Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Michael Wang]

On 05/20/2013 02:58 PM, Michael Wang wrote:
> On 05/20/2013 02:47 PM, Borislav Petkov wrote:
>> On Mon, May 20, 2013 at 02:23:37PM +0800, Michael Wang wrote:
>>> On 05/20/2013 12:50 PM, Borislav Petkov wrote:
>>>> On Mon, May 20, 2013 at 11:16:33AM +0800, Michael Wang wrote:
>>>>> I suppose the reason is that the cpu we passed to
>>>>> mod_delayed_work_on() has a chance to become offline before we
>>>>> disabled irq, what about check it before send resched ipi? like:
>>>>
>>>> I think this is only addressing the symptoms - what we should be doing
>>>> instead is asking ourselves why are we even scheduling work on a cpu if
>>>> the machine goes offline?
>>>>
>>>> I don't know though who should be responsible for killing all that
>>>> work - the workqueue itself or the guy who created it, i.e. cpufreq
>>>> governor...
>>>
>>> So there are two questions here:
>>> 1. Is gov_queue_work() want to queue the work on offline cpu?
>>> 2. Is mod_delayed_work_on() allow offline cpu?
>>>
>>> I guess both should be false?
>>
>> Well, if we don't allow queueing work on a cpu which goes offline, i.e.
>> #2, the problem should be solved.
> 
> I've take a look at the usage of queue_delayed_work_on() and
> mod_delayed_work_on(), mostly passed this_cpu, or those in online mask,
> I think offline cpu is not by designed.
> 
> Besides, the cpu gov_queue_work() is using 'policy->cpus' which seems to
> be updated during UP DOWN notify, I think they are supposed to be online.
> 
> But we need expert in cpufreq to confirm all these...

And I guess this may help to reduce the chance to trigger WARN:

diff --git a/drivers/cpufreq/cpufreq_governor.c
b/drivers/cpufreq/cpufreq_governor.c
index 443442d..0f96013 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -180,7 +180,7 @@ void gov_queue_work(struct dbs_data *dbs_data,
struct cpufreq_policy *policy,
        if (!all_cpus) {
                __gov_queue_work(smp_processor_id(), dbs_data, delay);
        } else {
-               for_each_cpu(i, policy->cpus)
+               for_each_cpu_and(i, policy->cpus, cpu_online_mask)
                        __gov_queue_work(i, dbs_data, delay);
        }
 }

Well, disable irq will be better, anyway...still need folks who own that
driver to make the decision, so let's CC them :)

Regards,
Michael Wang


> 
> Regards,
> Michael Wang
> 
>>
>> Tejun?
>>
>> Here are the splats: http://marc.info/?l=linux-kernel&m=136879901425951
>>
> 
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> 

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Viresh Kumar]

Hi Michael,

I haven't followed this mail chain earlier and saw this mail only as I am
added in cc now. I probably have answers to few questions here:

On 20 May 2013 12:36, Michael Wang <wangyun@linux.vnet.ibm.com> wrote:
> On 05/20/2013 02:58 PM, Michael Wang wrote:
>> On 05/20/2013 02:47 PM, Borislav Petkov wrote:
>>> On Mon, May 20, 2013 at 02:23:37PM +0800, Michael Wang wrote:
>>>> On 05/20/2013 12:50 PM, Borislav Petkov wrote:
>>>> So there are two questions here:
>>>> 1. Is gov_queue_work() want to queue the work on offline cpu?

No. We are only working with online cpus now in cpufreq core and governors.

>> Besides, the cpu gov_queue_work() is using 'policy->cpus' which seems to
>> be updated during UP DOWN notify, I think they are supposed to be online.
>>
>> But we need expert in cpufreq to confirm all these...

I confirm this. policy->cpus only contains online cpus.. and
policy->related_cpus
always contain online+offline cpus.

> And I guess this may help to reduce the chance to trigger WARN:
>
> diff --git a/drivers/cpufreq/cpufreq_governor.c
> b/drivers/cpufreq/cpufreq_governor.c
> index 443442d..0f96013 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -180,7 +180,7 @@ void gov_queue_work(struct dbs_data *dbs_data,
> struct cpufreq_policy *policy,
>         if (!all_cpus) {
>                 __gov_queue_work(smp_processor_id(), dbs_data, delay);
>         } else {
> -               for_each_cpu(i, policy->cpus)
> +               for_each_cpu_and(i, policy->cpus, cpu_online_mask)
>                         __gov_queue_work(i, dbs_data, delay);
>         }
>  }

Not required at all... policy->cpus is guaranteed to have only online cpus.

