Linus,
I found this bug in 2.4 kernel. I have verified that the bug exists on MIPS
SMP and PPC SMP, but not on i386 SMP. See the detailed explanation inside the
patch.
2.5 sched.c has been re-written quite a bit and does not have this problem.
http://linux.junsun.net/patches/generic/submitted/020515-2.4.18-smp-sched-typo.patch
Jun
Gcc will optimizie out the whole 'if' branch on platforms where
cycles_t is not unsigned long long (such as MIPS, PPC).
The symptom for this bug is not fatal - perhaps that is ther reason
why nobody has found it so far. Higher priority process will be delayed
to start its execution. One of my tests shows on a heavy-loaded system
the delay is about 5 to 6 jiffies.
Jun, 020515
diff -Nru link/kernel/sched.c.orig link/kernel/sched.c
--- link/kernel/sched.c.orig Fri Dec 21 09:42:04 2001
+++ link/kernel/sched.c Wed May 15 12:38:12 2002
@@ -282,7 +282,7 @@
target_tsk = tsk;
}
} else {
- if (oldest_idle == -1ULL) {
+ if (oldest_idle == (cycles_t)-1) {
int prio = preemption_goodness(tsk, p, cpu);
if (prio > max_prio) {
