Merge tag 'locking-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar:
 "Core locking primitives updates:
    - Remove mutex_trylock_recursive() from the API - no users left
    - Simplify + constify the futex code a bit

  Lockdep updates:
    - Teach lockdep about local_lock_t
    - Add CONFIG_DEBUG_IRQFLAGS=y debug config option to check for
      potentially unsafe IRQ mask restoration patterns. (I.e.
      calling raw_local_irq_restore() with IRQs enabled.)
    - Add wait context self-tests
    - Fix graph lock corner case corrupting internal data structures
    - Fix noinstr annotations

  LKMM updates:
    - Simplify the litmus tests
    - Documentation fixes

  KCSAN updates:
    - Re-enable KCSAN instrumentation in lib/random32.c

  Misc fixes:
    - Don't branch-trace static label APIs
    - DocBook fix
    - Remove stale leftover empty file"

* tag 'locking-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
  checkpatch: Don't check for mutex_trylock_recursive()
  locking/mutex: Kill mutex_trylock_recursive()
  s390: Use arch_local_irq_{save,restore}() in early boot code
  lockdep: Noinstr annotate warn_bogus_irq_restore()
  locking/lockdep: Avoid unmatched unlock
  locking/rwsem: Remove empty rwsem.h
  locking/rtmutex: Add missing kernel-doc markup
  futex: Remove unneeded gotos
  futex: Change utime parameter to be 'const ... *'
  lockdep: report broken irq restoration
  jump_label: Do not profile branch annotations
  locking: Add Reviewers
  locking/selftests: Add local_lock inversion tests
  locking/lockdep: Exclude local_lock_t from IRQ inversions
  locking/lockdep: Clean up check_redundant() a bit
  locking/lockdep: Add a skip() function to __bfs()
  locking/lockdep: Mark local_lock_t
  locking/selftests: More granular debug_locks_verbose
  lockdep/selftest: Add wait context selftests
  tools/memory-model: Fix typo in klitmus7 compatibility table
  ...

Documentation/admin-guide/kernel-parameters.txt

@@ -802,13 +802,14 @@
 			insecure, please do not use on production kernels.
 
 	debug_locks_verbose=
-			[KNL] verbose self-tests
-			Format=<0|1>
+			[KNL] verbose locking self-tests
+			Format: <int>
 			Print debugging info while doing the locking API
 			self-tests.
-			We default to 0 (no extra messages), setting it to
-			1 will print _a lot_ more information - normally
-			only useful to kernel developers.
+			Bitmask for the various LOCKTYPE_ tests. Defaults to 0
+			(no extra messages), setting it to -1 (all bits set)
+			will print _a_lot_ more information - normally only
+			useful to lockdep developers.
 
 	debug_objects	[KNL] Enable object debugging
 

MAINTAINERS

@@ -10342,6 +10342,8 @@ LOCKING PRIMITIVES
 M:	Peter Zijlstra <peterz@infradead.org>
 M:	Ingo Molnar <mingo@redhat.com>
 M:	Will Deacon <will@kernel.org>
+R:	Waiman Long <longman@redhat.com>
+R:	Boqun Feng <boqun.feng@gmail.com> (LOCKDEP)
 L:	linux-kernel@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking/core

drivers/s390/char/sclp_early_core.c

@@ -66,13 +66,13 @@ int sclp_early_cmd(sclp_cmdw_t cmd, void *sccb)
 	unsigned long flags;
 	int rc;
 
-	raw_local_irq_save(flags);
+	flags = arch_local_irq_save();
 	rc = sclp_service_call(cmd, sccb);
 	if (rc)
 		goto out;
 	sclp_early_wait_irq();
 out:
-	raw_local_irq_restore(flags);
+	arch_local_irq_restore(flags);
 	return rc;
 }
 

include/linux/compiler.h

@@ -76,6 +76,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #else
 # define likely(x)	__builtin_expect(!!(x), 1)
 # define unlikely(x)	__builtin_expect(!!(x), 0)
+# define likely_notrace(x)	likely(x)
+# define unlikely_notrace(x)	unlikely(x)
 #endif
 