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Michael Wang]

Hi, Viresh
On 05/20/2013 03:12 PM, Viresh Kumar wrote:
> Hi Michael,
> 
> I haven't followed this mail chain earlier and saw this mail only as I am
> added in cc now. I probably have answers to few questions here:

Thanks for your quick respond :)

> 
> On 20 May 2013 12:36, Michael Wang <wangyun@linux.vnet.ibm.com> wrote:
>> On 05/20/2013 02:58 PM, Michael Wang wrote:
>>> On 05/20/2013 02:47 PM, Borislav Petkov wrote:
>>>> On Mon, May 20, 2013 at 02:23:37PM +0800, Michael Wang wrote:
>>>>> On 05/20/2013 12:50 PM, Borislav Petkov wrote:
>>>>> So there are two questions here:
>>>>> 1. Is gov_queue_work() want to queue the work on offline cpu?
> 
> No. We are only working with online cpus now in cpufreq core and governors.
> 
>>> Besides, the cpu gov_queue_work() is using 'policy->cpus' which seems to
>>> be updated during UP DOWN notify, I think they are supposed to be online.
>>>
>>> But we need expert in cpufreq to confirm all these...
> 
> I confirm this. policy->cpus only contains online cpus.. and
> policy->related_cpus
> always contain online+offline cpus.

Nice to be confirmed :)

> 
>> And I guess this may help to reduce the chance to trigger WARN:
>>
>> diff --git a/drivers/cpufreq/cpufreq_governor.c
>> b/drivers/cpufreq/cpufreq_governor.c
>> index 443442d..0f96013 100644
>> --- a/drivers/cpufreq/cpufreq_governor.c
>> +++ b/drivers/cpufreq/cpufreq_governor.c
>> @@ -180,7 +180,7 @@ void gov_queue_work(struct dbs_data *dbs_data,
>> struct cpufreq_policy *policy,
>>         if (!all_cpus) {
>>                 __gov_queue_work(smp_processor_id(), dbs_data, delay);
>>         } else {
>> -               for_each_cpu(i, policy->cpus)
>> +               for_each_cpu_and(i, policy->cpus, cpu_online_mask)
>>                         __gov_queue_work(i, dbs_data, delay);
>>         }
>>  }
> 
> Not required at all... policy->cpus is guaranteed to have only online cpus.

Yeah, that's right, I guess the issue is, although the policy->cpus is
correct at a given time, after get cpu from it, it's possible to be
changed, unless we disabled preempt or irq, or hotplug before we use it...

Like such issue cases:
				get x from policy->cpus
	DOWN notifier
	change policy->cpus
	do offline x
				send ipi to x

Will that happen?

Regards,
Michael Wang


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> 

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Michael Wang]

On 05/20/2013 03:25 PM, Michael Wang wrote:
[]
> 
> Yeah, that's right, I guess the issue is, although the policy->cpus is
> correct at a given time, after get cpu from it, it's possible to be
> changed, unless we disabled preempt or irq, or hotplug before we use it...
> 
> Like such issue cases:
> 				get x from policy->cpus
> 	DOWN notifier
> 	change policy->cpus
> 	do offline x
> 				send ipi to x
> 
> Will that happen?

May be we could do some test to confirm it?

diff --git a/drivers/cpufreq/cpufreq_governor.c
b/drivers/cpufreq/cpufreq_governor.c
index 443442d..449be88 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -26,6 +26,7 @@
 #include <linux/tick.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
+#include <linux/cpu.h>

 #include "cpufreq_governor.h"

@@ -180,8 +181,10 @@ void gov_queue_work(struct dbs_data *dbs_data,
struct cpufreq_policy *policy,
        if (!all_cpus) {
                __gov_queue_work(smp_processor_id(), dbs_data, delay);
        } else {
+               get_online_cpus();
                for_each_cpu(i, policy->cpus)
                        __gov_queue_work(i, dbs_data, delay);
+               put_online_cpus();
        }
 }
 EXPORT_SYMBOL_GPL(gov_queue_work);

This is supposed to make WARN disappear, if it works, then BINGO :)

Regards,
Michael Wang

> 
> Regards,
> Michael Wang
> 
> 
>> --
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>>
> 
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> 

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Viresh Kumar]

On 20 May 2013 14:26, Michael Wang <wangyun@linux.vnet.ibm.com> wrote:
> On 05/20/2013 03:25 PM, Michael Wang wrote:
>> Yeah, that's right, I guess the issue is, although the policy->cpus is
>> correct at a given time, after get cpu from it, it's possible to be
>> changed, unless we disabled preempt or irq, or hotplug before we use it...
>>
>> Like such issue cases:
>>                               get x from policy->cpus
>>       DOWN notifier
>>       change policy->cpus
>>       do offline x
>>                               send ipi to x
>>
>> Will that happen?

