570 lines
15 KiB
Diff
570 lines
15 KiB
Diff
From: Thomas Gleixner <tglx@linutronix.de>
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Date: Thu, 12 Oct 2017 17:18:06 +0200
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Subject: rtmutex: add rwlock implementation based on rtmutex
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.1-rt3.tar.xz
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The implementation is bias-based, similar to the rwsem implementation.
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/linux/rwlock_rt.h | 119 ++++++++++++
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include/linux/rwlock_types_rt.h | 55 +++++
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kernel/locking/rwlock-rt.c | 368 ++++++++++++++++++++++++++++++++++++++++
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3 files changed, 542 insertions(+)
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create mode 100644 include/linux/rwlock_rt.h
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create mode 100644 include/linux/rwlock_types_rt.h
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create mode 100644 kernel/locking/rwlock-rt.c
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--- /dev/null
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+++ b/include/linux/rwlock_rt.h
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@@ -0,0 +1,119 @@
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+#ifndef __LINUX_RWLOCK_RT_H
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+#define __LINUX_RWLOCK_RT_H
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+
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+#ifndef __LINUX_SPINLOCK_H
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+#error Do not include directly. Use spinlock.h
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+#endif
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+
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+extern void __lockfunc rt_write_lock(rwlock_t *rwlock);
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+extern void __lockfunc rt_read_lock(rwlock_t *rwlock);
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+extern int __lockfunc rt_write_trylock(rwlock_t *rwlock);
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+extern int __lockfunc rt_read_trylock(rwlock_t *rwlock);
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+extern void __lockfunc rt_write_unlock(rwlock_t *rwlock);
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+extern void __lockfunc rt_read_unlock(rwlock_t *rwlock);
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+extern int __lockfunc rt_read_can_lock(rwlock_t *rwlock);
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+extern int __lockfunc rt_write_can_lock(rwlock_t *rwlock);
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+extern void __rt_rwlock_init(rwlock_t *rwlock, char *name, struct lock_class_key *key);
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+
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+#define read_can_lock(rwlock) rt_read_can_lock(rwlock)
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+#define write_can_lock(rwlock) rt_write_can_lock(rwlock)
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+
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+#define read_trylock(lock) __cond_lock(lock, rt_read_trylock(lock))
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+#define write_trylock(lock) __cond_lock(lock, rt_write_trylock(lock))
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+
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+static inline int __write_trylock_rt_irqsave(rwlock_t *lock, unsigned long *flags)
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+{
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+ /* XXX ARCH_IRQ_ENABLED */
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+ *flags = 0;
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+ return rt_write_trylock(lock);
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+}
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+
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+#define write_trylock_irqsave(lock, flags) \
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+ __cond_lock(lock, __write_trylock_rt_irqsave(lock, &(flags)))
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+
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+#define read_lock_irqsave(lock, flags) \
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+ do { \
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+ typecheck(unsigned long, flags); \
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+ rt_read_lock(lock); \
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+ flags = 0; \
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+ } while (0)
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+
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+#define write_lock_irqsave(lock, flags) \
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+ do { \
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+ typecheck(unsigned long, flags); \
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+ rt_write_lock(lock); \
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+ flags = 0; \
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+ } while (0)
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+
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+#define read_lock(lock) rt_read_lock(lock)
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+
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+#define read_lock_bh(lock) \
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+ do { \
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+ local_bh_disable(); \
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+ rt_read_lock(lock); \
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+ } while (0)
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+
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+#define read_lock_irq(lock) read_lock(lock)
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+
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+#define write_lock(lock) rt_write_lock(lock)
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+
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+#define write_lock_bh(lock) \
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+ do { \
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+ local_bh_disable(); \
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+ rt_write_lock(lock); \
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+ } while (0)
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+
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+#define write_lock_irq(lock) write_lock(lock)
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+
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+#define read_unlock(lock) rt_read_unlock(lock)
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+
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+#define read_unlock_bh(lock) \
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+ do { \
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+ rt_read_unlock(lock); \
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+ local_bh_enable(); \
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+ } while (0)
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+
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+#define read_unlock_irq(lock) read_unlock(lock)
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+
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+#define write_unlock(lock) rt_write_unlock(lock)
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+
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+#define write_unlock_bh(lock) \
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+ do { \
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+ rt_write_unlock(lock); \
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+ local_bh_enable(); \
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+ } while (0)
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+
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+#define write_unlock_irq(lock) write_unlock(lock)
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+
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+#define read_unlock_irqrestore(lock, flags) \
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+ do { \
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+ typecheck(unsigned long, flags); \
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+ (void) flags; \
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+ rt_read_unlock(lock); \
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+ } while (0)
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+
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+#define write_unlock_irqrestore(lock, flags) \
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+ do { \
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+ typecheck(unsigned long, flags); \
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+ (void) flags; \
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+ rt_write_unlock(lock); \
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+ } while (0)
