locking: Move mcs_spinlock.h into kernel/locking/

The mcs_spinlock code is not meant (or suitable) as a generic locking
primitive, therefore take it away from the normal includes and place
it in kernel/locking/.

This way the locking primitives implemented there can use it as part
of their implementation but we do not risk it getting used
inapropriately.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-byirmpamgr7h25m5kyavwpzx@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 114 deletions

diff --git a/include/linux/mcs_spinlock.h b/include/linux/mcs_spinlock.h
deleted file mode 100644
index f2a5c6360083..000000000000
--- a/include/linux/mcs_spinlock.h
+++ /dev/null
@@ -1,114 +0,0 @@
-/*
- * MCS lock defines
- *
- * This file contains the main data structure and API definitions of MCS lock.
- *
- * The MCS lock (proposed by Mellor-Crummey and Scott) is a simple spin-lock
- * with the desirable properties of being fair, and with each cpu trying
- * to acquire the lock spinning on a local variable.
- * It avoids expensive cache bouncings that common test-and-set spin-lock
- * implementations incur.
- */
-#ifndef __LINUX_MCS_SPINLOCK_H
-#define __LINUX_MCS_SPINLOCK_H
-
-#include <asm/mcs_spinlock.h>
-
-struct mcs_spinlock {
-	struct mcs_spinlock *next;
-	int locked; /* 1 if lock acquired */
-};
-
-#ifndef arch_mcs_spin_lock_contended
-/*
- * Using smp_load_acquire() provides a memory barrier that ensures
- * subsequent operations happen after the lock is acquired.
- */
-#define arch_mcs_spin_lock_contended(l)					\
-do {									\
-	while (!(smp_load_acquire(l)))					\
-		arch_mutex_cpu_relax();					\
-} while (0)
-#endif
-
-#ifndef arch_mcs_spin_unlock_contended
-/*
- * smp_store_release() provides a memory barrier to ensure all
- * operations in the critical section has been completed before
- * unlocking.
- */
-#define arch_mcs_spin_unlock_contended(l)				\
-	smp_store_release((l), 1)
-#endif
-
-/*
- * Note: the smp_load_acquire/smp_store_release pair is not
- * sufficient to form a full memory barrier across
- * cpus for many architectures (except x86) for mcs_unlock and mcs_lock.
- * For applications that need a full barrier across multiple cpus
- * with mcs_unlock and mcs_lock pair, smp_mb__after_unlock_lock() should be
- * used after mcs_lock.
- */
-
-/*
- * In order to acquire the lock, the caller should declare a local node and
- * pass a reference of the node to this function in addition to the lock.
- * If the lock has already been acquired, then this will proceed to spin
- * on this node->locked until the previous lock holder sets the node->locked
- * in mcs_spin_unlock().
- *
- * We don't inline mcs_spin_lock() so that perf can correctly account for the
- * time spent in this lock function.
- */
-static inline
-void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
-{
-	struct mcs_spinlock *prev;
-
-	/* Init node */
-	node->locked = 0;
-	node->next   = NULL;
-
-	prev = xchg(lock, node);
-	if (likely(prev == NULL)) {
-		/*
-		 * Lock acquired, don't need to set node->locked to 1. Threads
-		 * only spin on its own node->locked value for lock acquisition.
-		 * However, since this thread can immediately acquire the lock
-		 * and does not proceed to spin on its own node->locked, this
-		 * value won't be used. If a debug mode is needed to
-		 * audit lock status, then set node->locked value here.
-		 */
-		return;
-	}
-	ACCESS_ONCE(prev->next) = node;
-
-	/* Wait until the lock holder passes the lock down. */
-	arch_mcs_spin_lock_contended(&node->locked);
-}
-
-/*
- * Releases the lock. The caller should pass in the corresponding node that
- * was used to acquire the lock.
- */
-static inline
-void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
-{
-	struct mcs_spinlock *next = ACCESS_ONCE(node->next);
-
-	if (likely(!next)) {
-		/*
-		 * Release the lock by setting it to NULL
-		 */
-		if (likely(cmpxchg(lock, node, NULL) == node))
-			return;
-		/* Wait until the next pointer is set */
-		while (!(next = ACCESS_ONCE(node->next)))
-			arch_mutex_cpu_relax();
-	}
-
-	/* Pass lock to next waiter. */
-	arch_mcs_spin_unlock_contended(&next->locked);
-}
-
-#endif /* __LINUX_MCS_SPINLOCK_H */