rcu: Remove RCU CPU stall warnings from Tiny RCU

Tiny RCU's job is to be tiny, so this commit removes its RCU CPU
stall warning code.  After this, there is no longer any need for
rcu_sched_ctrlblk and rcu_bh_ctrlblk to be in tiny_plugin.h, so this
commit also moves them to tiny.c.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/Kconfig

@@ -78,7 +78,7 @@ config TASKS_RCU
 	  user-mode execution as quiescent states.
 
 config RCU_STALL_COMMON
-	def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
+	def_bool ( TREE_RCU || PREEMPT_RCU )
 	help
 	  This option enables RCU CPU stall code that is common between
 	  the TINY and TREE variants of RCU.  The purpose is to allow

kernel/rcu/tiny.c

@@ -38,11 +38,23 @@
 
 #include "rcu.h"
 
-/* Forward declarations for tiny_plugin.h. */
-struct rcu_ctrlblk;
-static void __call_rcu(struct rcu_head *head,
-		       rcu_callback_t func,
-		       struct rcu_ctrlblk *rcp);
+/* Global control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
+	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
+	struct rcu_head **curtail;	/* ->next pointer of last CB. */
+};
+
+/* Definition for rcupdate control block. */
+static struct rcu_ctrlblk rcu_sched_ctrlblk = {
+	.donetail	= &rcu_sched_ctrlblk.rcucblist,
+	.curtail	= &rcu_sched_ctrlblk.rcucblist,
+};
+
+static struct rcu_ctrlblk rcu_bh_ctrlblk = {
+	.donetail	= &rcu_bh_ctrlblk.rcucblist,
+	.curtail	= &rcu_bh_ctrlblk.rcucblist,
+};
 
 #include "tiny_plugin.h"
 
@@ -65,7 +77,6 @@ EXPORT_SYMBOL(rcu_barrier_sched);
  */
 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 {
-	RCU_TRACE(reset_cpu_stall_ticks(rcp);)
 	if (rcp->donetail != rcp->curtail) {
 		rcp->donetail = rcp->curtail;
 		return 1;
@@ -111,7 +122,6 @@ void rcu_bh_qs(void)
  */
 void rcu_check_callbacks(int user)
 {
-	RCU_TRACE(check_cpu_stalls();)
 	if (user)
 		rcu_sched_qs();
 	else if (!in_softirq())
@@ -126,10 +136,8 @@ void rcu_check_callbacks(int user)
  */
 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 {
-	const char *rn = NULL;
 	struct rcu_head *next, *list;
 	unsigned long flags;
-	RCU_TRACE(int cb_count = 0;)
 
 	/* Move the ready-to-invoke callbacks to a local list. */
 	local_irq_save(flags);
@@ -147,18 +155,15 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	local_irq_restore(flags);
 
 	/* Invoke the callbacks on the local list. */
-	RCU_TRACE(rn = rcp->name;)
 	while (list) {
 		next = list->next;
 		prefetch(next);
 		debug_rcu_head_unqueue(list);
 		local_bh_disable();
-		__rcu_reclaim(rn, list);
+		__rcu_reclaim("", list);
 		local_bh_enable();
 		list = next;
-		RCU_TRACE(cb_count++;)
 	}
-	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count);)
 }
 
 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
@@ -202,7 +207,6 @@ static void __call_rcu(struct rcu_head *head,
 	local_irq_save(flags);
 	*rcp->curtail = head;
 	rcp->curtail = &head->next;
-	RCU_TRACE(rcp->qlen++;)
 	local_irq_restore(flags);
 
 	if (unlikely(is_idle_task(current))) {
@@ -235,8 +239,5 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
 void __init rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
-	RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk);)
-	RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk);)
-
 	rcu_early_boot_tests();
 }

kernel/rcu/tiny_plugin.h

@@ -22,34 +22,6 @@
  * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  */
 
-#include <linux/kthread.h>
-#include <linux/init.h>
-
-/* Global control variables for rcupdate callback mechanism. */
-struct rcu_ctrlblk {
-	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
-	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
-	struct rcu_head **curtail;	/* ->next pointer of last CB. */
-	RCU_TRACE(long qlen);		/* Number of pending CBs. */
-	RCU_TRACE(unsigned long gp_start); /* Start time for stalls. */
-	RCU_TRACE(unsigned long ticks_this_gp); /* Statistic for stalls. */
-	RCU_TRACE(unsigned long jiffies_stall); /* Jiffies at next stall. */
-	RCU_TRACE(const char *name);	/* Name of RCU type. */
-};
-
-/* Definition for rcupdate control block. */
-static struct rcu_ctrlblk rcu_sched_ctrlblk = {
-	.donetail	= &rcu_sched_ctrlblk.rcucblist,
-	.curtail	= &rcu_sched_ctrlblk.rcucblist,
-	RCU_TRACE(.name = "rcu_sched")
-};
-
-static struct rcu_ctrlblk rcu_bh_ctrlblk = {
-	.donetail	= &rcu_bh_ctrlblk.rcucblist,
-	.curtail	= &rcu_bh_ctrlblk.rcucblist,
-	RCU_TRACE(.name = "rcu_bh")
-};
-
 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU)
 #include <linux/kernel_stat.h>
 
@@ -73,53 +45,3 @@ void __init rcu_scheduler_starting(void)
 }
 
 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
-
-#ifdef CONFIG_RCU_TRACE
-
-static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	rcp->qlen -= n;
-	local_irq_restore(flags);
-}
-
-static void check_cpu_stall(struct rcu_ctrlblk *rcp)
-{
-	unsigned long j;
-	unsigned long js;
-
-	if (rcu_cpu_stall_suppress)
-		return;
-	rcp->ticks_this_gp++;
-	j = jiffies;
-	js = READ_ONCE(rcp->jiffies_stall);
-	if (rcp->rcucblist && ULONG_CMP_GE(j, js)) {
-		pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
-		       rcp->name, rcp->ticks_this_gp, DYNTICK_TASK_EXIT_IDLE,
-		       jiffies - rcp->gp_start, rcp->qlen);
-		dump_stack();
-		WRITE_ONCE(rcp->jiffies_stall,
-			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
-	} else if (ULONG_CMP_GE(j, js)) {
-		WRITE_ONCE(rcp->jiffies_stall,
-			   jiffies + rcu_jiffies_till_stall_check());
-	}
-}
-
-static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
-{
-	rcp->ticks_this_gp = 0;
-	rcp->gp_start = jiffies;
-	WRITE_ONCE(rcp->jiffies_stall,
-		   jiffies + rcu_jiffies_till_stall_check());
-}
-
-static void check_cpu_stalls(void)
-{
-	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk);)
-	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk);)
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */

tools/testing/selftests/rcutorture/configs/rcu/TINY02

@@ -6,7 +6,6 @@ CONFIG_PREEMPT=n
 CONFIG_HZ_PERIODIC=y
 CONFIG_NO_HZ_IDLE=n
 CONFIG_NO_HZ_FULL=n
-CONFIG_RCU_TRACE=y
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
 CONFIG_DEBUG_LOCK_ALLOC=y