Module Name: src
Committed By: riastradh
Date: Wed Apr 13 08:43:56 UTC 2016
Modified Files:
src/sys/external/bsd/drm2/include/linux: spinlock.h
Log Message:
Provide reader/writer semantics with recursive readers.
To generate a diff of this commit:
cvs rdiff -u -r1.6 -r1.7 src/sys/external/bsd/drm2/include/linux/spinlock.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/external/bsd/drm2/include/linux/spinlock.h
diff -u src/sys/external/bsd/drm2/include/linux/spinlock.h:1.6 src/sys/external/bsd/drm2/include/linux/spinlock.h:1.7
--- src/sys/external/bsd/drm2/include/linux/spinlock.h:1.6 Thu Jan 1 01:15:42 2015
+++ src/sys/external/bsd/drm2/include/linux/spinlock.h Wed Apr 13 08:43:56 2016
@@ -1,4 +1,4 @@
-/* $NetBSD: spinlock.h,v 1.6 2015/01/01 01:15:42 mrg Exp $ */
+/* $NetBSD: spinlock.h,v 1.7 2016/04/13 08:43:56 riastradh Exp $ */
/*-
* Copyright (c) 2013 The NetBSD Foundation, Inc.
@@ -35,6 +35,8 @@
#include <sys/cdefs.h>
#include <sys/mutex.h>
+#include <machine/limits.h>
+
#define __acquires(lock) /* XXX lockdep stuff */
#define __releases(lock) /* XXX lockdep stuff */
@@ -108,18 +110,71 @@ spin_lock_destroy(spinlock_t *spinlock)
KASSERT(mutex_owned(&(spinlock)->sl_lock))
/*
- * Linux rwlocks are reader/writer spin locks. We implement them as
- * normal spin locks without reader/writer semantics for expedience.
- * If that turns out to not work, adapting to reader/writer semantics
- * shouldn't be too hard.
+ * Stupid reader/writer spin locks. No attempt to avoid writer
+ * starvation. Must allow recursive readers. We use mutex and state
+ * instead of compare-and-swap for expedience and LOCKDEBUG support.
*/
-#define rwlock_t spinlock_t
-#define rwlock_init spin_lock_init
-#define rwlock_destroy spin_lock_destroy
-#define write_lock_irq spin_lock_irq
-#define write_unlock_irq spin_unlock_irq
-#define read_lock spin_lock
-#define read_unlock spin_unlock
+typedef struct linux_rwlock {
+ kmutex_t rw_lock;
+ unsigned rw_nreaders;
+} rwlock_t;
+
+static inline void
+rwlock_init(rwlock_t *rw)
+{
+
+ mutex_init(&rw->rw_lock, MUTEX_DEFAULT, IPL_VM);
+ rw->rw_nreaders = 0;
+}
+
+static inline void
+rwlock_destroy(rwlock_t *rw)
+{
+
+ KASSERTMSG(rw->rw_nreaders == 0,
+ "rwlock still held by %u readers", rw->rw_nreaders);
+ mutex_destroy(&rw->rw_lock);
+}
+
+static inline void
+write_lock_irq(rwlock_t *rw)
+{
+
+ for (;;) {
+ mutex_spin_enter(&rw->rw_lock);
+ if (rw->rw_nreaders == 0)
+ break;
+ mutex_spin_exit(&rw->rw_lock);
+ }
+}
+
+static inline void
+write_unlock_irq(rwlock_t *rw)
+{
+
+ KASSERT(rw->rw_nreaders == 0);
+ mutex_spin_exit(&rw->rw_lock);
+}
+
+static inline void
+read_lock(rwlock_t *rw)
+{
+
+ mutex_spin_enter(&rw->rw_lock);
+ KASSERT(rw->rw_nreaders < UINT_MAX);
+ rw->rw_nreaders++;
+ mutex_spin_exit(&rw->rw_lock);
+}
+
+static inline void
+read_unlock(rwlock_t *rw)
+{
+
+ mutex_spin_enter(&rw->rw_lock);
+ KASSERT(0 < rw->rw_nreaders);
+ rw->rw_nreaders--;
+ mutex_spin_exit(&rw->rw_lock);
+}
#endif /* _LINUX_SPINLOCK_H_ */
