[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 c8bb8cc..d8b6bb4 100644 (file)
--- 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) {