rcu: Make SRCU mandatory

Kernels configured with CONFIG_PRINTK=n and CONFIG_SRCU=n get build failures. This causes trouble for deep embedded systems. But given that there are more than 25 instances of "select SRCU" in the kernel, it is hard to believe that there are many kernels running in production without SRCU. This commit therefore makes SRCU mandatory. The SRCU Kconfig option remains for backwards compatibility, and will be removed when it is no longer used. Reported-by: John Ogness <john.ogness@linutronix.de> Reported-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: <linux-arch@vger.kernel.org> Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested Reviewed-by: John Ogness <john.ogness@linutronix.de>
ammarfaizi2 · Nov 23, 2022 · 4e3f7d2 · 4e3f7d2
1 parent 485cb93
commit 4e3f7d2
Show file tree

Hide file tree

Showing 6 changed files with 13 additions and 33 deletions.
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
@@ -152,11 +152,7 @@ static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 	return false;
 }
 static inline void rcu_preempt_deferred_qs(struct task_struct *t) { }
-#ifdef CONFIG_SRCU
 void rcu_scheduler_starting(void);
-#else /* #ifndef CONFIG_SRCU */
-static inline void rcu_scheduler_starting(void) { }
-#endif /* #else #ifndef CONFIG_SRCU */
 static inline void rcu_end_inkernel_boot(void) { }
 static inline bool rcu_inkernel_boot_has_ended(void) { return true; }
 static inline bool rcu_is_watching(void) { return true; }

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
@@ -78,11 +78,7 @@ static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 }
 #endif /* CONFIG_NEED_SRCU_NMI_SAFE */
 
-#ifdef CONFIG_SRCU
 void srcu_init(void);
-#else /* #ifdef CONFIG_SRCU */
-static inline void srcu_init(void) { }
-#endif /* #else #ifdef CONFIG_SRCU */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
@@ -54,21 +54,17 @@ config RCU_EXPERT
 	  Say N if you are unsure.
 
 config SRCU
-	bool
-	help
-	  This option selects the sleepable version of RCU. This version
-	  permits arbitrary sleeping or blocking within RCU read-side critical
-	  sections.
+	def_bool y
 
 config TINY_SRCU
 	bool
-	default y if SRCU && TINY_RCU
+	default y if TINY_RCU
 	help
 	  This option selects the single-CPU non-preemptible version of SRCU.
 
 config TREE_SRCU
 	bool
-	default y if SRCU && !TINY_RCU
+	default y if !TINY_RCU
 	help
 	  This option selects the full-fledged version of SRCU.
 
@@ -77,7 +73,6 @@ config NEED_SRCU_NMI_SAFE
 
 config TASKS_RCU_GENERIC
 	def_bool TASKS_RCU || TASKS_RUDE_RCU || TASKS_TRACE_RCU
-	select SRCU
 	help
 	  This option enables generic infrastructure code supporting
 	  task-based RCU implementations.  Not for manual selection.

diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
@@ -27,7 +27,6 @@ config RCU_SCALE_TEST
 	tristate "performance tests for RCU"
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
-	select SRCU
 	default n
 	help
 	  This option provides a kernel module that runs performance
@@ -43,7 +42,6 @@ config RCU_TORTURE_TEST
 	tristate "torture tests for RCU"
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
-	select SRCU
 	default n
 	help
 	  This option provides a kernel module that runs torture tests
@@ -59,7 +57,6 @@ config RCU_REF_SCALE_TEST
 	tristate "Scalability tests for read-side synchronization (RCU and others)"
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
-	select SRCU
 	default n
 	help
 	  This option provides a kernel module that runs performance tests

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
@@ -287,7 +287,7 @@ void rcu_test_sync_prims(void);
  */
 extern void resched_cpu(int cpu);
 
-#if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU)
+#if !defined(CONFIG_TINY_RCU)
 
 #include <linux/rcu_node_tree.h>
 
@@ -438,7 +438,7 @@ do {									\
 #define raw_lockdep_assert_held_rcu_node(p)				\
 	lockdep_assert_held(&ACCESS_PRIVATE(p, lock))
 
-#endif /* #if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU) */
+#endif /* !defined(CONFIG_TINY_RCU) */
 
 #ifdef CONFIG_TINY_RCU
 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
@@ -224,7 +224,7 @@ void rcu_test_sync_prims(void)
 	synchronize_rcu_expedited();
 }
 
-#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
+#if !defined(CONFIG_TINY_RCU)
 
 /*
  * Switch to run-time mode once RCU has fully initialized.
@@ -239,7 +239,7 @@ static int __init rcu_set_runtime_mode(void)
 }
 core_initcall(rcu_set_runtime_mode);
 
-#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
+#endif /* #if !defined(CONFIG_TINY_RCU) */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key rcu_lock_key;
@@ -561,10 +561,8 @@ static void early_boot_test_call_rcu(void)
 	struct early_boot_kfree_rcu *rhp;
 
 	call_rcu(&head, test_callback);
-	if (IS_ENABLED(CONFIG_SRCU)) {
-		early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
-		call_srcu(&early_srcu, &shead, test_callback);
-	}
+	early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
+	call_srcu(&early_srcu, &shead, test_callback);
 	rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
 	if (!WARN_ON_ONCE(!rhp))
 		kfree_rcu(rhp, rh);
@@ -587,12 +585,10 @@ static int rcu_verify_early_boot_tests(void)
 	if (rcu_self_test) {
 		early_boot_test_counter++;
 		rcu_barrier();
-		if (IS_ENABLED(CONFIG_SRCU)) {
-			early_boot_test_counter++;
-			srcu_barrier(&early_srcu);
-			WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
-			cleanup_srcu_struct(&early_srcu);
-		}
+		early_boot_test_counter++;
+		srcu_barrier(&early_srcu);
+		WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
+		cleanup_srcu_struct(&early_srcu);
 	}
 	if (rcu_self_test_counter != early_boot_test_counter) {
 		WARN_ON(1);