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/* * Assembly implementation of the mutex fastpath, based on atomic * decrement/increment. * * started by Ingo Molnar: * * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> */ #ifndef _ASM_MUTEX_H #define _ASM_MUTEX_H /** * __mutex_fastpath_lock - decrement and call function if negative * @v: pointer of type atomic_t * @fail_fn: function to call if the result is negative * * Atomically decrements @v and calls <fail_fn> if the result is negative. */ #define __mutex_fastpath_lock(v, fail_fn) \ do { \ unsigned long dummy; \ \ typecheck(atomic_t *, v); \ typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \ \ __asm__ __volatile__( \ LOCK " decl (%%rdi) \n" \ " js 2f \n" \ "1: \n" \ \ LOCK_SECTION_START("") \ "2: call "#fail_fn" \n" \ " jmp 1b \n" \ LOCK_SECTION_END \ \ :"=D" (dummy) \ : "D" (v) \ : "rax", "rsi", "rdx", "rcx", \ "r8", "r9", "r10", "r11", "memory"); \ } while (0) /** * __mutex_fastpath_lock_retval - try to take the lock by moving the count * from 1 to a 0 value * @count: pointer of type atomic_t * @fail_fn: function to call if the original value was not 1 * * Change the count from 1 to a value lower than 1, and call <fail_fn> if * it wasn't 1 originally. This function returns 0 if the fastpath succeeds, * or anything the slow path function returns */ static inline int __mutex_fastpath_lock_retval(atomic_t *count, int fastcall (*fail_fn)(atomic_t *)) { if (unlikely(atomic_dec_return(count) < 0)) return fail_fn(count); else return 0; } /** * __mutex_fastpath_unlock - increment and call function if nonpositive * @v: pointer of type atomic_t * @fail_fn: function to call if the result is nonpositive * * Atomically increments @v and calls <fail_fn> if the result is nonpositive. */ #define __mutex_fastpath_unlock(v, fail_fn) \ do { \ unsigned long dummy; \ \ typecheck(atomic_t *, v); \ typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \ \ __asm__ __volatile__( \ LOCK " incl (%%rdi) \n" \ " jle 2f \n" \ "1: \n" \ \ LOCK_SECTION_START("") \ "2: call "#fail_fn" \n" \ " jmp 1b \n" \ LOCK_SECTION_END \ \ :"=D" (dummy) \ : "D" (v) \ : "rax", "rsi", "rdx", "rcx", \ "r8", "r9", "r10", "r11", "memory"); \ } while (0) #define __mutex_slowpath_needs_to_unlock() 1 /** * __mutex_fastpath_trylock - try to acquire the mutex, without waiting * * @count: pointer of type atomic_t * @fail_fn: fallback function * * Change the count from 1 to 0 and return 1 (success), or return 0 (failure) * if it wasn't 1 originally. [the fallback function is never used on * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.] */ static inline int __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) { if (likely(atomic_cmpxchg(count, 1, 0) == 1)) return 1; else return 0; } #endif