From a57004e1afb6ee03c509f1b1ec74a000682ab93b Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Sun, 8 Jan 2006 01:02:19 -0800 Subject: [PATCH] atomic: dec_and_lock use atomic primitives Convert atomic_dec_and_lock to use new atomic primitives. Signed-off-by: Nick Piggin Cc: "Paul E. McKenney" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/dec_and_lock.c | 49 ++++++------------------------------------------- 1 file changed, 6 insertions(+), 43 deletions(-) diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c index 305a9663aee..a65c3145554 100644 --- a/lib/dec_and_lock.c +++ b/lib/dec_and_lock.c @@ -1,47 +1,11 @@ #include #include #include -#include -#ifdef __HAVE_ARCH_CMPXCHG /* * This is an implementation of the notion of "decrement a * reference count, and return locked if it decremented to zero". * - * This implementation can be used on any architecture that - * has a cmpxchg, and where atomic->value is an int holding - * the value of the atomic (i.e. the high bits aren't used - * for a lock or anything like that). - */ -int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) -{ - int counter; - int newcount; - - for (;;) { - counter = atomic_read(atomic); - newcount = counter - 1; - if (!newcount) - break; /* do it the slow way */ - - newcount = cmpxchg(&atomic->counter, counter, newcount); - if (newcount == counter) - return 0; - } - - spin_lock(lock); - if (atomic_dec_and_test(atomic)) - return 1; - spin_unlock(lock); - return 0; -} -#else -/* - * This is an architecture-neutral, but slow, - * implementation of the notion of "decrement - * a reference count, and return locked if it - * decremented to zero". - * * NOTE NOTE NOTE! This is _not_ equivalent to * * if (atomic_dec_and_test(&atomic)) { @@ -52,21 +16,20 @@ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) * * because the spin-lock and the decrement must be * "atomic". - * - * This slow version gets the spinlock unconditionally, - * and releases it if it isn't needed. Architectures - * are encouraged to come up with better approaches, - * this is trivially done efficiently using a load-locked - * store-conditional approach, for example. */ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) { +#ifdef CONFIG_SMP + /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */ + if (atomic_add_unless(atomic, -1, 1)) + return 0; +#endif + /* Otherwise do it the slow way */ spin_lock(lock); if (atomic_dec_and_test(atomic)) return 1; spin_unlock(lock); return 0; } -#endif EXPORT_SYMBOL(_atomic_dec_and_lock); -- cgit v1.2.3-18-g5258