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+
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+#define rwlock_init(rwl) \
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+do { \
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+ static struct lock_class_key __key; \
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+ \
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+ __rt_rwlock_init(rwl, #rwl, &__key); \
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+} while (0)
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+
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+/*
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+ * Internal functions made global for CPU pinning
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+ */
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+void __read_rt_lock(struct rt_rw_lock *lock);
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+int __read_rt_trylock(struct rt_rw_lock *lock);
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+void __write_rt_lock(struct rt_rw_lock *lock);
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+int __write_rt_trylock(struct rt_rw_lock *lock);
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+void __read_rt_unlock(struct rt_rw_lock *lock);
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+void __write_rt_unlock(struct rt_rw_lock *lock);
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+
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+#endif
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--- /dev/null
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+++ b/include/linux/rwlock_types_rt.h
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@@ -0,0 +1,55 @@
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+#ifndef __LINUX_RWLOCK_TYPES_RT_H
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+#define __LINUX_RWLOCK_TYPES_RT_H
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+
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+#ifndef __LINUX_SPINLOCK_TYPES_H
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+#error "Do not include directly. Include spinlock_types.h instead"
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+#endif
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+
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+#ifdef CONFIG_DEBUG_LOCK_ALLOC
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+# define RW_DEP_MAP_INIT(lockname) .dep_map = { .name = #lockname }
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+#else
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+# define RW_DEP_MAP_INIT(lockname)
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+#endif
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+
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+typedef struct rt_rw_lock rwlock_t;
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+
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+#define __RW_LOCK_UNLOCKED(name) __RWLOCK_RT_INITIALIZER(name)
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+
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+#define DEFINE_RWLOCK(name) \
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+ rwlock_t name = __RW_LOCK_UNLOCKED(name)
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+
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+/*
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+ * A reader biased implementation primarily for CPU pinning.
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+ *
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+ * Can be selected as general replacement for the single reader RT rwlock
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+ * variant
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+ */
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+struct rt_rw_lock {
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+ struct rt_mutex rtmutex;
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+ atomic_t readers;
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+#ifdef CONFIG_DEBUG_LOCK_ALLOC
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+ struct lockdep_map dep_map;
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+#endif
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+};
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+
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+#define READER_BIAS (1U << 31)
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+#define WRITER_BIAS (1U << 30)
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+
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+#define __RWLOCK_RT_INITIALIZER(name) \
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+{ \
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+ .readers = ATOMIC_INIT(READER_BIAS), \
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+ .rtmutex = __RT_MUTEX_INITIALIZER_SAVE_STATE(name.rtmutex), \
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+ RW_DEP_MAP_INIT(name) \
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+}
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+
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+void __rwlock_biased_rt_init(struct rt_rw_lock *lock, const char *name,
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+ struct lock_class_key *key);
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+
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+#define rwlock_biased_rt_init(rwlock) \
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+ do { \
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+ static struct lock_class_key __key; \
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+ \
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+ __rwlock_biased_rt_init((rwlock), #rwlock, &__key); \
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+ } while (0)
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+
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+#endif
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--- /dev/null
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+++ b/kernel/locking/rwlock-rt.c
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@@ -0,0 +1,368 @@
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+/*
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+ */
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+#include <linux/sched/debug.h>
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+#include <linux/export.h>
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+
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+#include "rtmutex_common.h"
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+#include <linux/rwlock_types_rt.h>
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+
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+/*
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+ * RT-specific reader/writer locks
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+ *
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+ * write_lock()
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+ * 1) Lock lock->rtmutex
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+ * 2) Remove the reader BIAS to force readers into the slow path
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+ * 3) Wait until all readers have left the critical region
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+ * 4) Mark it write locked
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+ *
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+ * write_unlock()
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+ * 1) Remove the write locked marker
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+ * 2) Set the reader BIAS so readers can use the fast path again
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+ * 3) Unlock lock->rtmutex to release blocked readers
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+ *
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+ * read_lock()
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+ * 1) Try fast path acquisition (reader BIAS is set)
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+ * 2) Take lock->rtmutex.wait_lock which protects the writelocked flag
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+ * 3) If !writelocked, acquire it for read
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+ * 4) If writelocked, block on lock->rtmutex
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+ * 5) unlock lock->rtmutex, goto 1)
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+ *
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+ * read_unlock()
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+ * 1) Try fast path release (reader count != 1)
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+ * 2) Wake the writer waiting in write_lock()#3
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+ *
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+ * read_lock()#3 has the consequence, that rw locks on RT are not writer
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+ * fair, but writers, which should be avoided in RT tasks (think tasklist
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+ * lock), are subject to the rtmutex priority/DL inheritance mechanism.