Sorry I am not sure. :(

I can see mutex being used in cpufreq_governor.c which should take care
of race conditions...

> May be we could do some test to confirm it?
>
> diff --git a/drivers/cpufreq/cpufreq_governor.c
> b/drivers/cpufreq/cpufreq_governor.c
> index 443442d..449be88 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -26,6 +26,7 @@
>  #include <linux/tick.h>
>  #include <linux/types.h>
>  #include <linux/workqueue.h>
> +#include <linux/cpu.h>
>
>  #include "cpufreq_governor.h"
>
> @@ -180,8 +181,10 @@ void gov_queue_work(struct dbs_data *dbs_data,
> struct cpufreq_policy *policy,
>         if (!all_cpus) {
>                 __gov_queue_work(smp_processor_id(), dbs_data, delay);
>         } else {
> +               get_online_cpus();
>                 for_each_cpu(i, policy->cpus)
>                         __gov_queue_work(i, dbs_data, delay);
> +               put_online_cpus();
>         }
>  }
>  EXPORT_SYMBOL_GPL(gov_queue_work);
>
> This is supposed to make WARN disappear, if it works, then BINGO :)

Let people test it and then we can talk :)

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Michael Wang]

On 05/20/2013 05:09 PM, Viresh Kumar wrote:
> On 20 May 2013 14:26, Michael Wang <wangyun@linux.vnet.ibm.com> wrote:
>> On 05/20/2013 03:25 PM, Michael Wang wrote:
>>> Yeah, that's right, I guess the issue is, although the policy->cpus is
>>> correct at a given time, after get cpu from it, it's possible to be
>>> changed, unless we disabled preempt or irq, or hotplug before we use it...
>>>
>>> Like such issue cases:
>>>                               get x from policy->cpus
>>>       DOWN notifier
>>>       change policy->cpus
>>>       do offline x
>>>                               send ipi to x
>>>
>>> Will that happen?
> 
> Sorry I am not sure. :(
> 
> I can see mutex being used in cpufreq_governor.c which should take care
> of race conditions...
> 
>> May be we could do some test to confirm it?
>>
>> diff --git a/drivers/cpufreq/cpufreq_governor.c
>> b/drivers/cpufreq/cpufreq_governor.c
>> index 443442d..449be88 100644
>> --- a/drivers/cpufreq/cpufreq_governor.c
>> +++ b/drivers/cpufreq/cpufreq_governor.c
>> @@ -26,6 +26,7 @@
>>  #include <linux/tick.h>
>>  #include <linux/types.h>
>>  #include <linux/workqueue.h>
>> +#include <linux/cpu.h>
>>
>>  #include "cpufreq_governor.h"
>>
>> @@ -180,8 +181,10 @@ void gov_queue_work(struct dbs_data *dbs_data,
>> struct cpufreq_policy *policy,
>>         if (!all_cpus) {
>>                 __gov_queue_work(smp_processor_id(), dbs_data, delay);
>>         } else {
>> +               get_online_cpus();
>>                 for_each_cpu(i, policy->cpus)
>>                         __gov_queue_work(i, dbs_data, delay);
>> +               put_online_cpus();
>>         }
>>  }
>>  EXPORT_SYMBOL_GPL(gov_queue_work);
>>
>> This is supposed to make WARN disappear, if it works, then BINGO :)
> 
> Let people test it and then we can talk :)

Agree :)

Borislav, would you like to take a try?

If this fix cause other troubles, you could try get_cpu() or disable irq
also.

