->gp_flags & RCU_GP_FLAG_FQS)) {
+			if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
+			    (gf & RCU_GP_FLAG_FQS)) {
+				trace_rcu_grace_period(rsp->name,
+						       ACCESS_ONCE(rsp->gpnum),
+						       TPS("fqsstart"));
 				fqs_state = rcu_gp_fqs(rsp, fqs_state);
+				trace_rcu_grace_period(rsp->name,
+						       ACCESS_ONCE(rsp->gpnum),
+						       TPS("fqsend"));
 				cond_resched();
 			} else {
 				/* Deal with stray signal. */
 				cond_resched();
 				flush_signals(current);
+				trace_rcu_grace_period(rsp->name,
+						       ACCESS_ONCE(rsp->gpnum),
+						       TPS("fqswaitsig"));
 			}
 			j = jiffies_till_next_fqs;
 			if (j > HZ) {
@@ -1584,6 +1618,8 @@ rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
 		return;
 	}
 	rsp->gp_flags = RCU_GP_FLAG_INIT;
+	trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
+			       TPS("newreq"));
 
 	/*
 	 * We can't do wakeups while holding the rnp->lock, as that

kernel/rcutree_plugin.h

@@ -2113,15 +2113,22 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 
 	/* If we are not being polled and there is a kthread, awaken it ... */
 	t = ACCESS_ONCE(rdp->nocb_kthread);
-	if (rcu_nocb_poll || !t)
+	if (rcu_nocb_poll || !t) {
+		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+				    TPS("WakeNotPoll"));
 		return;
+	}
 	len = atomic_long_read(&rdp->nocb_q_count);
 	if (old_rhpp == &rdp->nocb_head) {
 		wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */
 		rdp->qlen_last_fqs_check = 0;
+		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeEmpty"));
 	} else if (len > rdp->qlen_last_fqs_check + qhimark) {
 		wake_up_process(t); /* ... or if many callbacks queued. */
 		rdp->qlen_last_fqs_check = LONG_MAX / 2;
+		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
+	} else {
+		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
 	}
 	return;
 }
@@ -2145,10 +2152,12 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 	if (__is_kfree_rcu_offset((unsigned long)rhp->func))
 		trace_rcu_kfree_callback(rdp->rsp->name, rhp,
 					 (unsigned long)rhp->func,
-					 rdp->qlen_lazy, rdp->qlen);
+					 -atomic_long_read(&rdp->nocb_q_count_lazy),
+					 -atomic_long_read(&rdp->nocb_q_count));
 	else
 		trace_rcu_callback(rdp->rsp->name, rhp,
-				   rdp->qlen_lazy, rdp->qlen);
+				   -atomic_long_read(&rdp->nocb_q_count_lazy),
+				   -atomic_long_read(&rdp->nocb_q_count));
 	return 1;
 }
 
@@ -2226,6 +2235,7 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
 static int rcu_nocb_kthread(void *arg)
 {
 	int c, cl;
+	bool firsttime = 1;
 	struct rcu_head *list;
 	struct rcu_head *next;
 	struct rcu_head **tail;
@@ -2234,14 +2244,27 @@ static int rcu_nocb_kthread(void *arg)
 	/* Each pass through this loop invokes one batch of callbacks */
 	for (;;) {
 		/* If not polling, wait for next batch of callbacks. */
-		if (!rcu_nocb_poll)
+		if (!rcu_nocb_poll) {
+			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+					    TPS("Sleep"));
 			wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
+		} else if (firsttime) {
+			firsttime = 0;
+			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+					    TPS("Poll"));
+		}
 		list = ACCESS_ONCE(rdp->nocb_head);
 		if (!list) {
+			if (!rcu_nocb_poll)
+				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+						    TPS("WokeEmpty"));
 			schedule_timeout_interruptible(1);
 			flush_signals(current);
 			continue;
 		}
+		firsttime = 1;
+		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+				    TPS("WokeNonEmpty"));
 
 		/*
 		 * Extract queued callbacks, update counts, and wait
@@ -2262,7 +2285,11 @@ static int rcu_nocb_kthread(void *arg)
 			next = list->next;
 			/* Wait for enqueuing to complete, if needed. */
 			while (next == NULL && &list->next != tail) {
+				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+						    TPS("WaitQueue"));
 				schedule_timeout_interruptible(1);
+				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+						    TPS("WokeQueue"));
 				next = list->next;
 			}
 			debug_rcu_head_unqueue(list);