rcu: Remove debugfs tracing

RCU's debugfs tracing used to be the only reasonable low-level debug
information available, but ftrace and event tracing has since surpassed
the RCU debugfs level of usefulness.  This commit therefore removes
RCU's debugfs tracing.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Documentation/RCU/00-INDEX

@@ -28,8 +28,6 @@ stallwarn.txt
 	- RCU CPU stall warnings (module parameter rcu_cpu_stall_suppress)
 torture.txt
 	- RCU Torture Test Operation (CONFIG_RCU_TORTURE_TEST)
-trace.txt
-	- CONFIG_RCU_TRACE debugfs files and formats
 UP.txt
 	- RCU on Uniprocessor Systems
 whatisRCU.txt

Documentation/RCU/Design/Requirements/Requirements.html

@@ -2034,7 +2034,7 @@ guard against mishaps and misuse:
 	some other synchronization mechanism, for example, reference
 	counting.
 <li>	In kernels built with <tt>CONFIG_RCU_TRACE=y</tt>, RCU-related
-	information is provided via both debugfs and event tracing.
+	information is provided via event tracing.
 <li>	Open-coded use of <tt>rcu_assign_pointer()</tt> and
 	<tt>rcu_dereference()</tt> to create typical linked
 	data structures can be surprisingly error-prone.

init/Kconfig

@@ -659,14 +659,6 @@ config RCU_FAST_NO_HZ
 
 	  Say N if you are unsure.
 
-config TREE_RCU_TRACE
-	def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
-	select DEBUG_FS
-	help
-	  This option provides tracing for the TREE_RCU and
-	  PREEMPT_RCU implementations, permitting Makefile to
-	  trivially select kernel/rcutree_trace.c.
-
 config RCU_BOOST
 	bool "Enable RCU priority boosting"
 	depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT

kernel/rcu/Makefile

@@ -9,6 +9,5 @@ obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
 obj-$(CONFIG_TREE_RCU) += tree.o
 obj-$(CONFIG_PREEMPT_RCU) += tree.o
-obj-$(CONFIG_TREE_RCU_TRACE) += tree_trace.o
 obj-$(CONFIG_TINY_RCU) += tiny.o
 obj-$(CONFIG_RCU_NEED_SEGCBLIST) += rcu_segcblist.o

kernel/rcu/tiny_plugin.h

@@ -24,8 +24,6 @@
 
 #include <linux/kthread.h>
 #include <linux/init.h>
-#include <linux/debugfs.h>
-#include <linux/seq_file.h>
 
 /* Global control variables for rcupdate callback mechanism. */
 struct rcu_ctrlblk {
@@ -87,49 +85,6 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
 	local_irq_restore(flags);
 }
 
-/*
- * Dump statistics for TINY_RCU, such as they are.
- */
-static int show_tiny_stats(struct seq_file *m, void *unused)
-{
-	seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
-	seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
-	return 0;
-}
-
-static int show_tiny_stats_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, show_tiny_stats, NULL);
-}
-
-static const struct file_operations show_tiny_stats_fops = {
-	.owner = THIS_MODULE,
-	.open = show_tiny_stats_open,
-	.read = seq_read,
-	.llseek = seq_lseek,
-	.release = single_release,
-};
-
-static struct dentry *rcudir;
-
-static int __init rcutiny_trace_init(void)
-{
-	struct dentry *retval;
-
-	rcudir = debugfs_create_dir("rcu", NULL);
-	if (!rcudir)
-		goto free_out;
-	retval = debugfs_create_file("rcudata", 0444, rcudir,
-				     NULL, &show_tiny_stats_fops);
-	if (!retval)
-		goto free_out;
-	return 0;
-free_out:
-	debugfs_remove_recursive(rcudir);
-	return 1;
-}
-device_initcall(rcutiny_trace_init);
-
 static void check_cpu_stall(struct rcu_ctrlblk *rcp)
 {
 	unsigned long j;

kernel/rcu/tree.h

@@ -152,19 +152,6 @@ struct rcu_node {
 				/* Number of tasks boosted for expedited GP. */
 	unsigned long n_normal_boosts;
 				/* Number of tasks boosted for normal GP. */
-	unsigned long n_balk_blkd_tasks;
-				/* Refused to boost: no blocked tasks. */
-	unsigned long n_balk_exp_gp_tasks;
-				/* Refused to boost: nothing blocking GP. */
-	unsigned long n_balk_boost_tasks;
-				/* Refused to boost: already boosting. */
-	unsigned long n_balk_notblocked;
-				/* Refused to boost: RCU RS CS still running. */
-	unsigned long n_balk_notyet;
-				/* Refused to boost: not yet time. */
-	unsigned long n_balk_nos;
-				/* Refused to boost: not sure why, though. */
-				/*  This can happen due to race conditions. */
 #ifdef CONFIG_RCU_NOCB_CPU
 	struct swait_queue_head nocb_gp_wq[2];
 				/* Place for rcu_nocb_kthread() to wait GP. */
@@ -535,17 +522,3 @@ void srcu_offline_cpu(unsigned int cpu) { }
 #endif /* #else #ifdef CONFIG_SRCU */
 