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+ *
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+ * It's possible to make the rw locks writer fair by keeping a list of
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+ * active readers. A blocked writer would force all newly incoming readers
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+ * to block on the rtmutex, but the rtmutex would have to be proxy locked
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+ * for one reader after the other. We can't use multi-reader inheritance
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+ * because there is no way to support that with
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+ * SCHED_DEADLINE. Implementing the one by one reader boosting/handover
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+ * mechanism is a major surgery for a very dubious value.
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+ *
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+ * The risk of writer starvation is there, but the pathological use cases
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+ * which trigger it are not necessarily the typical RT workloads.
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+ */
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+
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+void __rwlock_biased_rt_init(struct rt_rw_lock *lock, const char *name,
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+ struct lock_class_key *key)
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+{
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+#ifdef CONFIG_DEBUG_LOCK_ALLOC
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+ /*
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+ * Make sure we are not reinitializing a held semaphore:
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+ */
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+ debug_check_no_locks_freed((void *)lock, sizeof(*lock));
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+ lockdep_init_map(&lock->dep_map, name, key, 0);
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+#endif
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+ atomic_set(&lock->readers, READER_BIAS);
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+ rt_mutex_init(&lock->rtmutex);
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+ lock->rtmutex.save_state = 1;
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+}
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+
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+int __read_rt_trylock(struct rt_rw_lock *lock)
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+{
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+ int r, old;
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+
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+ /*
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+ * Increment reader count, if lock->readers < 0, i.e. READER_BIAS is
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+ * set.
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+ */
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+ for (r = atomic_read(&lock->readers); r < 0;) {
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+ old = atomic_cmpxchg(&lock->readers, r, r + 1);
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+ if (likely(old == r))
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+ return 1;
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+ r = old;
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+ }
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+ return 0;
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+}
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+
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+void __sched __read_rt_lock(struct rt_rw_lock *lock)
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+{
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+ struct rt_mutex *m = &lock->rtmutex;
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+ struct rt_mutex_waiter waiter;
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+ unsigned long flags;
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+
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+ if (__read_rt_trylock(lock))
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+ return;
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+
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+ raw_spin_lock_irqsave(&m->wait_lock, flags);
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+ /*
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+ * Allow readers as long as the writer has not completely
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+ * acquired the semaphore for write.
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+ */
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+ if (atomic_read(&lock->readers) != WRITER_BIAS) {
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+ atomic_inc(&lock->readers);
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+ raw_spin_unlock_irqrestore(&m->wait_lock, flags);
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+ return;
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+ }
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+
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+ /*
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+ * Call into the slow lock path with the rtmutex->wait_lock
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+ * held, so this can't result in the following race:
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+ *
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+ * Reader1 Reader2 Writer
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+ * read_lock()
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+ * write_lock()
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+ * rtmutex_lock(m)
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+ * swait()
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+ * read_lock()
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+ * unlock(m->wait_lock)
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+ * read_unlock()
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+ * swake()
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+ * lock(m->wait_lock)
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+ * lock->writelocked=true
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+ * unlock(m->wait_lock)
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+ *
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+ * write_unlock()
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+ * lock->writelocked=false
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+ * rtmutex_unlock(m)
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+ * read_lock()
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+ * write_lock()
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+ * rtmutex_lock(m)
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+ * swait()
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+ * rtmutex_lock(m)
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+ *
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+ * That would put Reader1 behind the writer waiting on
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+ * Reader2 to call read_unlock() which might be unbound.
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+ */
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+ rt_mutex_init_waiter(&waiter, false);
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+ rt_spin_lock_slowlock_locked(m, &waiter, flags);
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+ /*
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+ * The slowlock() above is guaranteed to return with the rtmutex is
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+ * now held, so there can't be a writer active. Increment the reader
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+ * count and immediately drop the rtmutex again.
