Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar:
 "The main changes in this cycle were:

   - rwsem micro-optimizations (Davidlohr Bueso)

   - Improve the implementation and optimize the performance of
     percpu-rwsems. (Peter Zijlstra.)

   - Convert all lglock users to better facilities such as percpu-rwsems
     or percpu-spinlocks and remove lglocks. (Peter Zijlstra)

   - Remove the ticket (spin)lock implementation. (Peter Zijlstra)

   - Korean translation of memory-barriers.txt and related fixes to the
     English document. (SeongJae Park)

   - misc fixes and cleanups"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
  x86/cmpxchg, locking/atomics: Remove superfluous definitions
  x86, locking/spinlocks: Remove ticket (spin)lock implementation
  locking/lglock: Remove lglock implementation
  stop_machine: Remove stop_cpus_lock and lg_double_lock/unlock()
  fs/locks: Use percpu_down_read_preempt_disable()
  locking/percpu-rwsem: Add down_read_preempt_disable()
  fs/locks: Replace lg_local with a per-cpu spinlock
  fs/locks: Replace lg_global with a percpu-rwsem
  locking/percpu-rwsem: Add DEFINE_STATIC_PERCPU_RWSEMand percpu_rwsem_assert_held()
  locking/pv-qspinlock: Use cmpxchg_release() in __pv_queued_spin_unlock()
  locking/rwsem, x86: Drop a bogus cc clobber
  futex: Add some more function commentry
  locking/hung_task: Show all locks
  locking/rwsem: Scan the wait_list for readers only once
  locking/rwsem: Remove a few useless comments
  locking/rwsem: Return void in __rwsem_mark_wake()
  locking, rcu, cgroup: Avoid synchronize_sched() in __cgroup_procs_write()
  locking/Documentation: Add Korean translation
  locking/Documentation: Fix a typo of example result
  locking/Documentation: Fix wrong section reference
  ...

3 files changed, 100 insertions, 90 deletions

diff --git a/include/linux/lglock.h b/include/linux/lglock.h
deleted file mode 100644
index c92ebd100d9b..000000000000
--- a/include/linux/lglock.h
+++ /dev/null
@@ -1,81 +0,0 @@
-/*
- * Specialised local-global spinlock. Can only be declared as global variables
- * to avoid overhead and keep things simple (and we don't want to start using
- * these inside dynamically allocated structures).
- *
- * "local/global locks" (lglocks) can be used to:
- *
- * - Provide fast exclusive access to per-CPU data, with exclusive access to
- *   another CPU's data allowed but possibly subject to contention, and to
- *   provide very slow exclusive access to all per-CPU data.
- * - Or to provide very fast and scalable read serialisation, and to provide
- *   very slow exclusive serialisation of data (not necessarily per-CPU data).
- *
- * Brlocks are also implemented as a short-hand notation for the latter use
- * case.
- *
- * Copyright 2009, 2010, Nick Piggin, Novell Inc.
- */
-#ifndef __LINUX_LGLOCK_H
-#define __LINUX_LGLOCK_H
-
-#include <linux/spinlock.h>
-#include <linux/lockdep.h>
-#include <linux/percpu.h>
-#include <linux/cpu.h>
-#include <linux/notifier.h>
-
-#ifdef CONFIG_SMP
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-#define LOCKDEP_INIT_MAP lockdep_init_map
-#else
-#define LOCKDEP_INIT_MAP(a, b, c, d)
-#endif
-
-struct lglock {
-	arch_spinlock_t __percpu *lock;
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-	struct lock_class_key lock_key;
-	struct lockdep_map    lock_dep_map;
-#endif
-};
-
-#define DEFINE_LGLOCK(name)						\
-	static DEFINE_PER_CPU(arch_spinlock_t, name ## _lock)		\
-	= __ARCH_SPIN_LOCK_UNLOCKED;					\
-	struct lglock name = { .lock = &name ## _lock }
-
-#define DEFINE_STATIC_LGLOCK(name)					\
-	static DEFINE_PER_CPU(arch_spinlock_t, name ## _lock)		\
-	= __ARCH_SPIN_LOCK_UNLOCKED;					\
-	static struct lglock name = { .lock = &name ## _lock }
-
-void lg_lock_init(struct lglock *lg, char *name);
-
-void lg_local_lock(struct lglock *lg);
-void lg_local_unlock(struct lglock *lg);
-void lg_local_lock_cpu(struct lglock *lg, int cpu);
-void lg_local_unlock_cpu(struct lglock *lg, int cpu);
-
-void lg_double_lock(struct lglock *lg, int cpu1, int cpu2);
-void lg_double_unlock(struct lglock *lg, int cpu1, int cpu2);
-
-void lg_global_lock(struct lglock *lg);
-void lg_global_unlock(struct lglock *lg);
-
-#else
-/* When !CONFIG_SMP, map lglock to spinlock */
-#define lglock spinlock
-#define DEFINE_LGLOCK(name) DEFINE_SPINLOCK(name)
-#define DEFINE_STATIC_LGLOCK(name) static DEFINE_SPINLOCK(name)
-#define lg_lock_init(lg, name) spin_lock_init(lg)
-#define lg_local_lock spin_lock
-#define lg_local_unlock spin_unlock
-#define lg_local_lock_cpu(lg, cpu) spin_lock(lg)
-#define lg_local_unlock_cpu(lg, cpu) spin_unlock(lg)
-#define lg_global_lock spin_lock
-#define lg_global_unlock spin_unlock
-#endif
-
-#endif
diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index c2fa3ecb0dce..5b2e6159b744 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -10,32 +10,122 @@
 
