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Subject[PATCH] sched: Make cond_resched*() available earlier
Using early netconsole and gianfar driver this error pops up:

netconsole: timeout waiting for carrier

It appears that net/core/netpoll.c:netpoll_setup() is using
cond_resched() in a loop waiting for a carrier.

The thing is that cond_resched() is a no-op when system_state !=
SYSTEM_RUNNING, and so drivers/net/phy/phy.c's state_queue is never
scheduled, therefore link detection doesn't work.

The system_state check exists to avoid very early calls to the
scheduler. Though, using cond_resched() should be safe after scheduler
is initialized, so instead of checking the system_state, we can test
that the scheduler is running, therefore making cond_resched() and
friends available much earlier (but not too much).

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
On Wed, Jul 08, 2009 at 02:58:46PM +0200, Peter Zijlstra wrote:
[...]
> > > > Hm. Speaking of cond_resched*() only, then it should be pretty
> > > > safe to convert the SYSTEM_RUNNING checks to scheduler_running,
> > > > no? scheduler_running is set after sched_init().
> > >
> > > Hmm, that might work, I'd have to audit sched_init_smp() as it seems to
> > > do way too much...
> >
> > sched_init_smp() is called from the kernel_thread(), so
> > if the scheduler is not functional prior to kernel_thread(),
> > you're in trouble anyway, no? The point is that a lot of
> > code is calling schedule() prior to sched_init_smp()
> > (e.g. msleep(), mutexes), and there are no issues. So
> > should be no issues with cond_resched()?
>
> Yeah, it should be good, I just got paranoid looking at
> sched_init_smp().

OK, thanks everyone for the reviews.

Here is an updated patch. As usual, tested on UP PowerPC, with and
without SMP, PREEMPT and PREEMPT_VOLUNTARY.

kernel/sched.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 7c9098d..555360b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6561,7 +6561,7 @@ static void __cond_resched(void)
int __sched _cond_resched(void)
{
if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE) &&
- system_state == SYSTEM_RUNNING) {
+ scheduler_running) {
__cond_resched();
return 1;
}
@@ -6579,7 +6579,7 @@ EXPORT_SYMBOL(_cond_resched);
*/
int cond_resched_lock(spinlock_t *lock)
{
- int resched = need_resched() && system_state == SYSTEM_RUNNING;
+ int resched = need_resched() && scheduler_running;
int ret = 0;

if (spin_needbreak(lock) || resched) {
@@ -6599,7 +6599,7 @@ int __sched cond_resched_softirq(void)
{
BUG_ON(!in_softirq());

- if (need_resched() && system_state == SYSTEM_RUNNING) {
+ if (need_resched() && scheduler_running) {
local_bh_enable();
__cond_resched();
local_bh_disable();
--
1.6.3.3


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