Hi,
On 23/03/2015 08:55, Peter Zijlstra wrote:
> On Mon, Mar 23, 2015 at 08:25:04AM +0100, Ingo Molnar wrote:
>>>>>>>>> + if (cpu >= nr_cpu_ids) {
>>>>>>>>> + if (dl_bandwidth_enabled()) {
>>>>>>>>> + /*
>>>>>>>>> + * Fail to find any suitable
>>>>>>>>> cpu.
>>>>>>>>> + * The task will never come
>>>>>>>>> back!
>>>>>>>>> + */
>>>>>>>>> + WARN_ON(1);
>>>>>>>>
>>>>>>>> Can this condition happen to users with a non-buggy kernel?
>
>> I still haven't seen a satisfactory answer to this question. Please
>> don't resend patches without clearing questions raised during review.
>
> So I had a look on Friday, it _should_ not happen, but it does due to a
> second bug Juri is currently chasing down.
>
Right, it should not happen. It happens because hotplug operations are
destructive w.r.t. cpusets. Peter, how about we move the check you put
in sched_cpu_inactive() to cpuset_cpu_inactive()? This way, if we fail,
we don't need to destroy/rebuild the domains.
Thanks,
- Juri
>From 65e8033e05f8b70116747062d00d5a5c266699fb Mon Sep 17 00:00:00 2001
From: Juri Lelli <[email protected]>
Date: Tue, 24 Mar 2015 07:47:03 +0000
Subject: [PATCH] sched/core: check for available -dl bandwidth in
cpuset_cpu_inactive
Signed-off-by: Juri Lelli <[email protected]>
---
kernel/sched/core.c | 56 ++++++++++++++++++++++++++---------------------------
1 file changed, 28 insertions(+), 28 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 50927eb..3723ad0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5318,36 +5318,13 @@ static int sched_cpu_active(struct notifier_block *nfb,
static int sched_cpu_inactive(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
- unsigned long flags;
- long cpu = (long)hcpu;
- struct dl_bw *dl_b;
-
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_DOWN_PREPARE:
- set_cpu_active(cpu, false);
-
- /* explicitly allow suspend */
- if (!(action & CPU_TASKS_FROZEN)) {
- bool overflow;
- int cpus;
-
- rcu_read_lock_sched();
- dl_b = dl_bw_of(cpu);
-
- raw_spin_lock_irqsave(&dl_b->lock, flags);
- cpus = dl_bw_cpus(cpu);
- overflow = __dl_overflow(dl_b, cpus, 0, 0);
- raw_spin_unlock_irqrestore(&dl_b->lock, flags);
-
- rcu_read_unlock_sched();
-
- if (overflow)
- return notifier_from_errno(-EBUSY);
- }
+ set_cpu_active((long)hcpu, false);
return NOTIFY_OK;
+ default:
+ return NOTIFY_DONE;
}
-
- return NOTIFY_DONE;
}
static int __init migration_init(void)
@@ -7001,7 +6978,6 @@ static int cpuset_cpu_active(struct notifier_block *nfb,
unsigned long action,
*/
case CPU_ONLINE:
- case CPU_DOWN_FAILED:
cpuset_update_active_cpus(true);
break;
default:
@@ -7013,8 +6989,32 @@ static int cpuset_cpu_active(struct notifier_block *nfb,
unsigned long action,
static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long
action,
void *hcpu)
{
- switch (action) {
+ unsigned long flags;
+ long cpu = (long)hcpu;
+ struct dl_bw *dl_b;
+
+ switch (action & ~CPU_TASKS_FROZEN) {
case CPU_DOWN_PREPARE:
+ /* explicitly allow suspend */
+ if (!(action & CPU_TASKS_FROZEN)) {
+ bool overflow;
+ int cpus;
+
+ rcu_read_lock_sched();
+ dl_b = dl_bw_of(cpu);
+
+ raw_spin_lock_irqsave(&dl_b->lock, flags);
+ cpus = dl_bw_cpus(cpu);
+ overflow = __dl_overflow(dl_b, cpus, 0, 0);
+ raw_spin_unlock_irqrestore(&dl_b->lock, flags);
+
+ rcu_read_unlock_sched();
+
+ if (overflow) {
+ trace_printk("hotplug failed for cpu %lu", cpu);
+ return notifier_from_errno(-EBUSY);
+ }
+ }
cpuset_update_active_cpus(false);
break;
case CPU_DOWN_PREPARE_FROZEN:
--
2.3.0
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
