Hi Juri,
On Tue, Mar 24, 2015 at 09:27:09AM +0000, Juri Lelli wrote:
>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.
I remember you mentioned that there is a bug through IRC last week, if this
patch solve it?
Regards,
Wanpeng Li
>
>Thanks,
>
>- Juri
>
>>From 65e8033e05f8b70116747062d00d5a5c266699fb Mon Sep 17 00:00:00 2001
>From: Juri Lelli <juri.le...@gmail.com>
>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 <juri.le...@arm.com>
>---
> 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
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