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Diffstat (limited to 'kernel/locking/qrwlock.c')
-rw-r--r--kernel/locking/qrwlock.c30
1 files changed, 25 insertions, 5 deletions
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index f956ede7f90d..6c5da483966b 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -1,5 +1,5 @@
/*
- * Queue read/write lock
+ * Queued read/write locks
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -22,6 +22,26 @@
#include <linux/hardirq.h>
#include <asm/qrwlock.h>
+/*
+ * This internal data structure is used for optimizing access to some of
+ * the subfields within the atomic_t cnts.
+ */
+struct __qrwlock {
+ union {
+ atomic_t cnts;
+ struct {
+#ifdef __LITTLE_ENDIAN
+ u8 wmode; /* Writer mode */
+ u8 rcnts[3]; /* Reader counts */
+#else
+ u8 rcnts[3]; /* Reader counts */
+ u8 wmode; /* Writer mode */
+#endif
+ };
+ };
+ arch_spinlock_t lock;
+};
+
/**
* rspin_until_writer_unlock - inc reader count & spin until writer is gone
* @lock : Pointer to queue rwlock structure
@@ -107,10 +127,10 @@ void queue_write_lock_slowpath(struct qrwlock *lock)
* or wait for a previous writer to go away.
*/
for (;;) {
- cnts = atomic_read(&lock->cnts);
- if (!(cnts & _QW_WMASK) &&
- (atomic_cmpxchg(&lock->cnts, cnts,
- cnts | _QW_WAITING) == cnts))
+ struct __qrwlock *l = (struct __qrwlock *)lock;
+
+ if (!READ_ONCE(l->wmode) &&
+ (cmpxchg(&l->wmode, 0, _QW_WAITING) == 0))
break;
cpu_relax_lowlatency();