[Xen-devel] [RFC PATCH 02/33] Add sync bitops

[Chris Wright <chrisw@xxxxxxxxxxxx>]

Add "always lock'd" implementations of set_bit, clear_bit and
change_bit and the corresponding test_and_ functions.  Also add
"always lock'd" implementation of cmpxchg.  These give guaranteed
strong synchronisation and are required for non-SMP kernels running on
an SMP hypervisor.

Signed-off-by: Ian Pratt <ian.pratt@xxxxxxxxxxxxx>
Signed-off-by: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
Cc: Christoph Lameter <clameter@xxxxxxx>
---
 include/asm-i386/synch_bitops.h |  166 ++++++++++++++++++++++++++++++++++++++++
 include/asm-i386/system.h       |   33 +++++++
 2 files changed, 199 insertions(+)

diff -r 935903fb1136 include/asm-i386/system.h
--- a/include/asm-i386/system.h Mon May 08 19:20:42 2006 -0400
+++ b/include/asm-i386/system.h Mon May 08 19:27:04 2006 -0400
@@ -263,6 +263,9 @@ static inline unsigned long __xchg(unsig
 #define cmpxchg(ptr,o,n)\
        ((__typeof__(*(ptr)))__cmpxchg((ptr),(unsigned long)(o),\
                                        (unsigned long)(n),sizeof(*(ptr))))
+#define synch_cmpxchg(ptr,o,n)\
+       ((__typeof__(*(ptr)))__synch_cmpxchg((ptr),(unsigned long)(o),\
+                                       (unsigned long)(n),sizeof(*(ptr))))
 #endif
 
 static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
@@ -291,6 +294,36 @@ static inline unsigned long __cmpxchg(vo
        }
        return old;
 }
+
+#define __LOCK_PREFIX "lock ; "
+static inline unsigned long __synch_cmpxchg(volatile void *ptr,
+                                           unsigned long old,
+                                           unsigned long new, int size)
+{
+       unsigned long prev;
+       switch (size) {
+       case 1:
+               __asm__ __volatile__(__LOCK_PREFIX "cmpxchgb %b1,%2"
+                                    : "=a"(prev)
+                                    : "q"(new), "m"(*__xg(ptr)), "0"(old)
+                                    : "memory");
+               return prev;
+       case 2:
+               __asm__ __volatile__(__LOCK_PREFIX "cmpxchgw %w1,%2"
+                                    : "=a"(prev)
+                                    : "r"(new), "m"(*__xg(ptr)), "0"(old)
+                                    : "memory");
+               return prev;
+       case 4:
+               __asm__ __volatile__(__LOCK_PREFIX "cmpxchgl %1,%2"
+                                    : "=a"(prev)
+                                    : "r"(new), "m"(*__xg(ptr)), "0"(old)
+                                    : "memory");
+               return prev;
+       }
+       return old;
+}
+#undef __LOCK_PREFIX
 