 struct percpu_rw_semaphore {
 	struct rcu_sync		rss;
-	unsigned int __percpu	*fast_read_ctr;
+	unsigned int __percpu	*read_count;
 	struct rw_semaphore	rw_sem;
-	atomic_t		slow_read_ctr;
-	wait_queue_head_t	write_waitq;
+	wait_queue_head_t	writer;
+	int			readers_block;
 };
 
-extern void percpu_down_read(struct percpu_rw_semaphore *);
-extern int  percpu_down_read_trylock(struct percpu_rw_semaphore *);
-extern void percpu_up_read(struct percpu_rw_semaphore *);
+#define DEFINE_STATIC_PERCPU_RWSEM(name)				\
+static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name);		\
+static struct percpu_rw_semaphore name = {				\
+	.rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC),	\
+	.read_count = &__percpu_rwsem_rc_##name,			\
+	.rw_sem = __RWSEM_INITIALIZER(name.rw_sem),			\
+	.writer = __WAIT_QUEUE_HEAD_INITIALIZER(name.writer),		\
+}
+
+extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
+extern void __percpu_up_read(struct percpu_rw_semaphore *);
+
+static inline void percpu_down_read_preempt_disable(struct percpu_rw_semaphore *sem)
+{
+	might_sleep();
+
+	rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 0, _RET_IP_);
+
+	preempt_disable();
+	/*
+	 * We are in an RCU-sched read-side critical section, so the writer
+	 * cannot both change sem->state from readers_fast and start checking
+	 * counters while we are here. So if we see !sem->state, we know that
+	 * the writer won't be checking until we're past the preempt_enable()
+	 * and that one the synchronize_sched() is done, the writer will see
+	 * anything we did within this RCU-sched read-size critical section.
+	 */
+	__this_cpu_inc(*sem->read_count);
+	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
+		__percpu_down_read(sem, false); /* Unconditional memory barrier */
+	barrier();
+	/*
+	 * The barrier() prevents the compiler from
+	 * bleeding the critical section out.
+	 */
+}
+
+static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
+{
+	percpu_down_read_preempt_disable(sem);
+	preempt_enable();
+}
+
+static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
+{
+	int ret = 1;
+
+	preempt_disable();
+	/*
+	 * Same as in percpu_down_read().
+	 */
+	__this_cpu_inc(*sem->read_count);
+	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
+		ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
+	preempt_enable();
+	/*
+	 * The barrier() from preempt_enable() prevents the compiler from
+	 * bleeding the critical section out.
+	 */
+
+	if (ret)
+		rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
+
+	return ret;
+}
+
+static inline void percpu_up_read_preempt_enable(struct percpu_rw_semaphore *sem)
+{
+	/*
+	 * The barrier() prevents the compiler from
+	 * bleeding the critical section out.
+	 */
+	barrier();
+	/*
+	 * Same as in percpu_down_read().
+	 */
+	if (likely(rcu_sync_is_idle(&sem->rss)))
+		__this_cpu_dec(*sem->read_count);
+	else
+		__percpu_up_read(sem); /* Unconditional memory barrier */
+	preempt_enable();
+
+	rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
+}
+
+static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
+{
+	preempt_disable();
+	percpu_up_read_preempt_enable(sem);
+}
 
 extern void percpu_down_write(struct percpu_rw_semaphore *);
 extern void percpu_up_write(struct percpu_rw_semaphore *);
 
 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
 				const char *, struct lock_class_key *);
+
 extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
 
-#define percpu_init_rwsem(brw)	\
+#define percpu_init_rwsem(sem)					\
 ({								\
 	static struct lock_class_key rwsem_key;			\
-	__percpu_init_rwsem(brw, #brw, &rwsem_key);		\
+	__percpu_init_rwsem(sem, #sem, &rwsem_key);		\
 })
 
-
 #define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
 
+#define percpu_rwsem_assert_held(sem)				\
+	lockdep_assert_held(&(sem)->rw_sem)
+
 static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
 					bool read, unsigned long ip)
 {
diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
index a63a33e6196e..ece7ed9a4a70 100644
--- a/include/linux/rcu_sync.h
+++ b/include/linux/rcu_sync.h
@@ -59,6 +59,7 @@ static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
 }
 
 extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
+extern void rcu_sync_enter_start(struct rcu_sync *);
 extern void rcu_sync_enter(struct rcu_sync *);
 extern void rcu_sync_exit(struct rcu_sync *);
 extern void rcu_sync_dtor(struct rcu_sync *);