There is a pending MCS lock patch series that adds a generic MCS
locking 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@xxxxxx>
---
include/asm-generic/qrwlock.h | 7 +--
lib/qrwlock.c | 83 +++-------------------------------------
2 files changed, 9 insertions(+), 81 deletions(-)
diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 1f68499..288fb00 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -54,10 +54,7 @@ typedef u64 __nrcpupair_t;
* QRW_READER_BIAS to the rw field to increment the reader count won't
* disturb the writer and the fair fields.
*/
-struct qrwnode {
- struct qrwnode *next;
- bool wait; /* Waiting flag */
-};
+struct mcs_spinlock;
typedef struct qrwlock {
union qrwcnts {
@@ -74,7 +71,7 @@ typedef struct qrwlock {
};
__nrcpupair_t rw; /* Reader/writer number pair */
} cnts;
- struct qrwnode *waitq; /* Tail of waiting queue */
+ struct mcs_spinlock *waitq; /* Tail of waiting queue */
} arch_rwlock_t;
/*
diff --git a/lib/qrwlock.c b/lib/qrwlock.c
index 4915dc6..3ae1359 100644
--- a/lib/qrwlock.c
+++ b/lib/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>
/*
@@ -57,76 +58,6 @@
# endif
#endif
-#ifndef smp_mb__store_release
-# ifdef CONFIG_X86
-# define smp_mb__store_release() barrier()
-# else
-# define smp_mb__store_release() smp_mb()
-# endif
-#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 __always_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 (ACCESS_ONCE(node->wait))
- arch_mutex_cpu_relax();
- smp_mb__load_acquire();
- }
-}
-
-/**
- * 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 __always_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_mb__store_release();
- ACCESS_ONCE(next->wait) = false;
-}
-
/**
* rspin_until_writer_unlock - inc reader count & spin until writer is gone
* @lock: Pointer to queue rwlock structure
@@ -150,7 +81,7 @@ rspin_until_writer_unlock(struct qrwlock *lock, union qrwcnts cnts)
*/
void queue_read_lock_slowpath(struct qrwlock *lock)
{
- struct qrwnode node;
+ struct mcs_spinlock node;
union qrwcnts cnts;
/*
@@ -170,7 +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, &node);
/*
* At the head of the wait queue now, try to increment the reader
@@ -190,7 +121,7 @@ void queue_read_lock_slowpath(struct qrwlock *lock)
* Need to have a barrier with read-acquire semantics
*/
smp_mb__load_acquire();
- signal_next(lock, &node);
+ mcs_spin_unlock(lock, &node);
}
EXPORT_SYMBOL(queue_read_lock_slowpath);
@@ -256,12 +187,12 @@ static noinline int 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, &node);
/*
* At the head of the wait queue now, call queue_write_3step_lock()
@@ -269,6 +200,6 @@ void queue_write_lock_slowpath(struct qrwlock *lock)
*/
while (!queue_write_3step_lock(lock))
arch_mutex_cpu_relax();
- signal_next(lock, &node);
+ mcs_spin_unlock(lock, &node);
}
EXPORT_SYMBOL(queue_write_lock_slowpath);
--
1.7.1
--
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