417dcdf99e
_atomic_dec_and_lock() should not unconditionally take the lock before calling atomic_dec_and_test() in the UP case. For consistency reasons it should behave exactly like in the SMP case. Besides that this works around the problem that with CONFIG_DEBUG_SPINLOCK this spins in __spin_lock_debug() if the lock is already taken even if the counter doesn't drop to 0. Signed-off-by: Jan Blunck <jblunck@suse.de> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Nick Piggin <npiggin@suse.de> Cc: Valerie Aurora <vaurora@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
35 lines
782 B
C
35 lines
782 B
C
#include <linux/module.h>
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#include <linux/spinlock.h>
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#include <asm/atomic.h>
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/*
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* This is an implementation of the notion of "decrement a
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* reference count, and return locked if it decremented to zero".
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*
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* NOTE NOTE NOTE! This is _not_ equivalent to
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*
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* if (atomic_dec_and_test(&atomic)) {
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* spin_lock(&lock);
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* return 1;
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* }
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* return 0;
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*
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* because the spin-lock and the decrement must be
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* "atomic".
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*/
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int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
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{
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/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
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if (atomic_add_unless(atomic, -1, 1))
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return 0;
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/* Otherwise do it the slow way */
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spin_lock(lock);
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if (atomic_dec_and_test(atomic))
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return 1;
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spin_unlock(lock);
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return 0;
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}
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EXPORT_SYMBOL(_atomic_dec_and_lock);
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