[PATCH] Fix spinlock debugging delays to not time out too early

The spinlock-debug wait-loop was using loops_per_jiffy to detect too long
spinlock waits - but on fast CPUs this led to a way too fast timeout and false
messages.

The fix is to include a __delay(1) call in the loop, to correctly approximate
the intended delay timeout of 1 second.  The code assumes that every
architecture implements __delay(1) to last around 1/(loops_per_jiffy*HZ)
seconds.

Signed-off-by: Ingo Molnar <[email protected]>
Cc: Andi Kleen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

lib/spinlock_debug.c

@@ -72,9 +72,9 @@ static void __spin_lock_debug(spinlock_t *lock)
 
 	for (;;) {
 		for (i = 0; i < loops_per_jiffy * HZ; i++) {
-			cpu_relax();
 			if (__raw_spin_trylock(&lock->raw_lock))
 				return;
+			__delay(1);
 		}
 		/* lockup suspected: */
 		if (print_once) {
@@ -144,9 +144,9 @@ static void __read_lock_debug(rwlock_t *lock)
 
 	for (;;) {
 		for (i = 0; i < loops_per_jiffy * HZ; i++) {
-			cpu_relax();
 			if (__raw_read_trylock(&lock->raw_lock))
 				return;
+			__delay(1);
 		}
 		/* lockup suspected: */
 		if (print_once) {
@@ -217,9 +217,9 @@ static void __write_lock_debug(rwlock_t *lock)
 
 	for (;;) {
 		for (i = 0; i < loops_per_jiffy * HZ; i++) {
-			cpu_relax();
 			if (__raw_write_trylock(&lock->raw_lock))
 				return;
+			__delay(1);
 		}
 		/* lockup suspected: */
 		if (print_once) {