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+ */
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+ atomic_inc(&lock->readers);
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+ raw_spin_unlock_irqrestore(&m->wait_lock, flags);
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+ rt_spin_lock_slowunlock(m);
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+
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+ debug_rt_mutex_free_waiter(&waiter);
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+}
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+
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+void __read_rt_unlock(struct rt_rw_lock *lock)
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+{
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+ struct rt_mutex *m = &lock->rtmutex;
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+ struct task_struct *tsk;
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+
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+ /*
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+ * sem->readers can only hit 0 when a writer is waiting for the
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+ * active readers to leave the critical region.
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+ */
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+ if (!atomic_dec_and_test(&lock->readers))
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+ return;
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+
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+ raw_spin_lock_irq(&m->wait_lock);
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+ /*
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+ * Wake the writer, i.e. the rtmutex owner. It might release the
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+ * rtmutex concurrently in the fast path, but to clean up the rw
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+ * lock it needs to acquire m->wait_lock. The worst case which can
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+ * happen is a spurious wakeup.
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+ */
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+ tsk = rt_mutex_owner(m);
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+ if (tsk)
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+ wake_up_process(tsk);
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+
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+ raw_spin_unlock_irq(&m->wait_lock);
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+}
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+
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+static void __write_unlock_common(struct rt_rw_lock *lock, int bias,
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+ unsigned long flags)
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+{
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+ struct rt_mutex *m = &lock->rtmutex;
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+
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+ atomic_add(READER_BIAS - bias, &lock->readers);
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+ raw_spin_unlock_irqrestore(&m->wait_lock, flags);
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+ rt_spin_lock_slowunlock(m);
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+}
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+
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+void __sched __write_rt_lock(struct rt_rw_lock *lock)
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+{
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+ struct rt_mutex *m = &lock->rtmutex;
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+ struct task_struct *self = current;
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+ unsigned long flags;
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+
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+ /* Take the rtmutex as a first step */
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+ __rt_spin_lock(m);
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+
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+ /* Force readers into slow path */
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+ atomic_sub(READER_BIAS, &lock->readers);
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+
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+ raw_spin_lock_irqsave(&m->wait_lock, flags);
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+
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+ raw_spin_lock(&self->pi_lock);
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+ self->saved_state = self->state;
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+ __set_current_state_no_track(TASK_UNINTERRUPTIBLE);
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+ raw_spin_unlock(&self->pi_lock);
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+
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+ for (;;) {
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+ /* Have all readers left the critical region? */
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+ if (!atomic_read(&lock->readers)) {
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+ atomic_set(&lock->readers, WRITER_BIAS);
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+ raw_spin_lock(&self->pi_lock);
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+ __set_current_state_no_track(self->saved_state);
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+ self->saved_state = TASK_RUNNING;
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+ raw_spin_unlock(&self->pi_lock);
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+ raw_spin_unlock_irqrestore(&m->wait_lock, flags);
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+ return;
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+ }
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+
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+ raw_spin_unlock_irqrestore(&m->wait_lock, flags);
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+
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+ if (atomic_read(&lock->readers) != 0)
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+ schedule();
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+
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+ raw_spin_lock_irqsave(&m->wait_lock, flags);
