Commit 3dd2ee48 authored Apr 25, 2011 by Linus Torvalds

bit_spinlock: don't play preemption games inside the busy loop



When we are waiting for the bit-lock to be released, and are looping
over the 'cpu_relax()' should not be doing anything else - otherwise we
miss the point of trying to do the whole 'cpu_relax()'.

Do the preemption enable/disable around the loop, rather than inside of
it.

Noticed when I was looking at the code generation for the dcache
__d_drop usage, and the code just looked very odd.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 5dd12af0

include/linux/bit_spinlock.h

+4 −4

Original line number	Diff line number	Diff line
		@@ -23,12 +23,12 @@ static inline void bit_spin_lock(int bitnum, unsigned long *addr)
		preempt_disable();
		#if defined(CONFIG_SMP) \|\| defined(CONFIG_DEBUG_SPINLOCK)
		while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
		while (test_bit(bitnum, addr)) {
		preempt_enable();
		do {
		cpu_relax();
		} while (test_bit(bitnum, addr));
		preempt_disable();
		}
		}
		#endif
		__acquire(bitlock);
		}