Subject: [PATCH] srcu: Isolate srcu sections using CONFIG_SRCU

From: Pranith Kumar <[email-masked]>
Date: Sat, 27 Dec 2014 12:17:43 -0500

Isolate the SRCU functions and data structures within CONFIG_SRCU so that there
is a compile time failure if srcu is used when not enabled. This was decided to
be better than waiting until link time for a failure to occur.

There are places which include kvm headers and utilize kvm data structures
without checking if KVM is enabled. In two such archs(s390, ppc64), the current
patch makes the uses of KVM conditional on KVM being enabled. The other option,
which is to enable KVM unconditionally seemed a bit too much as we could easily
figure out KVM only parts and enclose them in ifdefs.

Signed-off-by: Pranith Kumar <[email-masked]>
---
 arch/powerpc/kernel/setup_64.c |  7 ++++++-
 arch/s390/kernel/asm-offsets.c |  7 ++++++-
 include/linux/notifier.h       | 47 ++++++++++++++++++++++++------------------
 include/linux/srcu.h           |  6 +++++-
 4 files changed, 44 insertions(+), 23 deletions(-)

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 4f3cfe1..f55302f 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -65,10 +65,13 @@
 #include <asm/kexec.h>
 #include <asm/mmu_context.h>
 #include <asm/code-patching.h>
-#include <asm/kvm_ppc.h>
 #include <asm/hugetlb.h>
 #include <asm/epapr_hcalls.h>
 
+#if IS_ENABLED(CONFIG_KVM)
+#include <asm/kvm_ppc.h>
+#endif
+
 #ifdef DEBUG
 #define DBG(fmt...) udbg_printf(fmt)
 #else
@@ -286,8 +289,10 @@ void __init early_setup(unsigned long dt_ptr)
 	 */
 	cpu_ready_for_interrupts();
 
+#if IS_ENABLED(CONFIG_KVM)
 	/* Reserve large chunks of memory for use by CMA for KVM */
 	kvm_cma_reserve();
+#endif
 
 	/*
 	 * Reserve any gigantic pages requested on the command line.
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index ef279a1..2813a3c 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -7,12 +7,15 @@
 #define ASM_OFFSETS_C
 
 #include <linux/kbuild.h>
-#include <linux/kvm_host.h>
 #include <linux/sched.h>
 #include <asm/idle.h>
 #include <asm/vdso.h>
 #include <asm/pgtable.h>
 
+#if IS_ENABLED(CONFIG_KVM)
+#include <linux/kvm_host.h>
+#endif
+
 /*
  * Make sure that the compiler is new enough. We want a compiler that
  * is known to work with the "Q" assembler constraint.
@@ -182,8 +185,10 @@ int main(void)
 	DEFINE(__LC_PGM_TDB, offsetof(struct _lowcore, pgm_tdb));
 	DEFINE(__THREAD_trap_tdb, offsetof(struct task_struct, thread.trap_tdb));
 	DEFINE(__GMAP_ASCE, offsetof(struct gmap, asce));
+#if IS_ENABLED(CONFIG_KVM)
 	DEFINE(__SIE_PROG0C, offsetof(struct kvm_s390_sie_block, prog0c));
 	DEFINE(__SIE_PROG20, offsetof(struct kvm_s390_sie_block, prog20));
+#endif /* CONFIG_KVM */
 #endif /* CONFIG_32BIT */
 	return 0;
 }
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index d14a4c3..fe4f02a 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -47,6 +47,8 @@
  * runtime initialization.
  */
 
+struct notifier_block;
+
 typedef	int (*notifier_fn_t)(struct notifier_block *nb,
 			unsigned long action, void *data);
 
@@ -70,12 +72,6 @@ struct raw_notifier_head {
 	struct notifier_block __rcu *head;
 };
 
-struct srcu_notifier_head {
-	struct mutex mutex;
-	struct srcu_struct srcu;
-	struct notifier_block __rcu *head;
-};
-
 #define ATOMIC_INIT_NOTIFIER_HEAD(name) do {	\
 		spin_lock_init(&(name)->lock);	\
 		(name)->head = NULL;		\
@@ -88,11 +84,6 @@ struct srcu_notifier_head {
 		(name)->head = NULL;		\
 	} while (0)
 
-/* srcu_notifier_heads must be initialized and cleaned up dynamically */
-extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
-#define srcu_cleanup_notifier_head(name)	\
-		cleanup_srcu_struct(&(name)->srcu);
-
 #define ATOMIC_NOTIFIER_INIT(name) {				\
 		.lock = __SPIN_LOCK_UNLOCKED(name.lock),	\
 		.head = NULL }
@@ -101,7 +92,6 @@ extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
 		.head = NULL }
 #define RAW_NOTIFIER_INIT(name)	{				\
 		.head = NULL }
-/* srcu_notifier_heads cannot be initialized statically */
 
 #define ATOMIC_NOTIFIER_HEAD(name)				\
 	struct atomic_notifier_head name =			\
@@ -121,8 +111,6 @@ extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 		struct notifier_block *nb);
 extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 		struct notifier_block *nb);
-extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
-		struct notifier_block *nb);
 
 extern int blocking_notifier_chain_cond_register(
 		struct blocking_notifier_head *nh,
@@ -134,8 +122,6 @@ extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
 		struct notifier_block *nb);
 extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
 		struct notifier_block *nb);
-extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
-		struct notifier_block *nb);
 
 extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 		unsigned long val, void *v);
@@ -149,10 +135,6 @@ extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
 		unsigned long val, void *v);
 extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
 	unsigned long val, void *v, int nr_to_call, int *nr_calls);
-extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
-		unsigned long val, void *v);
-extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
-	unsigned long val, void *v, int nr_to_call, int *nr_calls);
 
 #define NOTIFY_DONE		0x0000		/* Don't care */
 #define NOTIFY_OK		0x0001		/* Suits me */
@@ -211,5 +193,30 @@ static inline int notifier_to_errno(int ret)
 
 extern struct blocking_notifier_head reboot_notifier_list;
 
+#ifdef CONFIG_SRCU
+
+struct srcu_notifier_head {
+	struct mutex mutex;
+	struct srcu_struct srcu;
+	struct notifier_block __rcu *head;
+};
+
+/* srcu_notifier_heads must be initialized and cleaned up dynamically
+ * srcu_notifier_heads cannot be initialized statically
+ */
+extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
+#define srcu_cleanup_notifier_head(name) cleanup_srcu_struct(&(name)->srcu)
+
+extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
+		struct notifier_block *nb);
+extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
+		struct notifier_block *nb);
+extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
+		unsigned long val, void *v);
+extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
+	unsigned long val, void *v, int nr_to_call, int *nr_calls);
+
+#endif /* CONFIG_SRCU */
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 9cfd962..ed9c389 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -26,6 +26,8 @@
  *
  */
 
+#ifdef CONFIG_SRCU
+
 #ifndef _LINUX_SRCU_H
 #define _LINUX_SRCU_H
 
@@ -249,4 +251,6 @@ static inline void smp_mb__after_srcu_read_unlock(void)
 	/* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
 }
 
-#endif
+#endif /* _LINUX_SRCU_H */
+
+#endif /* CONFIG_SRCU */
-- 
1.9.1