locking/qspinlock: Merge 'struct __qspinlock' into 'struct qspinlock'

'struct __qspinlock' provides a handy union of fields so that
subcomponents of the lockword can be accessed by name, without having to
manage shifts and masks explicitly and take endianness into account.

This is useful in qspinlock.h and also potentially in arch headers, so
move the 'struct __qspinlock' into 'struct qspinlock' and kill the extra
definition.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-3-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/qspinlock.h

@@ -16,7 +16,7 @@
  */
 static inline void native_queued_spin_unlock(struct qspinlock *lock)
 {
-	smp_store_release((u8 *)lock, 0);
+	smp_store_release(&lock->locked, 0);
 }
 
 #ifdef CONFIG_PARAVIRT_SPINLOCKS

arch/x86/include/asm/qspinlock_paravirt.h

@@ -22,8 +22,7 @@ PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath);
  *
  * void __pv_queued_spin_unlock(struct qspinlock *lock)
  * {
- *	struct __qspinlock *l = (void *)lock;
- *	u8 lockval = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
+ *	u8 lockval = cmpxchg(&lock->locked, _Q_LOCKED_VAL, 0);
  *
  *	if (likely(lockval == _Q_LOCKED_VAL))
  *		return;

include/asm-generic/qspinlock_types.h

@@ -29,13 +29,41 @@
 #endif
 
 typedef struct qspinlock {
-	atomic_t	val;
+	union {
+		atomic_t val;
+
+		/*
+		 * By using the whole 2nd least significant byte for the
+		 * pending bit, we can allow better optimization of the lock
+		 * acquisition for the pending bit holder.
+		 */
+#ifdef __LITTLE_ENDIAN
+		struct {
+			u8	locked;
+			u8	pending;
+		};
+		struct {
+			u16	locked_pending;
+			u16	tail;
+		};
+#else
+		struct {
+			u16	tail;
+			u16	locked_pending;
+		};
+		struct {
+			u8	reserved[2];
+			u8	pending;
+			u8	locked;
+		};
+#endif
+	};
 } arch_spinlock_t;
 
 /*
  * Initializier
  */
-#define	__ARCH_SPIN_LOCK_UNLOCKED	{ ATOMIC_INIT(0) }
+#define	__ARCH_SPIN_LOCK_UNLOCKED	{ .val = ATOMIC_INIT(0) }
 
 /*
  * Bitfields in the atomic value:

kernel/locking/qspinlock.c

@@ -114,40 +114,6 @@ static inline __pure struct mcs_spinlock *decode_tail(u32 tail)
 
 #define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK)
 
-/*
- * By using the whole 2nd least significant byte for the pending bit, we
- * can allow better optimization of the lock acquisition for the pending
- * bit holder.
- *
- * This internal structure is also used by the set_locked function which
- * is not restricted to _Q_PENDING_BITS == 8.
- */
-struct __qspinlock {
-	union {
-		atomic_t val;
-#ifdef __LITTLE_ENDIAN
-		struct {
-			u8	locked;
-			u8	pending;
-		};
-		struct {
-			u16	locked_pending;
-			u16	tail;
-		};
-#else
-		struct {
-			u16	tail;
-			u16	locked_pending;
-		};
-		struct {
-			u8	reserved[2];
-			u8	pending;
-			u8	locked;
-		};
-#endif
-	};
-};
-
 #if _Q_PENDING_BITS == 8
 /**
  * clear_pending_set_locked - take ownership and clear the pending bit.
@@ -159,9 +125,7 @@ struct __qspinlock {
  */
 static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
 {
-	struct __qspinlock *l = (void *)lock;
-
-	WRITE_ONCE(l->locked_pending, _Q_LOCKED_VAL);
+	WRITE_ONCE(lock->locked_pending, _Q_LOCKED_VAL);
 }
 
 /*
@@ -176,13 +140,11 @@ static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
  */
 static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
 {
-	struct __qspinlock *l = (void *)lock;
-
 	/*
 	 * Use release semantics to make sure that the MCS node is properly
 	 * initialized before changing the tail code.
 	 */
-	return (u32)xchg_release(&l->tail,
+	return (u32)xchg_release(&lock->tail,
 				 tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET;
 }
 
@@ -237,9 +199,7 @@ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
  */
 static __always_inline void set_locked(struct qspinlock *lock)
 {
-	struct __qspinlock *l = (void *)lock;
-
-	WRITE_ONCE(l->locked, _Q_LOCKED_VAL);
+	WRITE_ONCE(lock->locked, _Q_LOCKED_VAL);
 }
 
