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Date: Tue, 12 Jan 2010 17:57:35 -0800 (PST) From: Linus Torvalds <torvalds@...ux-foundation.org> To: "H. Peter Anvin" <hpa@...or.com> cc: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: 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: Linus Torvalds <torvalds@...ux-foundation.org> --- Ok, this is the final cleanup. With this, the <asm/rwsem.h> header file should be usable on x86-64 too. It needs some more support functions (the actual rwsem asm->C trampoline functions that save/restore all the clobbered registers etc), but that's a separate thing. Similarly, this will need further changes for actual 64-bit counters. The 32767-thread limit is fine on x86-32 (we're thread-limited by lowmem anyway), but likely not on x86-64. Comments? diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h index e9480be..705265f 100644 --- 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_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" "1:\n\t" " mov %1,%2\n\t" @@ -142,7 +147,7 @@ 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" @@ -169,9 +174,9 @@ 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_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; @@ -182,7 +187,7 @@ 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 */ @@ -200,7 +205,7 @@ 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 @@ -244,9 +249,9 @@ 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) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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