[PATCH v5 2/5] locking/qspinlock: Refactor the qspinlock slow path

[Alex Kogan]

Move some of the code manipulating the spin lock into separate functions.
This would allow easier integration of alternative ways to manipulate
that lock.

Signed-off-by: Alex Kogan <alex.ko...@oracle.com>
Reviewed-by: Steve Sistare <steven.sist...@oracle.com>
---
 kernel/locking/qspinlock.c | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 804c0fbd6328..c06d1e8075d9 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -288,6 +288,34 @@ static __always_inline u32  __pv_wait_head_or_lock(struct 
qspinlock *lock,
 #define queued_spin_lock_slowpath      native_queued_spin_lock_slowpath
 #endif
 
+/*
+ * __try_clear_tail - try to clear tail by setting the lock value to
+ * _Q_LOCKED_VAL.
+ * @lock: Pointer to the queued spinlock structure
+ * @val: Current value of the lock
+ * @node: Pointer to the MCS node of the lock holder
+ */
+static __always_inline bool __try_clear_tail(struct qspinlock *lock,
+                                                  u32 val,
+                                                  struct mcs_spinlock *node)
+{
+       return atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL);
+}
+
+/*
+ * __mcs_pass_lock - pass the MCS lock to the next waiter
+ * @node: Pointer to the MCS node of the lock holder
+ * @next: Pointer to the MCS node of the first waiter in the MCS queue
+ */
+static __always_inline void __mcs_pass_lock(struct mcs_spinlock *node,
+                                           struct mcs_spinlock *next)
+{
+       arch_mcs_pass_lock(&next->locked, 1);
+}
+
+#define try_clear_tail __try_clear_tail
+#define mcs_pass_lock          __mcs_pass_lock
+
 #endif /* _GEN_PV_LOCK_SLOWPATH */
 
 /**
@@ -532,7 +560,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 
val)
         *       PENDING will make the uncontended transition fail.
         */
        if ((val & _Q_TAIL_MASK) == tail) {
-               if (atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL))
+               if (try_clear_tail(lock, val, node))
                        goto release; /* No contention */
        }
 
@@ -549,7 +577,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 
val)
        if (!next)
                next = smp_cond_load_relaxed(&node->next, (VAL));
 
-       arch_mcs_pass_lock(&next->locked, 1);
+       mcs_pass_lock(node, next);
        pv_kick_node(lock, next);
 
 release:
@@ -574,6 +602,12 @@ EXPORT_SYMBOL(queued_spin_lock_slowpath);
 #undef pv_kick_node
 #undef pv_wait_head_or_lock
 
+#undef try_clear_tail
+#define try_clear_tail         __try_clear_tail
+
+#undef mcs_pass_lock
+#define mcs_pass_lock                  __mcs_pass_lock
+
 #undef  queued_spin_lock_slowpath
 #define queued_spin_lock_slowpath      __pv_queued_spin_lock_slowpath
 
-- 
2.11.0 (Apple Git-81)