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+
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+ raw_spin_lock(&self->pi_lock);
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+ __set_current_state_no_track(TASK_UNINTERRUPTIBLE);
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+ raw_spin_unlock(&self->pi_lock);
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+ }
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+}
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+
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+int __write_rt_trylock(struct rt_rw_lock *lock)
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+{
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+ struct rt_mutex *m = &lock->rtmutex;
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+ unsigned long flags;
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+
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+ if (!__rt_mutex_trylock(m))
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+ return 0;
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+
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+ atomic_sub(READER_BIAS, &lock->readers);
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+
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+ raw_spin_lock_irqsave(&m->wait_lock, flags);
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+ if (!atomic_read(&lock->readers)) {
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+ atomic_set(&lock->readers, WRITER_BIAS);
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+ raw_spin_unlock_irqrestore(&m->wait_lock, flags);
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+ return 1;
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+ }
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+ __write_unlock_common(lock, 0, flags);
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+ return 0;
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+}
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+
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+void __write_rt_unlock(struct rt_rw_lock *lock)
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+{
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+ struct rt_mutex *m = &lock->rtmutex;
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+ unsigned long flags;
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+
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+ raw_spin_lock_irqsave(&m->wait_lock, flags);
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+ __write_unlock_common(lock, WRITER_BIAS, flags);
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+}
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+
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+/* Map the reader biased implementation */
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+static inline int do_read_rt_trylock(rwlock_t *rwlock)
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+{
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+ return __read_rt_trylock(rwlock);
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+}
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+
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+static inline int do_write_rt_trylock(rwlock_t *rwlock)
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+{
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+ return __write_rt_trylock(rwlock);
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+}
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+
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+static inline void do_read_rt_lock(rwlock_t *rwlock)
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+{
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+ __read_rt_lock(rwlock);
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+}
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+
|
|
+static inline void do_write_rt_lock(rwlock_t *rwlock)
|
|
+{
|
|
+ __write_rt_lock(rwlock);
|
|
+}
|
|
+
|
|
+static inline void do_read_rt_unlock(rwlock_t *rwlock)
|
|
+{
|
|
+ __read_rt_unlock(rwlock);
|
|
+}
|
|
+
|
|
+static inline void do_write_rt_unlock(rwlock_t *rwlock)
|
|
+{
|
|
+ __write_rt_unlock(rwlock);
|
|
+}
|
|
+
|
|
+static inline void do_rwlock_rt_init(rwlock_t *rwlock, const char *name,
|
|
+ struct lock_class_key *key)
|
|
+{
|
|
+ __rwlock_biased_rt_init(rwlock, name, key);
|
|
+}
|
|
+
|
|
+int __lockfunc rt_read_can_lock(rwlock_t *rwlock)
|
|
+{
|
|
+ return atomic_read(&rwlock->readers) < 0;
|
|
+}
|
|
+
|
|
+int __lockfunc rt_write_can_lock(rwlock_t *rwlock)
|
|
+{
|
|
+ return atomic_read(&rwlock->readers) == READER_BIAS;
|
|
+}
|
|
+
|
|
+/*
|
|
+ * The common functions which get wrapped into the rwlock API.
|
|
+ */
|
|
+int __lockfunc rt_read_trylock(rwlock_t *rwlock)
|
|
+{
|
|
+ int ret;
|
|
+
|
|
+ migrate_disable();
|
|
+ ret = do_read_rt_trylock(rwlock);
|
|
+ if (ret)
|
|
+ rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_);
|
|
+ else
|
|
+ migrate_enable();
|
|
+ return ret;
|
|
+}
|
|
+EXPORT_SYMBOL(rt_read_trylock);
|
|
+
|
|
+int __lockfunc rt_write_trylock(rwlock_t *rwlock)
|
|
+{
|
|
+ int ret;
|
|
+
|
|
+ migrate_disable();
|
|
+ ret = do_write_rt_trylock(rwlock);
|
|
+ if (ret)
|
|
+ rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_);
|
|
+ else
|
|
+ migrate_enable();
|
|
+ return ret;
|
|
+}
|
|
+EXPORT_SYMBOL(rt_write_trylock);
|
|
+
|
|
+void __lockfunc rt_read_lock(rwlock_t *rwlock)
|
|
+{
|
|
+ migrate_disable();
|
|
+ rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_);
|
|
+ do_read_rt_lock(rwlock);
|
|
+}
|
|
+EXPORT_SYMBOL(rt_read_lock);
|
|
+
|
|
+void __lockfunc rt_write_lock(rwlock_t *rwlock)
|
|
+{
|
|
+ migrate_disable();
|
|
+ rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_);
|
|
+ do_write_rt_lock(rwlock);
|
|
+}
|
|
+EXPORT_SYMBOL(rt_write_lock);
|
|
+
|
|
+void __lockfunc rt_read_unlock(rwlock_t *rwlock)
|
|
+{
|
|
+ rwlock_release(&rwlock->dep_map, 1, _RET_IP_);
|
|
+ do_read_rt_unlock(rwlock);
|
|
+ migrate_enable();
|
|
+}
|
|
+EXPORT_SYMBOL(rt_read_unlock);
|
|
+
|
|
+void __lockfunc rt_write_unlock(rwlock_t *rwlock)
|
|
+{
|
|
+ rwlock_release(&rwlock->dep_map, 1, _RET_IP_);
|
|
+ do_write_rt_unlock(rwlock);
|
|
+ migrate_enable();
|
|
+}
|
|
+EXPORT_SYMBOL(rt_write_unlock);
|
|
+
|
|
+void __rt_rwlock_init(rwlock_t *rwlock, char *name, struct lock_class_key *key)
|
|
+{
|
|
+ do_rwlock_rt_init(rwlock, name, key);
|
|
+}
|
|
+EXPORT_SYMBOL(__rt_rwlock_init);
|