Hi Andrew,
I found an off by one error in your recent cond_resched fix. In
cond_resched_lock() it calls __resched_legal()
before dropping the spin lock. __resched_legal() will
always finds the preempt_count non-zero and will prevent
the call to __cond_resched().
The attached patch adds a parameter to __resched_legal()
with the expected preempt_count value. The patch was made
against a Linus's git tree. It will apply cleanly to
linux-2.6.18-rc2.
Jim Houston - Concurrent Computer Corp.
--
--- linux-2.6/kernel/sched.c.orig 2006-07-17 09:30:05.000000000 -0400
+++ linux-2.6/kernel/sched.c 2006-07-17 23:00:50.000000000 -0400
@@ -4456,9 +4456,9 @@
return 0;
}
-static inline int __resched_legal(void)
+static inline int __resched_legal(int expected_preempt_count)
{
- if (unlikely(preempt_count()))
+ if (unlikely(preempt_count() != expected_preempt_count))
return 0;
if (unlikely(system_state != SYSTEM_RUNNING))
return 0;
@@ -4484,7 +4484,7 @@
int __sched cond_resched(void)
{
- if (need_resched() && __resched_legal()) {
+ if (need_resched() && __resched_legal(0)) {
__cond_resched();
return 1;
}
@@ -4510,7 +4510,7 @@
ret = 1;
spin_lock(lock);
}
- if (need_resched() && __resched_legal()) {
+ if (need_resched() && __resched_legal(1)) {
spin_release(&lock->dep_map, 1, _THIS_IP_);
_raw_spin_unlock(lock);
preempt_enable_no_resched();
@@ -4526,7 +4526,7 @@
{
BUG_ON(!in_softirq());
- if (need_resched() && __resched_legal()) {
+ if (need_resched() && __resched_legal(0)) {
raw_local_irq_disable();
_local_bh_enable();
raw_local_irq_enable();
-
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