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Commit 5d0b7235 authored by Linus Torvalds's avatar Linus Torvalds Committed by H. Peter Anvin
Browse files

x86: clean up rwsem type system 



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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <alpine.LFD.2.00.1001121755220.17145@localhost.localdomain>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 3bef4447

arch/x86/include/asm/rwsem.h

+15 −10
Original line number Diff line number Diff line
@@ -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_semaphore *sem) 
 */

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(struct rw_semaphore *sem) 
 */

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"
@@ -170,7 +175,7 @@ static inline void __down_write(struct rw_semaphore *sem) 
 */

static inline int __down_write_trylock(struct rw_semaphore *sem)

{

	signed long ret = cmpxchg(&sem->count,

	rwsem_count_t ret = cmpxchg(&sem->count,

				    RWSEM_UNLOCKED_VALUE,

				    RWSEM_ACTIVE_WRITE_BIAS);

	if (ret == RWSEM_UNLOCKED_VALUE)
@@ -183,7 +188,7 @@ static inline int __down_write_trylock(struct rw_semaphore *sem) 
 */

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_semaphore *sem) 
 */

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 delta, struct rw_semaphore *sem) 
/*

 * 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)