 /* Optimization barrier */

include/linux/irqflags.h

@@ -149,6 +149,17 @@ do {						\
 # define start_critical_timings() do { } while (0)
 #endif
 
+#ifdef CONFIG_DEBUG_IRQFLAGS
+extern void warn_bogus_irq_restore(void);
+#define raw_check_bogus_irq_restore()			\
+	do {						\
+		if (unlikely(!arch_irqs_disabled()))	\
+			warn_bogus_irq_restore();	\
+	} while (0)
+#else
+#define raw_check_bogus_irq_restore() do { } while (0)
+#endif
+
 /*
  * Wrap the arch provided IRQ routines to provide appropriate checks.
  */
@@ -162,6 +173,7 @@ do {						\
 #define raw_local_irq_restore(flags)			\
 	do {						\
 		typecheck(unsigned long, flags);	\
+		raw_check_bogus_irq_restore();		\
 		arch_local_irq_restore(flags);		\
 	} while (0)
 #define raw_local_save_flags(flags)			\

include/linux/jump_label.h

@@ -261,14 +261,14 @@ static __always_inline void jump_label_init(void)
 
 static __always_inline bool static_key_false(struct static_key *key)
 {
-	if (unlikely(static_key_count(key) > 0))
+	if (unlikely_notrace(static_key_count(key) > 0))
 		return true;
 	return false;
 }
 
 static __always_inline bool static_key_true(struct static_key *key)
 {
-	if (likely(static_key_count(key) > 0))
+	if (likely_notrace(static_key_count(key) > 0))
 		return true;
 	return false;
 }
@@ -460,7 +460,7 @@ extern bool ____wrong_branch_error(void);
 		branch = !arch_static_branch_jump(&(x)->key, true);		\
 	else									\
 		branch = ____wrong_branch_error();				\
-	likely(branch);								\
+	likely_notrace(branch);								\
 })
 
 #define static_branch_unlikely(x)						\
@@ -472,13 +472,13 @@ extern bool ____wrong_branch_error(void);
 		branch = arch_static_branch(&(x)->key, false);			\
 	else									\
 		branch = ____wrong_branch_error();				\
-	unlikely(branch);							\
+	unlikely_notrace(branch);							\
 })
 
 #else /* !CONFIG_JUMP_LABEL */
 
-#define static_branch_likely(x)		likely(static_key_enabled(&(x)->key))
-#define static_branch_unlikely(x)	unlikely(static_key_enabled(&(x)->key))
+#define static_branch_likely(x)		likely_notrace(static_key_enabled(&(x)->key))
+#define static_branch_unlikely(x)	unlikely_notrace(static_key_enabled(&(x)->key))
 
 #endif /* CONFIG_JUMP_LABEL */
 

include/linux/local_lock_internal.h

@@ -18,6 +18,7 @@ typedef struct {
 	.dep_map = {					\
 		.name = #lockname,			\
 		.wait_type_inner = LD_WAIT_CONFIG,	\
+		.lock_type = LD_LOCK_PERCPU,			\
 	}
 #else
 # define LL_DEP_MAP_INIT(lockname)
@@ -30,7 +31,9 @@ do {								\
 	static struct lock_class_key __key;			\
 								\
 	debug_check_no_locks_freed((void *)lock, sizeof(*lock));\
-	lockdep_init_map_wait(&(lock)->dep_map, #lock, &__key, 0, LD_WAIT_CONFIG);\
+	lockdep_init_map_type(&(lock)->dep_map, #lock, &__key, 0, \
+			      LD_WAIT_CONFIG, LD_WAIT_INV,	\
+			      LD_LOCK_PERCPU);			\
 } while (0)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC

include/linux/lockdep.h

@@ -185,12 +185,19 @@ extern void lockdep_unregister_key(struct lock_class_key *key);
  * to lockdep:
  */
 
