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Subject[PATCH v9 5/5] qrwlock: Use the mcs_spinlock helper functions for MCS queuing
Date
There is a pending MCS lock patch series that adds generic MCS lock
helper functions to do MCS-style locking. This patch will enable
the queue rwlock to use that generic MCS lock/unlock primitives for
internal queuing. This patch should only be merged after the merging
of that generic MCS locking patch.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/asm-generic/qrwlock.h | 7 +---
kernel/locking/qrwlock.c | 71 ++++-------------------------------------
2 files changed, 9 insertions(+), 69 deletions(-)

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 68f488b..db6b1e2 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -38,10 +38,7 @@
* the writer field. The least significant 8 bits is the writer field
* whereas the remaining 24 bits is the reader count.
*/
-struct qrwnode {
- struct qrwnode *next;
- int wait; /* Waiting flag */
-};
+struct mcs_spinlock;

typedef struct qrwlock {
union qrwcnts {
@@ -57,7 +54,7 @@ typedef struct qrwlock {
atomic_t rwa; /* Reader/writer atomic */
u32 rwc; /* Reader/writer counts */
} cnts;
- struct qrwnode *waitq; /* Tail of waiting queue */
+ struct mcs_spinlock *waitq; /* Tail of waiting queue */
} arch_rwlock_t;

/*
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index 2727188..18b4f2c 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -20,6 +20,7 @@
#include <linux/cpumask.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
+#include <linux/mcs_spinlock.h>
#include <asm-generic/qrwlock.h>

/*
@@ -58,64 +59,6 @@
#endif

/**
- * wait_in_queue - Add to queue and wait until it is at the head
- * @lock: Pointer to queue rwlock structure
- * @node: Node pointer to be added to the queue
- */
-static inline void wait_in_queue(struct qrwlock *lock, struct qrwnode *node)
-{
- struct qrwnode *prev;
-
- node->next = NULL;
- node->wait = true;
- prev = xchg(&lock->waitq, node);
- if (prev) {
- prev->next = node;
- /*
- * Wait until the waiting flag is off
- */
- while (smp_load_acquire(&node->wait))
- arch_mutex_cpu_relax();
- }
-}
-
-/**
- * signal_next - Signal the next one in queue to be at the head
- * @lock: Pointer to queue rwlock structure
- * @node: Node pointer to the current head of queue
- */
-static inline void signal_next(struct qrwlock *lock, struct qrwnode *node)
-{
- struct qrwnode *next;
-
- /*
- * Try to notify the next node first without disturbing the cacheline
- * of the lock. If that fails, check to see if it is the last node
- * and so should clear the wait queue.
- */
- next = ACCESS_ONCE(node->next);
- if (likely(next))
- goto notify_next;
-
- /*
- * Clear the wait queue if it is the last node
- */
- if ((ACCESS_ONCE(lock->waitq) == node) &&
- (cmpxchg(&lock->waitq, node, NULL) == node))
- return;
- /*
- * Wait until the next one in queue set up the next field
- */
- while (likely(!(next = ACCESS_ONCE(node->next))))
- arch_mutex_cpu_relax();
- /*
- * The next one in queue is now at the head
- */
-notify_next:
- smp_store_release(&next->wait, false);
-}
-
-/**
* rspin_until_writer_unlock - inc reader count & spin until writer is gone
* @lock : Pointer to queue rwlock structure
* @writer: Current queue rwlock writer status byte
@@ -138,7 +81,7 @@ rspin_until_writer_unlock(struct qrwlock *lock, u32 rwc)
*/
void queue_read_lock_slowpath(struct qrwlock *lock)
{
- struct qrwnode node;
+ struct mcs_spinlock node;
union qrwcnts cnts;

/*
@@ -158,7 +101,7 @@ void queue_read_lock_slowpath(struct qrwlock *lock)
/*
* Put the reader into the wait queue
*/
- wait_in_queue(lock, &node);
+ mcs_spin_lock(&lock->waitq, &node);

/*
* At the head of the wait queue now, wait until the writer state
@@ -175,7 +118,7 @@ void queue_read_lock_slowpath(struct qrwlock *lock)
/*
* Signal the next one in queue to become queue head
*/
- signal_next(lock, &node);
+ mcs_spin_unlock(&lock->waitq, &node);
}
EXPORT_SYMBOL(queue_read_lock_slowpath);

@@ -231,18 +174,18 @@ static inline void queue_write_3step_lock(struct qrwlock *lock)
*/
void queue_write_lock_slowpath(struct qrwlock *lock)
{
- struct qrwnode node;
+ struct mcs_spinlock node;

/*
* Put the writer into the wait queue
*/
- wait_in_queue(lock, &node);
+ mcs_spin_lock(&lock->waitq, &node);

/*
* At the head of the wait queue now, call queue_write_3step_lock()
* to acquire the lock until it is done.
*/
queue_write_3step_lock(lock);
- signal_next(lock, &node);
+ mcs_spin_unlock(&lock->waitq, &node);
}
EXPORT_SYMBOL(queue_write_lock_slowpath);
--
1.7.1


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