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Commit 529b7307 authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt
Browse files

powerpc: Make rwsem use "long" type 



This makes the 64-bit kernel use 64-bit signed integers for the counter
(effectively supporting 32-bit of active count in the semaphore), thus
avoiding things like overflow of the mmap_sem if you use a really crazy
number of threads

Note: Ideally the type in the structure should be atomic_long_t rather
than "long". However, there's some nasty issues with that. It needs to
be initialized statically -and- lib/rwsem.c does things like

        sem->count = RWSEM_UNLOCKED_VALUE;

Now, if you mix in the fact that atomic_* types are actually structures
with one member and note typedefs of a scalar, it makes its really nasty.

So I stuck to what we did before using a long and casts for now.

Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent b1515af2

arch/powerpc/include/asm/rwsem.h

+37 −27
Original line number Diff line number Diff line
@@ -21,15 +21,20 @@ 
/*

 * the semaphore definition

 */

struct rw_semaphore {

	/* XXX this should be able to be an atomic_t  -- paulus */

	signed int		count;

#define RWSEM_UNLOCKED_VALUE		0x00000000

#define RWSEM_ACTIVE_BIAS		0x00000001

#define RWSEM_ACTIVE_MASK		0x0000ffff

#define RWSEM_WAITING_BIAS		(-0x00010000)

#ifdef CONFIG_PPC64

# define RWSEM_ACTIVE_MASK		0xffffffffL

#else

# define RWSEM_ACTIVE_MASK		0x0000ffffL

#endif



#define RWSEM_UNLOCKED_VALUE		0x00000000L

#define RWSEM_ACTIVE_BIAS		0x00000001L

#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)

#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS

#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)



struct rw_semaphore {

	long			count;

	spinlock_t		wait_lock;

	struct list_head	wait_list;

#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -44,8 +49,12 @@ struct rw_semaphore { 
#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) }

{								\

	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)
@@ -70,13 +79,13 @@ extern void __init_rwsem(struct rw_semaphore *sem, const char *name, 
 */

static inline void __down_read(struct rw_semaphore *sem)

{

	if (unlikely(atomic_inc_return((atomic_t *)(&sem->count)) <= 0))

	if (unlikely(atomic_long_inc_return((atomic_long_t *)&sem->count) <= 0))

		rwsem_down_read_failed(sem);

}



static inline int __down_read_trylock(struct rw_semaphore *sem)

{

	int tmp;

	long tmp;



	while ((tmp = sem->count) >= 0) {

		if (tmp == cmpxchg(&sem->count, tmp,
@@ -92,10 +101,10 @@ static inline int __down_read_trylock(struct rw_semaphore *sem) 
 */

static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)

{

	int tmp;

	long tmp;



	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,

				(atomic_t *)(&sem->count));

	tmp = atomic_long_add_return(RWSEM_ACTIVE_WRITE_BIAS,

				     (atomic_long_t *)&sem->count);

	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))

		rwsem_down_write_failed(sem);

}
@@ -107,7 +116,7 @@ static inline void __down_write(struct rw_semaphore *sem) 


static inline int __down_write_trylock(struct rw_semaphore *sem)

{

	int tmp;

	long tmp;



	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,

		      RWSEM_ACTIVE_WRITE_BIAS);
@@ -119,9 +128,9 @@ static inline int __down_write_trylock(struct rw_semaphore *sem) 
 */

static inline void __up_read(struct rw_semaphore *sem)

{

	int tmp;

	long tmp;



	tmp = atomic_dec_return((atomic_t *)(&sem->count));

	tmp = atomic_long_dec_return((atomic_long_t *)&sem->count);

	if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))

		rwsem_wake(sem);

}
@@ -131,17 +140,17 @@ static inline void __up_read(struct rw_semaphore *sem) 
 */

static inline void __up_write(struct rw_semaphore *sem)

{

	if (unlikely(atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,

			      (atomic_t *)(&sem->count)) < 0))

	if (unlikely(atomic_long_sub_return(RWSEM_ACTIVE_WRITE_BIAS,

				 (atomic_long_t *)&sem->count) < 0))

		rwsem_wake(sem);

}



/*

 * implement atomic add functionality

 */

static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)

static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)

{

	atomic_add(delta, (atomic_t *)(&sem->count));

	atomic_long_add(delta, (atomic_long_t *)&sem->count);

}



/*
@@ -149,9 +158,10 @@ static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem) 
 */

static inline void __downgrade_write(struct rw_semaphore *sem)

{

	int tmp;

	long tmp;



	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));

	tmp = atomic_long_add_return(-RWSEM_WAITING_BIAS,

				     (atomic_long_t *)&sem->count);

	if (tmp < 0)

		rwsem_downgrade_wake(sem);

}
@@ -159,14 +169,14 @@ static inline void __downgrade_write(struct rw_semaphore *sem) 
/*

 * implement exchange and add functionality

 */

static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)

static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)

{

	return atomic_add_return(delta, (atomic_t *)(&sem->count));

	return atomic_long_add_return(delta, (atomic_long_t *)&sem->count);

}



static inline int rwsem_is_locked(struct rw_semaphore *sem)

{

	return (sem->count != 0);

	return sem->count != 0;

}



#endif	/* __KERNEL__ */