 #ifndef CONFIG_X86_CMPXCHG
 /*
diff -r 935903fb1136 include/asm-i386/synch_bitops.h
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-i386/synch_bitops.h   Mon May 08 19:27:04 2006 -0400
@@ -0,0 +1,166 @@
+#ifndef _I386_SYNCH_BITOPS_H
+#define _I386_SYNCH_BITOPS_H
+
+/*
+ * Copyright 1992, Linus Torvalds.
+ */
+
+/* make sure these are always locked */
+#define __LOCK_PREFIX "lock ; "
+
+/*
+ * These have to be done with inline assembly: that way the bit-setting
+ * is guaranteed to be atomic. All bit operations return 0 if the bit
+ * was cleared before the operation and != 0 if it was not.
+ *
+ * bit 0 is the LSB of addr; bit 32 is the LSB of (addr+1).
+ */
+
+#define ADDR (*(volatile long *) addr)
+
+/**
+ * synch_set_bit - Atomically set a bit in memory
+ * @nr: the bit to set
+ * @addr: the address to start counting from
+ *
+ * This function is atomic and may not be reordered.  See __set_bit()
+ * if you do not require the atomic guarantees.
+ *
+ * Note: there are no guarantees that this function will not be reordered
+ * on non x86 architectures, so if you are writting portable code,
+ * make sure not to rely on its reordering guarantees.
+ *
+ * Note that @nr may be almost arbitrarily large; this function is not
+ * restricted to acting on a single-word quantity.
+ */
+static inline void synch_set_bit(int nr, volatile unsigned long * addr)
+{
+       __asm__ __volatile__( __LOCK_PREFIX
+               "btsl %1,%0"
+               :"+m" (ADDR)
+               :"Ir" (nr)
+               : "memory");
+}
+
+/**
+ * synch_clear_bit - Clears a bit in memory
+ * @nr: Bit to clear
+ * @addr: Address to start counting from
+ *
+ * synch_clear_bit() is atomic and may not be reordered.  However, it does
+ * not contain a memory barrier, so if it is used for locking purposes,
+ * you should call smp_mb__before_clear_bit() and/or smp_mb__after_clear_bit()
+ * in order to ensure changes are visible on other processors.
+ */
+static inline void synch_clear_bit(int nr, volatile unsigned long * addr)
+{
+       __asm__ __volatile__( __LOCK_PREFIX
+               "btrl %1,%0"
+               :"+m" (ADDR)
+               :"Ir" (nr)
+               : "memory");
+}
+
+/**
+ * synch_change_bit - Toggle a bit in memory
+ * @nr: Bit to change
+ * @addr: Address to start counting from
+ *
+ * change_bit() is atomic and may not be reordered. It may be
+ * reordered on other architectures than x86.
+ * Note that @nr may be almost arbitrarily large; this function is not
+ * restricted to acting on a single-word quantity.
+ */
+static inline void synch_change_bit(int nr, volatile unsigned long * addr)
+{
+       __asm__ __volatile__( __LOCK_PREFIX
+               "btcl %1,%0"
+               :"+m" (ADDR)
+               :"Ir" (nr)
+               : "memory");
+}
+
+/**
+ * synch_test_and_set_bit - Set a bit and return its old value
+ * @nr: Bit to set
+ * @addr: Address to count from
+ *
+ * This operation is atomic and cannot be reordered.  
+ * It may be reordered on other architectures than x86.
+ * It also implies a memory barrier.
+ */
+static inline int synch_test_and_set_bit(int nr, volatile unsigned long * addr)
+{
+       int oldbit;
+
+       __asm__ __volatile__( __LOCK_PREFIX
+               "btsl %2,%1\n\tsbbl %0,%0"
+               :"=r" (oldbit),"+m" (ADDR)
+               :"Ir" (nr) : "memory");
+       return oldbit;
+}
+
+/**
+ * synch_test_and_clear_bit - Clear a bit and return its old value
+ * @nr: Bit to clear
+ * @addr: Address to count from
+ *
+ * This operation is atomic and cannot be reordered.
+ * It can be reorderdered on other architectures other than x86.
+ * It also implies a memory barrier.
+ */
+static inline int synch_test_and_clear_bit(int nr, volatile unsigned long * 
addr)
+{
+       int oldbit;
+
+       __asm__ __volatile__( __LOCK_PREFIX
+               "btrl %2,%1\n\tsbbl %0,%0"
+               :"=r" (oldbit),"+m" (ADDR)
+               :"Ir" (nr) : "memory");
+       return oldbit;
+}
+
+/**
+ * synch_test_and_change_bit - Change a bit and return its old value
+ * @nr: Bit to change
+ * @addr: Address to count from
+ *
+ * This operation is atomic and cannot be reordered.  
+ * It also implies a memory barrier.
+ */
+static inline int synch_test_and_change_bit(int nr, volatile unsigned long* 
addr)
+{
+       int oldbit;
+
+       __asm__ __volatile__( __LOCK_PREFIX
+               "btcl %2,%1\n\tsbbl %0,%0"
+               :"=r" (oldbit),"+m" (ADDR)
+               :"Ir" (nr) : "memory");
+       return oldbit;
+}
+
+static __always_inline int synch_const_test_bit(int nr, const volatile 
unsigned long *addr)
+{
+       return ((1UL << (nr & 31)) &
+               (((const volatile unsigned int *)addr)[nr >> 5])) != 0;
+}
+
+static inline int synch_var_test_bit(int nr, const volatile unsigned long * 
addr)
+{
+       int oldbit;
+
+       __asm__ __volatile__(
+               "btl %2,%1\n\tsbbl %0,%0"
+               :"=r" (oldbit)
+               :"m" (ADDR),"Ir" (nr));
+       return oldbit;
+}
+
+#define synch_test_bit(nr,addr) \
+(__builtin_constant_p(nr) ? \
+ synch_constant_test_bit((nr),(addr)) : \
+ synch_var_test_bit((nr),(addr)))
+
+#undef ADDR
+
+#endif /* _I386_SYNCH_BITOPS_H */

--

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