-extern void lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
-	struct lock_class_key *key, int subclass, short inner, short outer);
+extern void lockdep_init_map_type(struct lockdep_map *lock, const char *name,
+	struct lock_class_key *key, int subclass, u8 inner, u8 outer, u8 lock_type);
+
+static inline void
+lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
+		       struct lock_class_key *key, int subclass, u8 inner, u8 outer)
+{
+	lockdep_init_map_type(lock, name, key, subclass, inner, LD_WAIT_INV, LD_LOCK_NORMAL);
+}
 
 static inline void
 lockdep_init_map_wait(struct lockdep_map *lock, const char *name,
-		      struct lock_class_key *key, int subclass, short inner)
+		      struct lock_class_key *key, int subclass, u8 inner)
 {
 	lockdep_init_map_waits(lock, name, key, subclass, inner, LD_WAIT_INV);
 }
@@ -340,6 +347,8 @@ static inline void lockdep_set_selftest_task(struct task_struct *task)
 # define lock_set_class(l, n, k, s, i)		do { } while (0)
 # define lock_set_subclass(l, s, i)		do { } while (0)
 # define lockdep_init()				do { } while (0)
+# define lockdep_init_map_type(lock, name, key, sub, inner, outer, type) \
+		do { (void)(name); (void)(key); } while (0)
 # define lockdep_init_map_waits(lock, name, key, sub, inner, outer) \
 		do { (void)(name); (void)(key); } while (0)
 # define lockdep_init_map_wait(lock, name, key, sub, inner) \

include/linux/lockdep_types.h

@@ -30,6 +30,12 @@ enum lockdep_wait_type {
 	LD_WAIT_MAX,		/* must be last */
 };
 
+enum lockdep_lock_type {
+	LD_LOCK_NORMAL = 0,	/* normal, catch all */
+	LD_LOCK_PERCPU,		/* percpu */
+	LD_LOCK_MAX,
+};
+
 #ifdef CONFIG_LOCKDEP
 
 /*
@@ -119,8 +125,10 @@ struct lock_class {
 	int				name_version;
 	const char			*name;
 
-	short				wait_type_inner;
-	short				wait_type_outer;
+	u8				wait_type_inner;
+	u8				wait_type_outer;
+	u8				lock_type;
+	/* u8				hole; */
 
 #ifdef CONFIG_LOCK_STAT
 	unsigned long			contention_point[LOCKSTAT_POINTS];
@@ -169,8 +177,10 @@ struct lockdep_map {
 	struct lock_class_key		*key;
 	struct lock_class		*class_cache[NR_LOCKDEP_CACHING_CLASSES];
 	const char			*name;
-	short				wait_type_outer; /* can be taken in this context */
-	short				wait_type_inner; /* presents this context */
+	u8				wait_type_outer; /* can be taken in this context */
+	u8				wait_type_inner; /* presents this context */
+	u8				lock_type;
+	/* u8				hole; */
 #ifdef CONFIG_LOCK_STAT
 	int				cpu;
 	unsigned long			ip;

include/linux/mutex.h

@@ -199,29 +199,4 @@ extern void mutex_unlock(struct mutex *lock);
 
 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 
-/*
- * These values are chosen such that FAIL and SUCCESS match the
- * values of the regular mutex_trylock().
- */
-enum mutex_trylock_recursive_enum {
-	MUTEX_TRYLOCK_FAILED    = 0,
-	MUTEX_TRYLOCK_SUCCESS   = 1,
-	MUTEX_TRYLOCK_RECURSIVE,
-};
-
-/**
- * mutex_trylock_recursive - trylock variant that allows recursive locking
- * @lock: mutex to be locked
- *
- * This function should not be used, _ever_. It is purely for hysterical GEM
- * raisins, and once those are gone this will be removed.
- *
- * Returns:
- *  - MUTEX_TRYLOCK_FAILED    - trylock failed,
- *  - MUTEX_TRYLOCK_SUCCESS   - lock acquired,
- *  - MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
- */
-extern /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
-mutex_trylock_recursive(struct mutex *lock);
-
 #endif /* __LINUX_MUTEX_H */

include/linux/syscalls.h

@@ -607,11 +607,11 @@ asmlinkage long sys_unshare(unsigned long unshare_flags);
 
