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authorAl Viro <viro@zeniv.linux.org.uk>2008-08-17 21:05:42 -0400
committerH. Peter Anvin <hpa@zytor.com>2008-10-22 22:55:20 -0700
commitbb8985586b7a906e116db835c64773b7a7d51663 (patch)
treede93ae58e88cc563d95cc124a73f3930594c6100 /arch/x86/include/asm/rwsem.h
parent8ede0bdb63305d3353efd97e9af6210afb05734e (diff)
x86, um: ... and asm-x86 move
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/include/asm/rwsem.h')
-rw-r--r--arch/x86/include/asm/rwsem.h265
1 files changed, 265 insertions, 0 deletions
diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
new file mode 100644
index 00000000000..3ff3015b71a
--- /dev/null
+++ b/arch/x86/include/asm/rwsem.h
@@ -0,0 +1,265 @@
+/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
+ *
+ * Written by David Howells (dhowells@redhat.com).
+ *
+ * Derived from asm-x86/semaphore.h
+ *
+ *
+ * The MSW of the count is the negated number of active writers and waiting
+ * lockers, and the LSW is the total number of active locks
+ *
+ * The lock count is initialized to 0 (no active and no waiting lockers).
+ *
+ * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
+ * uncontended lock. This can be determined because XADD returns the old value.
+ * Readers increment by 1 and see a positive value when uncontended, negative
+ * if there are writers (and maybe) readers waiting (in which case it goes to
+ * sleep).
+ *
+ * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
+ * be extended to 65534 by manually checking the whole MSW rather than relying
+ * on the S flag.
+ *
+ * The value of ACTIVE_BIAS supports up to 65535 active processes.
+ *
+ * This should be totally fair - if anything is waiting, a process that wants a
+ * lock will go to the back of the queue. When the currently active lock is
+ * released, if there's a writer at the front of the queue, then that and only
+ * that will be woken up; if there's a bunch of consequtive readers at the
+ * front, then they'll all be woken up, but no other readers will be.
+ */
+
+#ifndef ASM_X86__RWSEM_H
+#define ASM_X86__RWSEM_H
+
+#ifndef _LINUX_RWSEM_H
+#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
+#endif
+
+#ifdef __KERNEL__
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/lockdep.h>
+
+struct rwsem_waiter;
+
+extern asmregparm struct rw_semaphore *
+ rwsem_down_read_failed(struct rw_semaphore *sem);
+extern asmregparm struct rw_semaphore *
+ rwsem_down_write_failed(struct rw_semaphore *sem);
+extern asmregparm struct rw_semaphore *
+ rwsem_wake(struct rw_semaphore *);
+extern asmregparm struct rw_semaphore *
+ rwsem_downgrade_wake(struct rw_semaphore *sem);
+
+/*
+ * the semaphore definition
+ */
+
+#define RWSEM_UNLOCKED_VALUE 0x00000000
+#define RWSEM_ACTIVE_BIAS 0x00000001
+#define RWSEM_ACTIVE_MASK 0x0000ffff
+#define RWSEM_WAITING_BIAS (-0x00010000)
+#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
+#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
+
+struct rw_semaphore {
+ signed long count;
+ spinlock_t wait_lock;
+ struct list_head wait_list;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ struct lockdep_map dep_map;
+#endif
+};
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
+#else
+# define __RWSEM_DEP_MAP_INIT(lockname)
+#endif
+
+
+#define __RWSEM_INITIALIZER(name) \
+{ \
+ RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
+ LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) \
+}
+
+#define DECLARE_RWSEM(name) \
+ struct rw_semaphore name = __RWSEM_INITIALIZER(name)
+
+extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
+ struct lock_class_key *key);
+
+#define init_rwsem(sem) \
+do { \
+ static struct lock_class_key __key; \
