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From: Greg KH on 22 Apr 2010 15:50
2.6.32-stable review patch. If anyone has any objections, please let us know.

------------------

From: Linus Torvalds <torvalds(a)linux-foundation.org>

commit 5d0b7235d83eefdafda300656e97d368afcafc9a upstream.

The fast version of the rwsems (the code that uses xadd) has
traditionally only worked on x86-32, and as a result it mixes different
kinds of types wildly - they just all happen to be 32-bit. We have
"long", we have "__s32", and we have "int".

To make it work on x86-64, the types suddenly matter a lot more. It can
be either a 32-bit or 64-bit signed type, and both work (with the caveat
that a 32-bit counter will only have 15 bits of effective write
counters, so it's limited to 32767 users). But whatever type you
choose, it needs to be used consistently.

This makes a new 'rwsem_counter_t', that is a 32-bit signed type. For a
64-bit type, you'd need to also update the BIAS values.

Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
LKML-Reference: <alpine.LFD.2.00.1001121755220.17145(a)localhost.localdomain>
Signed-off-by: H. Peter Anvin <hpa(a)zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
arch/x86/include/asm/rwsem.h | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)

--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -55,6 +55,9 @@ extern asmregparm struct rw_semaphore *

/*
* the semaphore definition
+ *
+ * The bias values and the counter type needs to be extended to 64 bits
+ * if we want to have more than 32767 potential readers/writers
*/

#define RWSEM_UNLOCKED_VALUE 0x00000000
@@ -64,8 +67,10 @@ extern asmregparm struct rw_semaphore *
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)

+typedef signed int rwsem_count_t;
+
struct rw_semaphore {
- signed long count;
+ rwsem_count_t count;
spinlock_t wait_lock;
struct list_head wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -121,7 +126,7 @@ static inline void __down_read(struct rw
*/
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
- __s32 result, tmp;
+ rwsem_count_t result, tmp;
asm volatile("# beginning __down_read_trylock\n\t"
" mov %0,%1\n\t"
"1:\n\t"
@@ -143,7 +148,7 @@ static inline int __down_read_trylock(st
*/
static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
- int tmp;
+ rwsem_count_t tmp;

tmp = RWSEM_ACTIVE_WRITE_BIAS;
asm volatile("# beginning down_write\n\t"
@@ -170,9 +175,9 @@ static inline void __down_write(struct r
*/
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
- signed long ret = cmpxchg(&sem->count,
- RWSEM_UNLOCKED_VALUE,
- RWSEM_ACTIVE_WRITE_BIAS);
+ rwsem_count_t ret = cmpxchg(&sem->count,
+ RWSEM_UNLOCKED_VALUE,
+ RWSEM_ACTIVE_WRITE_BIAS);
if (ret == RWSEM_UNLOCKED_VALUE)
return 1;
return 0;
@@ -183,7 +188,7 @@ static inline int __down_write_trylock(s
*/
static inline void __up_read(struct rw_semaphore *sem)
{
- __s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
+ rwsem_count_t tmp = -RWSEM_ACTIVE_READ_BIAS;
asm volatile("# beginning __up_read\n\t"
LOCK_PREFIX " xadd %1,(%2)\n\t"
/* subtracts 1, returns the old value */
@@ -201,7 +206,7 @@ static inline void __up_read(struct rw_s
*/
static inline void __up_write(struct rw_semaphore *sem)
{
- unsigned long tmp;
+ rwsem_count_t tmp;
asm volatile("# beginning __up_write\n\t"
LOCK_PREFIX " xadd %1,(%2)\n\t"
/* tries to transition
@@ -245,9 +250,9 @@ static inline void rwsem_atomic_add(int
/*
* implement exchange and add functionality
*/
-static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
+static inline rwsem_count_t rwsem_atomic_update(int delta, struct rw_semaphore *sem)
{
- int tmp = delta;
+ rwsem_count_t tmp = delta;

asm volatile(LOCK_PREFIX "xadd %0,%1"
: "+r" (tmp), "+m" (sem->count)


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