Regards,
Michael Wang

> 

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Srivatsa S. Bhat]

On 05/20/2013 01:40 PM, Frederic Weisbecker wrote:
> 2013/5/20 Borislav Petkov <bp@alien8.de>:
>> On Mon, May 20, 2013 at 11:16:33AM +0800, Michael Wang wrote:
>>> I suppose the reason is that the cpu we passed to
>>> mod_delayed_work_on() has a chance to become offline before we
>>> disabled irq, what about check it before send resched ipi? like:
>>
>> I think this is only addressing the symptoms - what we should be doing
>> instead is asking ourselves why are we even scheduling work on a cpu if
>> the machine goes offline?
>>
>> I don't know though who should be responsible for killing all that
>> work - the workqueue itself or the guy who created it, i.e. cpufreq
>> governor...
>>
>> Hmmm.
> 
> Let's look at this portion of cpu_down():
> 
> 	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> 	if (err) {
> 		/* CPU didn't die: tell everyone.  Can't complain. */
> 		smpboot_unpark_threads(cpu);
> 		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
> 		goto out_release;
> 	}
> 	BUG_ON(cpu_online(cpu));
> 
> 	/*
> 	 * The migration_call() CPU_DYING callback will have removed all
> 	 * runnable tasks from the cpu, there's only the idle task left now
> 	 * that the migration thread is done doing the stop_machine thing.
> 	 *
> 	 * Wait for the stop thread to go away.
> 	 */
> 	while (!idle_cpu(cpu))
> 		cpu_relax();
> 	/* This actually kills the CPU. */
> 	__cpu_die(cpu);
> 
> 	/* CPU is completely dead: tell everyone.  Too late to complain. */
> 	cpu_notify_nofail(CPU_DEAD | mod, hcpu);
> 
> 	check_for_tasks(cpu);
> 
> The CPU is considered offline after the take_cpu_down stop machine job
> completes. But the struct timer_list timers are migrated later through
> CPU_DEAD notification. Only once that's completed we check for illegal
> residual tasks in the CPU.  So there is a little window between the
> stop machine thing and __cpu_die() where a timer can fire with
> cpu_online(cpu) == 1.
> 

Nope, the dying CPU is removed from the cpu_online_mask in the very first
stages of stop_machine(), specifically in the __cpu_disable() function.
__cpu_die() is just a dummy.

> Now concerning the workqueue I don't know. I guess the per cpu ones
> are not migrated due to their affinity. Apparently they can still wake
> up and execute works due to the timers...

The interesting thing is that the cpufreq governor actually _cancels_ the
queued work in CPU_DOWN_PREPARE stage, as far as I understand.

cpufreq_cpu_callback()
  -> __cpufreq_remove_dev()
    -> __cpufreq_governor(data, CPUFREQ_GOV_STOP);
      -> od_cpufreq_governor_dbs()
	 -> cpufreq_governor_dbs(), which has the following case statement:


        case CPUFREQ_GOV_STOP:
                if (dbs_data->cdata->governor == GOV_CONSERVATIVE)
                        cs_dbs_info->enable = 0;

                gov_cancel_work(dbs_data, policy);

                mutex_lock(&dbs_data->mutex);
                mutex_destroy(&cpu_cdbs->timer_mutex);

                mutex_unlock(&dbs_data->mutex);

                break;


But recently I removed the call to __cpufreq_remove_dev() in the suspend/resume
path (tasks frozen), in commit a66b2e503 (cpufreq: Preserve sysfs files across
suspend/resume). So I'm curious to know if this is affecting in any way.

So Boris, do you see the warnings during regular hotplug also (via sysfs) or
only during suspend/shutdown? [Actually shutdown doesn't freeze tasks, so that is
already a hint that this warning can be triggered via sysfs also, but it would
be good to get a confirmation.]

And Viresh, in the regular hotplug paths, the call to gov_cancel_work() is
supposed to kill any pending workqueue functions pertaining to offline CPUs
right? Could there be a synchronization bug somewhere due to which this
might not be happening properly?

Regards,
Srivatsa S. Bhat

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Viresh Kumar]

On 20 May 2013 15:01, Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> wrote:
> And Viresh, in the regular hotplug paths, the call to gov_cancel_work() is
> supposed to kill any pending workqueue functions pertaining to offline CPUs
> right?

Yes.. It will cancel work for all cpus first and will start again for
online cpus again.

> Could there be a synchronization bug somewhere due to which this
> might not be happening properly?

Not sure.. I have seen mutex's are used well in cpufreq_governor.. don't know
if I missed something.

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Viresh Kumar]

On 20 May 2013 15:10, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> On 20 May 2013 15:01, Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> wrote:
>> And Viresh, in the regular hotplug paths, the call to gov_cancel_work() is
>> supposed to kill any pending workqueue functions pertaining to offline CPUs
>> right?
>
> Yes.. It will cancel work for all cpus first and will start again for
> online cpus again.
>
>> Could there be a synchronization bug somewhere due to which this
>> might not be happening properly?
>
> Not sure.. I have seen mutex's are used well in cpufreq_governor.. don't know
> if I missed something.