 /* kernel/futex.c */
 asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
-			struct __kernel_timespec __user *utime, u32 __user *uaddr2,
-			u32 val3);
+			  const struct __kernel_timespec __user *utime,
+			  u32 __user *uaddr2, u32 val3);
 asmlinkage long sys_futex_time32(u32 __user *uaddr, int op, u32 val,
-			struct old_timespec32 __user *utime, u32 __user *uaddr2,
-			u32 val3);
+				 const struct old_timespec32 __user *utime,
+				 u32 __user *uaddr2, u32 val3);
 asmlinkage long sys_get_robust_list(int pid,
 				    struct robust_list_head __user * __user *head_ptr,
 				    size_t __user *len_ptr);

kernel/futex.c

@@ -3012,7 +3012,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
 		 * Success, we're done! No tricky corner cases.
 		 */
 		if (!ret)
-			goto out_putkey;
+			return ret;
 		/*
 		 * The atomic access to the futex value generated a
 		 * pagefault, so retry the user-access and the wakeup:
@@ -3029,7 +3029,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
 		 * wake_futex_pi has detected invalid state. Tell user
 		 * space.
 		 */
-		goto out_putkey;
+		return ret;
 	}
 
 	/*
@@ -3050,7 +3050,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
 
 		default:
 			WARN_ON_ONCE(1);
-			goto out_putkey;
+			return ret;
 		}
 	}
 
@@ -3061,7 +3061,6 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
 
 out_unlock:
 	spin_unlock(&hb->lock);
-out_putkey:
 	return ret;
 
 pi_retry:
@@ -3763,8 +3762,8 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 
 
 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
-		struct __kernel_timespec __user *, utime, u32 __user *, uaddr2,
-		u32, val3)
+		const struct __kernel_timespec __user *, utime,
+		u32 __user *, uaddr2, u32, val3)
 {
 	struct timespec64 ts;
 	ktime_t t, *tp = NULL;
@@ -3959,7 +3958,7 @@ COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
 
 #ifdef CONFIG_COMPAT_32BIT_TIME
 SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
-		struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
+		const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
 		u32, val3)
 {
 	struct timespec64 ts;

kernel/kcsan/core.c

@@ -12,7 +12,6 @@
 #include <linux/moduleparam.h>
 #include <linux/percpu.h>
 #include <linux/preempt.h>
-#include <linux/random.h>
 #include <linux/sched.h>
 #include <linux/uaccess.h>
 
@@ -101,7 +100,7 @@ static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];
 static DEFINE_PER_CPU(long, kcsan_skip);
 
 /* For kcsan_prandom_u32_max(). */
-static DEFINE_PER_CPU(struct rnd_state, kcsan_rand_state);
+static DEFINE_PER_CPU(u32, kcsan_rand_state);
 
 static __always_inline atomic_long_t *find_watchpoint(unsigned long addr,
 						      size_t size,
@@ -275,20 +274,17 @@ should_watch(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *
 }
 
 /*
- * Returns a pseudo-random number in interval [0, ep_ro). See prandom_u32_max()
- * for more details.
- *
- * The open-coded version here is using only safe primitives for all contexts
- * where we can have KCSAN instrumentation. In particular, we cannot use
- * prandom_u32() directly, as its tracepoint could cause recursion.
+ * Returns a pseudo-random number in interval [0, ep_ro). Simple linear
+ * congruential generator, using constants from "Numerical Recipes".
  */
 static u32 kcsan_prandom_u32_max(u32 ep_ro)
 {
-	struct rnd_state *state = &get_cpu_var(kcsan_rand_state);
-	const u32 res = prandom_u32_state(state);
+	u32 state = this_cpu_read(kcsan_rand_state);
+
+	state = 1664525 * state + 1013904223;
+	this_cpu_write(kcsan_rand_state, state);
 