+ \
+ __init_rwsem((sem), #sem, &__key); \
+} while (0)
+
+/*
+ * lock for reading
+ */
+static inline void __down_read(struct rw_semaphore *sem)
+{
+ asm volatile("# beginning down_read\n\t"
+ LOCK_PREFIX " incl (%%eax)\n\t"
+ /* adds 0x00000001, returns the old value */
+ " jns 1f\n"
+ " call call_rwsem_down_read_failed\n"
+ "1:\n\t"
+ "# ending down_read\n\t"
+ : "+m" (sem->count)
+ : "a" (sem)
+ : "memory", "cc");
+}
+
+/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+ __s32 result, tmp;
+ asm volatile("# beginning __down_read_trylock\n\t"
+ " movl %0,%1\n\t"
+ "1:\n\t"
+ " movl %1,%2\n\t"
+ " addl %3,%2\n\t"
+ " jle 2f\n\t"
+ LOCK_PREFIX " cmpxchgl %2,%0\n\t"
+ " jnz 1b\n\t"
+ "2:\n\t"
+ "# ending __down_read_trylock\n\t"
+ : "+m" (sem->count), "=&a" (result), "=&r" (tmp)
+ : "i" (RWSEM_ACTIVE_READ_BIAS)
+ : "memory", "cc");
+ return result >= 0 ? 1 : 0;
+}
+
+/*
+ * lock for writing
+ */
+static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+{
+ int tmp;
+
+ tmp = RWSEM_ACTIVE_WRITE_BIAS;
+ asm volatile("# beginning down_write\n\t"
+ LOCK_PREFIX " xadd %%edx,(%%eax)\n\t"
+ /* subtract 0x0000ffff, returns the old value */
+ " testl %%edx,%%edx\n\t"
+ /* was the count 0 before? */
+ " jz 1f\n"
+ " call call_rwsem_down_write_failed\n"
+ "1:\n"
+ "# ending down_write"
+ : "+m" (sem->count), "=d" (tmp)
+ : "a" (sem), "1" (tmp)
+ : "memory", "cc");
+}
+
+static inline void __down_write(struct rw_semaphore *sem)
+{
+ __down_write_nested(sem, 0);
+}
+
+/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+static inline int __down_write_trylock(struct rw_semaphore *sem)
+{
+ signed long ret = cmpxchg(&sem->count,
+ RWSEM_UNLOCKED_VALUE,
+ RWSEM_ACTIVE_WRITE_BIAS);
+ if (ret == RWSEM_UNLOCKED_VALUE)
+ return 1;
+ return 0;
+}
+
+/*
+ * unlock after reading
+ */
+static inline void __up_read(struct rw_semaphore *sem)
+{
+ __s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
+ asm volatile("# beginning __up_read\n\t"
+ LOCK_PREFIX " xadd %%edx,(%%eax)\n\t"
+ /* subtracts 1, returns the old value */
+ " jns 1f\n\t"
+ " call call_rwsem_wake\n"
+ "1:\n"
+ "# ending __up_read\n"
+ : "+m" (sem->count), "=d" (tmp)
+ : "a" (sem), "1" (tmp)
+ : "memory", "cc");
+}
+
+/*
+ * unlock after writing
+ */
+static inline void __up_write(struct rw_semaphore *sem)
+{
+ asm volatile("# beginning __up_write\n\t"
+ " movl %2,%%edx\n\t"
+ LOCK_PREFIX " xaddl %%edx,(%%eax)\n\t"
+ /* tries to transition
+ 0xffff0001 -> 0x00000000 */
+ " jz 1f\n"
+ " call call_rwsem_wake\n"
+ "1:\n\t"
+ "# ending __up_write\n"
+ : "+m" (sem->count)
+ : "a" (sem), "i" (-RWSEM_ACTIVE_WRITE_BIAS)
+ : "memory", "cc", "edx");
+}
+
+/*
+ * downgrade write lock to read lock
+ */
+static inline void __downgrade_write(struct rw_semaphore *sem)
+{
+ asm volatile("# beginning __downgrade_write\n\t"
+ LOCK_PREFIX " addl %2,(%%eax)\n\t"
+ /* transitions 0xZZZZ0001 -> 0xYYYY0001 */
+ " jns 1f\n\t"
+ " call call_rwsem_downgrade_wake\n"
+ "1:\n\t"
+ "# ending __downgrade_write\n"
+ : "+m" (sem->count)
+ : "a" (sem), "i" (-RWSEM_WAITING_BIAS)
+ : "memory", "cc");
+}
+
+/*
+ * implement atomic add functionality
+ */
+static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
+{
+ asm volatile(LOCK_PREFIX "addl %1,%0"
+ : "+m" (sem->count)
+ : "ir" (delta));
+}
+
+/*
+ * implement exchange and add functionality
+ */
+static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
+{
+ int tmp = delta;
+
+ asm volatile(LOCK_PREFIX "xadd %0,%1"
+ : "+r" (tmp), "+m" (sem->count)
+ : : "memory");
+
+ return tmp + delta;
+}
+
+static inline int rwsem_is_locked(struct rw_semaphore *sem)
+{
+ return (sem->count != 0);
+}
+
+#endif /* __KERNEL__ */
+#endif /* ASM_X86__RWSEM_H */