srcu: Remove Classic SRCU

Classic SRCU was only ever intended to be a fallback in case of issues
with Tree/Tiny SRCU, and the latter two are doing quite well in testing.
This commit therefore removes Classic SRCU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

include/linux/srcu.h

@@ -60,8 +60,6 @@ int init_srcu_struct(struct srcu_struct *sp);
 #include <linux/srcutiny.h>
 #elif defined(CONFIG_TREE_SRCU)
 #include <linux/srcutree.h>
-#elif defined(CONFIG_CLASSIC_SRCU)
-#include <linux/srcuclassic.h>
 #elif defined(CONFIG_SRCU)
 #error "Unknown SRCU implementation specified to kernel configuration"
 #else

init/Kconfig

@@ -526,32 +526,15 @@ config SRCU
 	  permits arbitrary sleeping or blocking within RCU read-side critical
 	  sections.
 
-config CLASSIC_SRCU
-	bool "Use v4.11 classic SRCU implementation"
-	default n
-	depends on RCU_EXPERT && SRCU
-	help
-	  This option selects the traditional well-tested classic SRCU
-	  implementation from v4.11, as might be desired for enterprise
-	  Linux distributions.  Without this option, the shiny new
-	  Tiny SRCU and Tree SRCU implementations are used instead.
-	  At some point, it is hoped that Tiny SRCU and Tree SRCU
-	  will accumulate enough test time and confidence to allow
-	  Classic SRCU to be dropped entirely.
-
-	  Say Y if you need a rock-solid SRCU.
-
-	  Say N if you would like help test Tree SRCU.
-
 config TINY_SRCU
 	bool
-	default y if SRCU && TINY_RCU && !CLASSIC_SRCU
+	default y if SRCU && TINY_RCU
 	help
 	  This option selects the single-CPU non-preemptible version of SRCU.
 
 config TREE_SRCU
 	bool
-	default y if SRCU && !TINY_RCU && !CLASSIC_SRCU
+	default y if SRCU && !TINY_RCU
 	help
 	  This option selects the full-fledged version of SRCU.
 

kernel/rcu/Makefile

@@ -3,7 +3,6 @@
 KCOV_INSTRUMENT := n
 
 obj-y += update.o sync.o
-obj-$(CONFIG_CLASSIC_SRCU) += srcu.o
 obj-$(CONFIG_TREE_SRCU) += srcutree.o
 obj-$(CONFIG_TINY_SRCU) += srcutiny.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o

kernel/rcu/rcu.h

@@ -457,22 +457,6 @@ void srcutorture_get_gp_data(enum rcutorture_type test_type,
 			     struct srcu_struct *sp, int *flags,
 			     unsigned long *gpnum, unsigned long *completed);
 
-#elif defined(CONFIG_CLASSIC_SRCU)
-
-static inline void srcutorture_get_gp_data(enum rcutorture_type test_type,
-					   struct srcu_struct *sp, int *flags,
-					   unsigned long *gpnum,
-					   unsigned long *completed)
-{
-	if (test_type != SRCU_FLAVOR)
-		return;
-	*flags = 0;
-	*completed = sp->completed;
-	*gpnum = *completed;
-	if (sp->batch_queue.head || sp->batch_check0.head || sp->batch_check1.head)
-		(*gpnum)++;
-}
-
 #endif
 
 #ifdef CONFIG_TINY_RCU

kernel/rcu/rcutorture.c

@@ -564,45 +564,28 @@ static void srcu_torture_stats(void)
 	int __maybe_unused cpu;
 	int idx;
 
-#if defined(CONFIG_TREE_SRCU) || defined(CONFIG_CLASSIC_SRCU)
 #ifdef CONFIG_TREE_SRCU
 	idx = srcu_ctlp->srcu_idx & 0x1;
-#else /* #ifdef CONFIG_TREE_SRCU */
-	idx = srcu_ctlp->completed & 0x1;
-#endif /* #else #ifdef CONFIG_TREE_SRCU */
 	pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
 		 torture_type, TORTURE_FLAG, idx);
 	for_each_possible_cpu(cpu) {
 		unsigned long l0, l1;
 		unsigned long u0, u1;
 		long c0, c1;
-#ifdef CONFIG_TREE_SRCU
 		struct srcu_data *counts;
 
 		counts = per_cpu_ptr(srcu_ctlp->sda, cpu);
 		u0 = counts->srcu_unlock_count[!idx];
 		u1 = counts->srcu_unlock_count[idx];
-#else /* #ifdef CONFIG_TREE_SRCU */
-		struct srcu_array *counts;
-
-		counts = per_cpu_ptr(srcu_ctlp->per_cpu_ref, cpu);
-		u0 = counts->unlock_count[!idx];
-		u1 = counts->unlock_count[idx];
-#endif /* #else #ifdef CONFIG_TREE_SRCU */
 
 		/*
 		 * Make sure that a lock is always counted if the corresponding
 		 * unlock is counted.
 		 */
 		smp_rmb();
 
-#ifdef CONFIG_TREE_SRCU
 		l0 = counts->srcu_lock_count[!idx];
 		l1 = counts->srcu_lock_count[idx];
-#else /* #ifdef CONFIG_TREE_SRCU */
-		l0 = counts->lock_count[!idx];
-		l1 = counts->lock_count[idx];
-#endif /* #else #ifdef CONFIG_TREE_SRCU */
 
 		c0 = l0 - u0;
 		c1 = l1 - u1;