-	put_cpu_var(kcsan_rand_state);
-	return (u32)(((u64) res * ep_ro) >> 32);
+	return state % ep_ro;
 }
 
 static inline void reset_kcsan_skip(void)
@@ -639,10 +635,14 @@ static __always_inline void check_access(const volatile void *ptr, size_t size,
 
 void __init kcsan_init(void)
 {
+	int cpu;
+
 	BUG_ON(!in_task());
 
 	kcsan_debugfs_init();
-	prandom_seed_full_state(&kcsan_rand_state);
+
+	for_each_possible_cpu(cpu)
+		per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles();
 
 	/*
 	 * We are in the init task, and no other tasks should be running;

kernel/locking/Makefile

@@ -15,6 +15,7 @@ CFLAGS_REMOVE_mutex-debug.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_rtmutex-debug.o = $(CC_FLAGS_FTRACE)
 endif
 
+obj-$(CONFIG_DEBUG_IRQFLAGS) += irqflag-debug.o
 obj-$(CONFIG_DEBUG_MUTEXES) += mutex-debug.o
 obj-$(CONFIG_LOCKDEP) += lockdep.o
 ifeq ($(CONFIG_PROC_FS),y)

kernel/locking/irqflag-debug.c

+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/bug.h>
+#include <linux/export.h>
+#include <linux/irqflags.h>
+
+noinstr void warn_bogus_irq_restore(void)
+{
+	instrumentation_begin();
+	WARN_ONCE(1, "raw_local_irq_restore() called with IRQs enabled\n");
+	instrumentation_end();
+}
+EXPORT_SYMBOL(warn_bogus_irq_restore);

kernel/locking/mutex.c

@@ -86,16 +86,6 @@ bool mutex_is_locked(struct mutex *lock)
 }
 EXPORT_SYMBOL(mutex_is_locked);
 
-__must_check enum mutex_trylock_recursive_enum
-mutex_trylock_recursive(struct mutex *lock)
-{
-	if (unlikely(__mutex_owner(lock) == current))
-		return MUTEX_TRYLOCK_RECURSIVE;
-
-	return mutex_trylock(lock);
-}
-EXPORT_SYMBOL(mutex_trylock_recursive);
-
 static inline unsigned long __owner_flags(unsigned long owner)
 {
 	return owner & MUTEX_FLAGS;

kernel/locking/rtmutex.c

@@ -1604,8 +1604,11 @@ void __sched rt_mutex_unlock(struct rt_mutex *lock)
 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 
 /**
- * Futex variant, that since futex variants do not use the fast-path, can be
- * simple and will not need to retry.
+ * __rt_mutex_futex_unlock - Futex variant, that since futex variants
+ * do not use the fast-path, can be simple and will not need to retry.
+ *
+ * @lock:	The rt_mutex to be unlocked
+ * @wake_q:	The wake queue head from which to get the next lock waiter
  */
 bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
 				    struct wake_q_head *wake_q)
@@ -1662,13 +1665,15 @@ void rt_mutex_destroy(struct rt_mutex *lock)
 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
 
 /**
- * __rt_mutex_init - initialize the rt lock
+ * __rt_mutex_init - initialize the rt_mutex
  *
- * @lock: the rt lock to be initialized
+ * @lock:	The rt_mutex to be initialized
+ * @name:	The lock name used for debugging
+ * @key:	The lock class key used for debugging
  *
- * Initialize the rt lock to unlocked state.
+ * Initialize the rt_mutex to unlocked state.
  *
- * Initializing of a locked rt lock is not allowed
+ * Initializing of a locked rt_mutex is not allowed
  */
 void __rt_mutex_init(struct rt_mutex *lock, const char *name,
 		     struct lock_class_key *key)

lib/Kconfig.debug

@@ -1335,6 +1335,7 @@ config LOCKDEP_SMALL
 config DEBUG_LOCKDEP
 	bool "Lock dependency engine debugging"
 	depends on DEBUG_KERNEL && LOCKDEP
+	select DEBUG_IRQFLAGS
 	help
 	  If you say Y here, the lock dependency engine will do
 	  additional runtime checks to debug itself, at the price
@@ -1423,6 +1424,13 @@ config TRACE_IRQFLAGS_NMI
 	depends on TRACE_IRQFLAGS
 	depends on TRACE_IRQFLAGS_NMI_SUPPORT
 
