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 <[email protected]>
rtvt123 · Apr 26, 2011 · 3dd2ee4 · 3dd2ee4
1 parent 5dd12af
commit 3dd2ee4
Showing 1 changed file with 4 additions and 4 deletions.
diff --git 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);