 

kernel/locking/qspinlock_paravirt.h

@@ -87,8 +87,6 @@ struct pv_node {
 #define queued_spin_trylock(l)	pv_hybrid_queued_unfair_trylock(l)
 static inline bool pv_hybrid_queued_unfair_trylock(struct qspinlock *lock)
 {
-	struct __qspinlock *l = (void *)lock;
-
 	/*
 	 * Stay in unfair lock mode as long as queued mode waiters are
 	 * present in the MCS wait queue but the pending bit isn't set.
@@ -97,7 +95,7 @@ static inline bool pv_hybrid_queued_unfair_trylock(struct qspinlock *lock)
 		int val = atomic_read(&lock->val);
 
 		if (!(val & _Q_LOCKED_PENDING_MASK) &&
-		   (cmpxchg_acquire(&l->locked, 0, _Q_LOCKED_VAL) == 0)) {
+		   (cmpxchg_acquire(&lock->locked, 0, _Q_LOCKED_VAL) == 0)) {
 			qstat_inc(qstat_pv_lock_stealing, true);
 			return true;
 		}
@@ -117,16 +115,12 @@ static inline bool pv_hybrid_queued_unfair_trylock(struct qspinlock *lock)
 #if _Q_PENDING_BITS == 8
 static __always_inline void set_pending(struct qspinlock *lock)
 {
-	struct __qspinlock *l = (void *)lock;
-
-	WRITE_ONCE(l->pending, 1);
+	WRITE_ONCE(lock->pending, 1);
 }
 
 static __always_inline void clear_pending(struct qspinlock *lock)
 {
-	struct __qspinlock *l = (void *)lock;
-
-	WRITE_ONCE(l->pending, 0);
+	WRITE_ONCE(lock->pending, 0);
 }
 
 /*
@@ -136,10 +130,8 @@ static __always_inline void clear_pending(struct qspinlock *lock)
  */
 static __always_inline int trylock_clear_pending(struct qspinlock *lock)
 {
-	struct __qspinlock *l = (void *)lock;
-
-	return !READ_ONCE(l->locked) &&
-	       (cmpxchg_acquire(&l->locked_pending, _Q_PENDING_VAL,
+	return !READ_ONCE(lock->locked) &&
+	       (cmpxchg_acquire(&lock->locked_pending, _Q_PENDING_VAL,
 				_Q_LOCKED_VAL) == _Q_PENDING_VAL);
 }
 #else /* _Q_PENDING_BITS == 8 */
@@ -384,7 +376,6 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
 static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
 {
 	struct pv_node *pn = (struct pv_node *)node;
-	struct __qspinlock *l = (void *)lock;
 
 	/*
 	 * If the vCPU is indeed halted, advance its state to match that of
@@ -413,7 +404,7 @@ static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
 	 * the hash table later on at unlock time, no atomic instruction is
 	 * needed.
 	 */
-	WRITE_ONCE(l->locked, _Q_SLOW_VAL);
+	WRITE_ONCE(lock->locked, _Q_SLOW_VAL);
 	(void)pv_hash(lock, pn);
 }
 
@@ -428,7 +419,6 @@ static u32
 pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
 {
 	struct pv_node *pn = (struct pv_node *)node;
-	struct __qspinlock *l = (void *)lock;
 	struct qspinlock **lp = NULL;
 	int waitcnt = 0;
 	int loop;
@@ -479,13 +469,13 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
 			 *
 			 * Matches the smp_rmb() in __pv_queued_spin_unlock().
 			 */
-			if (xchg(&l->locked, _Q_SLOW_VAL) == 0) {
+			if (xchg(&lock->locked, _Q_SLOW_VAL) == 0) {
 				/*
 				 * The lock was free and now we own the lock.
 				 * Change the lock value back to _Q_LOCKED_VAL
 				 * and unhash the table.
 				 */
-				WRITE_ONCE(l->locked, _Q_LOCKED_VAL);
+				WRITE_ONCE(lock->locked, _Q_LOCKED_VAL);
 				WRITE_ONCE(*lp, NULL);
 				goto gotlock;
 			}
@@ -493,7 +483,7 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
 		WRITE_ONCE(pn->state, vcpu_hashed);
 		qstat_inc(qstat_pv_wait_head, true);
 		qstat_inc(qstat_pv_wait_again, waitcnt);
-		pv_wait(&l->locked, _Q_SLOW_VAL);
+		pv_wait(&lock->locked, _Q_SLOW_VAL);
 
 		/*
 		 * Because of lock stealing, the queue head vCPU may not be
@@ -518,7 +508,6 @@ gotlock:
 __visible void
 __pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
 {
-	struct __qspinlock *l = (void *)lock;
 	struct pv_node *node;
 
 	if (unlikely(locked != _Q_SLOW_VAL)) {
@@ -547,7 +536,7 @@ __pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
 	 * Now that we have a reference to the (likely) blocked pv_node,
 	 * release the lock.
 	 */
-	smp_store_release(&l->locked, 0);
+	smp_store_release(&lock->locked, 0);
 
 	/*
 	 * At this point the memory pointed at by lock can be freed/reused,
@@ -573,7 +562,6 @@ __pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
 #ifndef __pv_queued_spin_unlock
 __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
 {
-	struct __qspinlock *l = (void *)lock;
 	u8 locked;
 
 	/*
@@ -581,7 +569,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
 	 * unhash. Otherwise it would be possible to have multiple @lock
 	 * entries, which would be BAD.
 	 */
-	locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0);
+	locked = cmpxchg_release(&lock->locked, _Q_LOCKED_VAL, 0);
 	if (likely(locked == _Q_LOCKED_VAL))
 		return;