+config DEBUG_IRQFLAGS
+	bool "Debug IRQ flag manipulation"
+	help
+	  Enables checks for potentially unsafe enabling or disabling of
+	  interrupts, such as calling raw_local_irq_restore() when interrupts
+	  are enabled.
+
 config STACKTRACE
 	bool "Stack backtrace support"
 	depends on STACKTRACE_SUPPORT

lib/Makefile

@@ -27,9 +27,6 @@ KASAN_SANITIZE_string.o := n
 CFLAGS_string.o += -fno-stack-protector
 endif
 
-# Used by KCSAN while enabled, avoid recursion.
-KCSAN_SANITIZE_random32.o := n
-
 lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 rbtree.o radix-tree.o timerqueue.o xarray.o \
 	 idr.o extable.o sha1.o irq_regs.o argv_split.o \

scripts/checkpatch.pl

@@ -7062,12 +7062,6 @@ sub process {
 			}
 		}
 
-# check for mutex_trylock_recursive usage
-		if ($line =~ /mutex_trylock_recursive/) {
-			ERROR("LOCKING",
-			      "recursive locking is bad, do not use this ever.\n" . $herecurr);
-		}
-
 # check for lockdep_set_novalidate_class
 		if ($line =~ /^.\s*lockdep_set_novalidate_class\s*\(/ ||
 		    $line =~ /__lockdep_no_validate__\s*\)/ ) {

tools/memory-model/Documentation/glossary.txt

@@ -33,10 +33,11 @@ Acquire:  With respect to a lock, acquiring that lock, for example,
 	acquire loads.
 
 	When an acquire load returns the value stored by a release store
-	to that same variable, then all operations preceding that store
-	happen before any operations following that load acquire.
+	to that same variable, (in other words, the acquire load "reads
+	from" the release store), then all operations preceding that
+	store "happen before" any operations following that load acquire.
 
-	See also "Relaxed" and "Release".
+	See also "Happens-Before", "Reads-From", "Relaxed", and "Release".
 
 Coherence (co):  When one CPU's store to a given variable overwrites
 	either the value from another CPU's store or some later value,
@@ -119,6 +120,11 @@ Fully Ordered:  An operation such as smp_mb() that orders all of
 	that orders all of its CPU's prior accesses, itself, and
 	all of its CPU's subsequent accesses.
 
+Happens-Before (hb): A relation between two accesses in which LKMM
+	guarantees the first access precedes the second.  For more
+	detail, please see the "THE HAPPENS-BEFORE RELATION: hb"
+	section of explanation.txt.
+
 Marked Access:  An access to a variable that uses an special function or
 	macro such as "r1 = READ_ONCE(x)" or "smp_store_release(&a, 1)".
 

tools/memory-model/README

@@ -51,7 +51,7 @@ klitmus7 Compatibility Table
 	============  ==========
 	target Linux  herdtools7
 	------------  ----------
-	     -- 4.18  7.48 --
+	     -- 4.14  7.48 --
 	4.15 -- 4.19  7.49 --
 	4.20 -- 5.5   7.54 --
 	5.6  --       7.56 --

tools/memory-model/litmus-tests/CoRR+poonceonce+Once.litmus

@@ -7,9 +7,7 @@ C CoRR+poonceonce+Once
  * reads from the same variable are ordered.
  *)
 
-{
-	int x;
-}
+{}
 
 P0(int *x)
 {

tools/memory-model/litmus-tests/CoRW+poonceonce+Once.litmus

@@ -7,9 +7,7 @@ C CoRW+poonceonce+Once
  * a given variable and a later write to that same variable are ordered.
  *)
 
-{
-	int x;
-}
+{}
 
 P0(int *x)
 {

tools/memory-model/litmus-tests/CoWR+poonceonce+Once.litmus

@@ -7,9 +7,7 @@ C CoWR+poonceonce+Once
  * given variable and a later read from that same variable are ordered.
  *)
 
