From: Ingo Molnar <mingo@elte.hu>
Date: Tue, 7 Feb 2006 20:58:54 +0000 (-0800)
Subject: [PATCH] Fix spinlock debugging delays to not time out too early
X-Git-Tag: v2.6.16-rc3~112
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e0a602963485a2f109ae1521c0c55507304c63ed;p=linux-2.6

[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 <mingo@elte.hu>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/lib/spinlock_debug.c b/lib/spinlock_debug.c
index c8bb8cc899..d8b6bb419d 100644
--- a/lib/spinlock_debug.c
+++ b/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) {