 #endif /* #ifndef RCU_TREE_NONCORE */
-
-#ifdef CONFIG_RCU_TRACE
-/* Read out queue lengths for tracing. */
-static inline void rcu_nocb_q_lengths(struct rcu_data *rdp, long *ql, long *qll)
-{
-#ifdef CONFIG_RCU_NOCB_CPU
-	*ql = atomic_long_read(&rdp->nocb_q_count);
-	*qll = atomic_long_read(&rdp->nocb_q_count_lazy);
-#else /* #ifdef CONFIG_RCU_NOCB_CPU */
-	*ql = 0;
-	*qll = 0;
-#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
-}
-#endif /* #ifdef CONFIG_RCU_TRACE */

kernel/rcu/tree_plugin.h

@@ -70,7 +70,7 @@ static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */
 static void __init rcu_bootup_announce_oddness(void)
 {
 	if (IS_ENABLED(CONFIG_RCU_TRACE))
-		pr_info("\tRCU debugfs-based tracing is enabled.\n");
+		pr_info("\tRCU event tracing is enabled.\n");
 	if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
 	    (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
 		pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
@@ -899,33 +899,6 @@ void exit_rcu(void)
 
 #include "../locking/rtmutex_common.h"
 
-#ifdef CONFIG_RCU_TRACE
-
-static void rcu_initiate_boost_trace(struct rcu_node *rnp)
-{
-	if (!rcu_preempt_has_tasks(rnp))
-		rnp->n_balk_blkd_tasks++;
-	else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
-		rnp->n_balk_exp_gp_tasks++;
-	else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
-		rnp->n_balk_boost_tasks++;
-	else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
-		rnp->n_balk_notblocked++;
-	else if (rnp->gp_tasks != NULL &&
-		 ULONG_CMP_LT(jiffies, rnp->boost_time))
-		rnp->n_balk_notyet++;
-	else
-		rnp->n_balk_nos++;
-}
-
-#else /* #ifdef CONFIG_RCU_TRACE */
-
-static void rcu_initiate_boost_trace(struct rcu_node *rnp)
-{
-}
-
-#endif /* #else #ifdef CONFIG_RCU_TRACE */
-
 static void rcu_wake_cond(struct task_struct *t, int status)
 {
 	/*
@@ -1058,7 +1031,6 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 
 	lockdep_assert_held(&rnp->lock);
 	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
-		rnp->n_balk_exp_gp_tasks++;
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		return;
 	}
@@ -1074,7 +1046,6 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 		if (t)
 			rcu_wake_cond(t, rnp->boost_kthread_status);
 	} else {
-		rcu_initiate_boost_trace(rnp);
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	}
 }

lib/Kconfig.debug

@@ -1361,9 +1361,8 @@ config RCU_TRACE
 	default y if TREE_RCU
 	select TRACE_CLOCK
 	help
-	  This option provides tracing in RCU which presents stats
-	  in debugfs for debugging RCU implementation.  It also enables
-	  additional tracepoints for ftrace-style event tracing.
+	  This option enables additional tracepoints for ftrace-style
+	  event tracing.
 
 	  Say Y here if you want to enable RCU tracing
 	  Say N if you are unsure.

tools/testing/selftests/rcutorture/configs/rcu/TREE02-T

-CONFIG_SMP=y
-CONFIG_NR_CPUS=8
-CONFIG_PREEMPT_NONE=n
-CONFIG_PREEMPT_VOLUNTARY=n
-CONFIG_PREEMPT=y
-#CHECK#CONFIG_PREEMPT_RCU=y
-CONFIG_HZ_PERIODIC=n
-CONFIG_NO_HZ_IDLE=y
-CONFIG_NO_HZ_FULL=n
-CONFIG_RCU_FAST_NO_HZ=n
-CONFIG_RCU_TRACE=y
-CONFIG_HOTPLUG_CPU=n
-CONFIG_SUSPEND=n
-CONFIG_HIBERNATION=n
-CONFIG_RCU_FANOUT=3
-CONFIG_RCU_FANOUT_LEAF=3
-CONFIG_RCU_NOCB_CPU=n
-CONFIG_DEBUG_LOCK_ALLOC=y
-CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
-CONFIG_DEBUG_OBJECTS_RCU_HEAD=n

tools/testing/selftests/rcutorture/configs/rcu/TREE08-T

-CONFIG_SMP=y
-CONFIG_NR_CPUS=16
-CONFIG_PREEMPT_NONE=n
-CONFIG_PREEMPT_VOLUNTARY=n
-CONFIG_PREEMPT=y
-#CHECK#CONFIG_PREEMPT_RCU=y
-CONFIG_HZ_PERIODIC=n
-CONFIG_NO_HZ_IDLE=y
-CONFIG_NO_HZ_FULL=n
-CONFIG_RCU_FAST_NO_HZ=n
-CONFIG_RCU_TRACE=y
-CONFIG_HOTPLUG_CPU=n
-CONFIG_SUSPEND=n
-CONFIG_HIBERNATION=n
-CONFIG_RCU_FANOUT=3
-CONFIG_RCU_FANOUT_LEAF=2
-CONFIG_RCU_NOCB_CPU=y
-CONFIG_RCU_NOCB_CPU_ALL=y
-CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_BOOST=n
-CONFIG_DEBUG_OBJECTS_RCU_HEAD=n

tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt

@@ -79,9 +79,5 @@ CONFIG_TASKS_RCU
 
 	Selected by CONFIG_RCU_TORTURE_TEST, so cannot disable.
 
-CONFIG_RCU_TRACE
-
-	Implied by CONFIG_RCU_TRACE for Tree RCU.
-
 
 boot parameters ignored: TBD