-{
-	int x;
-}
+{}
 
 P0(int *x)
 {

tools/memory-model/litmus-tests/CoWW+poonceonce.litmus

@@ -7,9 +7,7 @@ C CoWW+poonceonce
  * writes to the same variable are ordered.
  *)
 
-{
-	int x;
-}
+{}
 
 P0(int *x)
 {

tools/memory-model/litmus-tests/IRIW+fencembonceonces+OnceOnce.litmus

@@ -10,10 +10,7 @@ C IRIW+fencembonceonces+OnceOnce
  * process?  This litmus test exercises LKMM's "propagation" rule.
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x)
 {

tools/memory-model/litmus-tests/IRIW+poonceonces+OnceOnce.litmus

@@ -10,10 +10,7 @@ C IRIW+poonceonces+OnceOnce
  * different process?
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x)
 {

tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus

@@ -7,12 +7,7 @@ C ISA2+pooncelock+pooncelock+pombonce
  * (in P0() and P1()) is visible to external process P2().
  *)
 
-{
-	spinlock_t mylock;
-	int x;
-	int y;
-	int z;
-}
+{}
 
 P0(int *x, int *y, spinlock_t *mylock)
 {

tools/memory-model/litmus-tests/ISA2+poonceonces.litmus

@@ -9,11 +9,7 @@ C ISA2+poonceonces
  * of the smp_load_acquire() invocations are replaced by READ_ONCE()?
  *)
 
-{
-	int x;
-	int y;
-	int z;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/ISA2+pooncerelease+poacquirerelease+poacquireonce.litmus

@@ -11,11 +11,7 @@ C ISA2+pooncerelease+poacquirerelease+poacquireonce
  * (AKA non-rf) link, so release-acquire is all that is needed.
  *)
 
-{
-	int x;
-	int y;
-	int z;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/LB+fencembonceonce+ctrlonceonce.litmus

@@ -11,10 +11,7 @@ C LB+fencembonceonce+ctrlonceonce
  * another control dependency and order would still be maintained.)
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/LB+poacquireonce+pooncerelease.litmus

@@ -8,10 +8,7 @@ C LB+poacquireonce+pooncerelease
  * to the other?
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/LB+poonceonces.litmus

@@ -7,10 +7,7 @@ C LB+poonceonces
  * be prevented even with no explicit ordering?
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/MP+fencewmbonceonce+fencermbonceonce.litmus

@@ -8,10 +8,7 @@ C MP+fencewmbonceonce+fencermbonceonce
  * is usually better to use smp_store_release() and smp_load_acquire().
  *)
 
-{
-	int buf;
-	int flag;
-}
+{}
 
 P0(int *buf, int *flag) // Producer
 {

tools/memory-model/litmus-tests/MP+onceassign+derefonce.litmus

@@ -10,9 +10,7 @@ C MP+onceassign+derefonce
  *)
 
 {
-	int *p=y;
-	int x;
-	int y=0;
+p=y;
 }
 
 P0(int *x, int **p) // Producer

tools/memory-model/litmus-tests/MP+polockmbonce+poacquiresilsil.litmus

@@ -10,10 +10,7 @@ C MP+polockmbonce+poacquiresilsil
  * executed before the lock was acquired (loosely speaking).
  *)
 
-{
-	spinlock_t lo;
-	int x;
-}
+{}
 
 P0(spinlock_t *lo, int *x) // Producer
 {

tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus

@@ -10,10 +10,7 @@ C MP+polockonce+poacquiresilsil
  * speaking).
  *)
 
-{
-	spinlock_t lo;
-	int x;
-}
+{}
 
 P0(spinlock_t *lo, int *x) // Producer
 {

tools/memory-model/litmus-tests/MP+polocks.litmus

@@ -11,11 +11,7 @@ C MP+polocks
  * to see all prior accesses by those other CPUs.
  *)
 
