If unfair lock is supported, the lock acquisition loop at the end of
the queue_spin_lock_slowpath() function may need to detect the fact
the lock can be stolen. Code are added for the stolen lock detection.
A new qhead macro is also defined as a shorthand for mcs.locked.
Signed-off-by: Waiman Long <waiman.l...@hp.com>
---
kernel/locking/qspinlock.c | 26 +++++++++++++++++++-------
1 files changed, 19 insertions(+), 7 deletions(-)
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index e98d7d4..9e7659e 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -64,6 +64,7 @@
struct qnode {
struct mcs_spinlock mcs;
};
+#define qhead mcs.locked /* The queue head flag */
/*
* Per-CPU queue node structures; we can never have more than 4 nested
@@ -216,18 +217,20 @@ xchg_tail(struct qspinlock *lock, u32 tail, u32 *pval)
/**
* get_qlock - Set the lock bit and own the lock
- * @lock: Pointer to queue spinlock structure
+ * @lock : Pointer to queue spinlock structure
+ * Return: 1 if lock acquired, 0 otherwise
*
* This routine should only be called when the caller is the only one
* entitled to acquire the lock.
*/
-static __always_inline void get_qlock(struct qspinlock *lock)
+static __always_inline int get_qlock(struct qspinlock *lock)
{
struct __qspinlock *l = (void *)lock;
barrier();
ACCESS_ONCE(l->locked) = _Q_LOCKED_VAL;
barrier();
+ return 1;
}
/**
@@ -365,7 +368,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32
val)
tail = encode_tail(smp_processor_id(), idx);
node += idx;
- node->mcs.locked = 0;
+ node->qhead = 0;
node->mcs.next = NULL;
/*
@@ -391,7 +394,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32
val)
prev = decode_tail(old);
ACCESS_ONCE(prev->mcs.next) = (struct mcs_spinlock *)node;
- while (!smp_load_acquire(&node->mcs.locked))
+ while (!smp_load_acquire(&node->qhead))
arch_mutex_cpu_relax();
}
@@ -403,6 +406,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32
val)
*
* *,x,y -> *,0,0
*/
+retry_queue_wait:
while ((val = smp_load_acquire(&lock->val.counter))
& _Q_LOCKED_PENDING_MASK)
arch_mutex_cpu_relax();
@@ -419,12 +423,20 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32
val)
*/
for (;;) {
if (val != tail) {
- get_qlock(lock);
- break;
+ /*
+ * The get_qlock function will only failed if the
+ * lock was stolen.
+ */
+ if (get_qlock(lock))
+ break;
+ else
+ goto retry_queue_wait;
}
old = atomic_cmpxchg(&lock->val, val, _Q_LOCKED_VAL);
if (old == val)
goto release; /* No contention */
+ else if (old & _Q_LOCKED_MASK)
+ goto retry_queue_wait;
val = old;
}
@@ -435,7 +447,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32
val)
while (!(next = (struct qnode *)ACCESS_ONCE(node->mcs.next)))
arch_mutex_cpu_relax();
- arch_mcs_spin_unlock_contended(&next->mcs.locked);
+ arch_mcs_spin_unlock_contended(&next->qhead);
release:
/*
--
1.7.1
--
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