Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 288 insertions, 0 deletions

diff --git a/include/asm-i386/rwsem.h b/include/asm-i386/rwsem.h
new file mode 100644
index 00000000000..7625a675852
--- /dev/null
+++ b/include/asm-i386/rwsem.h
@@ -0,0 +1,288 @@
+/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
+ *
+ * Written by David Howells (dhowells@redhat.com).
+ *
+ * Derived from asm-i386/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 _I386_RWSEM_H
+#define _I386_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>
+
+struct rwsem_waiter;
+
+extern struct rw_semaphore *FASTCALL(rwsem_down_read_failed(struct rw_semaphore *sem));
+extern struct rw_semaphore *FASTCALL(rwsem_down_write_failed(struct rw_semaphore *sem));
+extern struct rw_semaphore *FASTCALL(rwsem_wake(struct rw_semaphore *));
+extern struct rw_semaphore *FASTCALL(rwsem_downgrade_wake(struct rw_semaphore *sem));
+
+/*
+ * the semaphore definition
+ */
+struct rw_semaphore {
+        signed long             count;
+#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)
+        spinlock_t              wait_lock;
+        struct list_head        wait_list;
+#if RWSEM_DEBUG
+        int                     debug;
+#endif
+};
+
+/*
+ * initialisation
+ */
+#if RWSEM_DEBUG
+#define __RWSEM_DEBUG_INIT      , 0
+#else
+#define __RWSEM_DEBUG_INIT      /* */
+#endif
+
+#define __RWSEM_INITIALIZER(name) \
+{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, LIST_HEAD_INIT((name).wait_list) \
+        __RWSEM_DEBUG_INIT }
+
+#define DECLARE_RWSEM(name) \
+        struct rw_semaphore name = __RWSEM_INITIALIZER(name)
+
+static inline void init_rwsem(struct rw_semaphore *sem)
+{
+        sem->count = RWSEM_UNLOCKED_VALUE;
+        spin_lock_init(&sem->wait_lock);
+        INIT_LIST_HEAD(&sem->wait_list);
+#if RWSEM_DEBUG
+        sem->debug = 0;
+#endif
+}
+
+/*
+ * 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 */
+                "  js        2f\n\t" /* jump if we weren't granted the lock */
+                "1:\n\t"
+                LOCK_SECTION_START("")
+                "2:\n\t"
+                "  pushl     %%ecx\n\t"
+                "  pushl     %%edx\n\t"
+                "  call      rwsem_down_read_failed\n\t"
+                "  popl      %%edx\n\t"
+                "  popl      %%ecx\n\t"
+                "  jmp       1b\n"
+                LOCK_SECTION_END
+                "# ending down_read\n\t"
+                : "=m"(sem->count)
+                : "a"(sem), "m"(sem->count)
+                : "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(struct rw_semaphore *sem)
+{
+        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? */
+                "  jnz       2f\n\t" /* jump if we weren't granted the lock */
+                "1:\n\t"
+                LOCK_SECTION_START("")
+                "2:\n\t"
+                "  pushl     %%ecx\n\t"
+                "  call      rwsem_down_write_failed\n\t"
+                "  popl      %%ecx\n\t"
+                "  jmp       1b\n"
+                LOCK_SECTION_END
+                "# ending down_write"
+                : "=m"(sem->count), "=d"(tmp)
+                : "a"(sem), "1"(tmp), "m"(sem->count)
+                : "memory", "cc");
+}
+
+/*
+ * 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 */
+                "  js        2f\n\t" /* jump if the lock is being waited upon */
+                "1:\n\t"
+                LOCK_SECTION_START("")
+                "2:\n\t"
+                "  decw      %%dx\n\t" /* do nothing if still outstanding active readers */
+                "  jnz       1b\n\t"
+                "  pushl     %%ecx\n\t"
+                "  call      rwsem_wake\n\t"
+                "  popl      %%ecx\n\t"
+                "  jmp       1b\n"
+                LOCK_SECTION_END
+                "# ending __up_read\n"
+                : "=m"(sem->count), "=d"(tmp)
+                : "a"(sem), "1"(tmp), "m"(sem->count)
+                : "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 */
+                "  jnz       2f\n\t" /* jump if the lock is being waited upon */
+                "1:\n\t"
+                LOCK_SECTION_START("")
+                "2:\n\t"
+                "  decw      %%dx\n\t" /* did the active count reduce to 0? */
+                "  jnz       1b\n\t" /* jump back if not */
+                "  pushl     %%ecx\n\t"
+                "  call      rwsem_wake\n\t"
+                "  popl      %%ecx\n\t"
+                "  jmp       1b\n"
+                LOCK_SECTION_END
+                "# ending __up_write\n"
+                : "=m"(sem->count)
+                : "a"(sem), "i"(-RWSEM_ACTIVE_WRITE_BIAS), "m"(sem->count)
+                : "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 */
+                "  js        2f\n\t" /* jump if the lock is being waited upon */
+                "1:\n\t"
+                LOCK_SECTION_START("")
+                "2:\n\t"
+                "  pushl     %%ecx\n\t"
+                "  pushl     %%edx\n\t"
+                "  call      rwsem_downgrade_wake\n\t"
+                "  popl      %%edx\n\t"
+                "  popl      %%ecx\n\t"
+                "  jmp       1b\n"
+                LOCK_SECTION_END
+                "# ending __downgrade_write\n"
+                : "=m"(sem->count)
+                : "a"(sem), "i"(-RWSEM_WAITING_BIAS), "m"(sem->count)
+                : "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), "m"(sem->count));
+}
+
+/*
+ * 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,(%2)"
+                : "+r"(tmp), "=m"(sem->count)
+                : "r"(sem), "m"(sem->count)
+                : "memory");
+
+        return tmp+delta;
+}
+
+#endif /* __KERNEL__ */
+#endif /* _I386_RWSEM_H */