From 3dd2ee4824b668a635d6d2bb6bc73f33708cab9f Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 25 Apr 2011 18:10:58 -0700 Subject: [PATCH 1/1] 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 --- include/linux/bit_spinlock.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h index e612575a2596..b4326bfa684f 100644 --- a/include/linux/bit_spinlock.h +++ b/include/linux/bit_spinlock.h @@ -23,11 +23,11 @@ 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(); + preempt_enable(); + do { cpu_relax(); - preempt_disable(); - } + } while (test_bit(bitnum, addr)); + preempt_disable(); } #endif __acquire(bitlock); -- 2.39.2