-{
-	spinlock_t mylock;
-	int buf;
-	int flag;
-}
+{}
 
 P0(int *buf, int *flag, spinlock_t *mylock) // Producer
 {

tools/memory-model/litmus-tests/MP+poonceonces.litmus

@@ -7,10 +7,7 @@ C MP+poonceonces
  * no ordering at all?
  *)
 
-{
-	int buf;
-	int flag;
-}
+{}
 
 P0(int *buf, int *flag) // Producer
 {

tools/memory-model/litmus-tests/MP+pooncerelease+poacquireonce.litmus

@@ -8,10 +8,7 @@ C MP+pooncerelease+poacquireonce
  * pattern.
  *)
 
-{
-	int buf;
-	int flag;
-}
+{}
 
 P0(int *buf, int *flag) // Producer
 {

tools/memory-model/litmus-tests/MP+porevlocks.litmus

@@ -11,11 +11,7 @@ C MP+porevlocks
  * see all prior accesses by those other CPUs.
  *)
 
-{
-	spinlock_t mylock;
-	int buf;
-	int flag;
-}
+{}
 
 P0(int *buf, int *flag, spinlock_t *mylock) // Consumer
 {

tools/memory-model/litmus-tests/R+fencembonceonces.litmus

@@ -9,10 +9,7 @@ C R+fencembonceonces
  * cause the resulting test to be allowed.
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/R+poonceonces.litmus

@@ -8,10 +8,7 @@ C R+poonceonces
  * store propagation delays.
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/S+fencewmbonceonce+poacquireonce.litmus

@@ -7,10 +7,7 @@ C S+fencewmbonceonce+poacquireonce
  * store against a subsequent store?
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/S+poonceonces.litmus

@@ -9,10 +9,7 @@ C S+poonceonces
  * READ_ONCE(), is ordering preserved?
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/SB+fencembonceonces.litmus

@@ -9,10 +9,7 @@ C SB+fencembonceonces
  * suffice, but not much else.)
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/SB+poonceonces.litmus

@@ -8,10 +8,7 @@ C SB+poonceonces
  * variable that the preceding process reads.
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/SB+rfionceonce-poonceonces.litmus

@@ -6,10 +6,7 @@ C SB+rfionceonce-poonceonces
  * This litmus test demonstrates that LKMM is not fully multicopy atomic.
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x, int *y)
 {

tools/memory-model/litmus-tests/WRC+poonceonces+Once.litmus

@@ -8,10 +8,7 @@ C WRC+poonceonces+Once
  * test has no ordering at all.
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x)
 {

tools/memory-model/litmus-tests/WRC+pooncerelease+fencermbonceonce+Once.litmus

@@ -10,10 +10,7 @@ C WRC+pooncerelease+fencermbonceonce+Once
  * is A-cumulative in LKMM.
  *)
 
-{
-	int x;
-	int y;
-}
+{}
 
 P0(int *x)
 {

tools/memory-model/litmus-tests/Z6.0+pooncelock+poonceLock+pombonce.litmus

@@ -9,12 +9,7 @@ C Z6.0+pooncelock+poonceLock+pombonce
  * by CPUs not holding that lock.
  *)
 
-{
-	spinlock_t mylock;
-	int x;
-	int y;
-	int z;
-}
+{}
 
 P0(int *x, int *y, spinlock_t *mylock)
 {

tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus

@@ -8,12 +8,7 @@ C Z6.0+pooncelock+pooncelock+pombonce
  * seen as ordered by a third process not holding that lock.
  *)
 
-{
-	spinlock_t mylock;
-	int x;
-	int y;
-	int z;
-}
+{}
 
 P0(int *x, int *y, spinlock_t *mylock)
 {

tools/memory-model/litmus-tests/Z6.0+pooncerelease+poacquirerelease+fencembonceonce.litmus

@@ -14,11 +14,7 @@ C Z6.0+pooncerelease+poacquirerelease+fencembonceonce
  * involving locking.)
  *)
 
-{
-	int x;
-	int y;
-	int z;
-}
+{}
 
 P0(int *x, int *y)
 {