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>
diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
index e612575..b4326bf 100644
--- a/include/linux/bit_spinlock.h
+++ b/include/linux/bit_spinlock.h
@@ -23,11 +23,11 @@
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);