Borislav,

Can you try below change to see if the issue is still present? (Untested)

diff --git a/drivers/cpufreq/cpufreq_governor.c
b/drivers/cpufreq/cpufreq_governor.c
index 7532570..b9ae5f6 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -359,7 +359,9 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                if (dbs_data->cdata->governor == GOV_CONSERVATIVE)
                        cs_dbs_info->enable = 0;

+               mutex_lock(&cpu_cdbs->timer_mutex);
                gov_cancel_work(dbs_data, policy);
+               mutex_unlock(&cpu_cdbs->timer_mutex);

                mutex_lock(&dbs_data->mutex);
                mutex_destroy(&cpu_cdbs->timer_mutex);

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Borislav Petkov]

On Mon, May 20, 2013 at 05:24:05PM +0800, Michael Wang wrote:
> >> diff --git a/drivers/cpufreq/cpufreq_governor.c
> >> b/drivers/cpufreq/cpufreq_governor.c
> >> index 443442d..449be88 100644
> >> --- a/drivers/cpufreq/cpufreq_governor.c
> >> +++ b/drivers/cpufreq/cpufreq_governor.c
> >> @@ -26,6 +26,7 @@
> >>  #include <linux/tick.h>
> >>  #include <linux/types.h>
> >>  #include <linux/workqueue.h>
> >> +#include <linux/cpu.h>
> >>
> >>  #include "cpufreq_governor.h"
> >>
> >> @@ -180,8 +181,10 @@ void gov_queue_work(struct dbs_data *dbs_data,
> >> struct cpufreq_policy *policy,
> >>         if (!all_cpus) {
> >>                 __gov_queue_work(smp_processor_id(), dbs_data, delay);
> >>         } else {
> >> +               get_online_cpus();
> >>                 for_each_cpu(i, policy->cpus)
> >>                         __gov_queue_work(i, dbs_data, delay);
> >> +               put_online_cpus();
> >>         }
> >>  }
> >>  EXPORT_SYMBOL_GPL(gov_queue_work);
> >>
> >> This is supposed to make WARN disappear, if it works, then BINGO :)
> > 
> > Let people test it and then we can talk :)
> 
> Agree :)
> 
> Borislav, would you like to take a try?
> 
> If this fix cause other troubles, you could try get_cpu() or disable irq
> also.

I just confirmed that policy->cpus contains offlined cores with this:

diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 5af40ad82d23..e8c25f71e9b6 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -169,6 +169,9 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
 {
        struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
 
+       if (WARN_ON(!cpu_online(cpu)))
+               return;
+
        mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
 }

see splats collection below.

And I don't think your fix above addresses the issue for the simple
reason that if cpus go offline *before* you do get_online_cpus(), then
policy->cpus will already contain offlined cpus.

Rather, a better fix would be, IMHO, to do this (it works here, of course):

---
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 5af40ad82d23..58541b164494 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -17,6 +17,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <asm/cputime.h>
+#include <linux/cpu.h>
 #include <linux/cpufreq.h>
 #include <linux/cpumask.h>
 #include <linux/export.h>
@@ -169,7 +170,15 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
 {
        struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
 
+       get_online_cpus();
+
+       if (!cpu_online(cpu))
+               goto out;
+
        mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
+
+ out:
+       put_online_cpus();
 }
 
 void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
--


[   94.386340] EXT4-fs (sda7): re-mounted. Opts: (null)
[   96.520362] kvm: exiting hardware virtualization
[   96.637687] ACPI: Preparing to enter system sleep state S5
[   96.643506] Disabling non-boot CPUs ...
[   96.855499] ------------[ cut here ]------------
[   96.860172] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
[   96.868501] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
[   96.914238] CPU: 0 PID: 315 Comm: kworker/1:2 Tainted: G        W    3.10.0-rc1+ #2
[   96.921969] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
[   96.929424] Workqueue: events od_dbs_timer
[   96.933574]  0000000000000009 ffff88043a08bc78 ffffffff8161445c ffff88043a08bcb8
[   96.941085]  ffffffff8103e540 ffff88043b712a80 0000000000000001 ffff88043a296400
[   96.948602]  ffff88043b712a80 ffffffff81cdc910 0000000000000001 ffff88043a08bcc8
[   96.956123] Call Trace:
[   96.958602]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
[   96.963801]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
[   96.969858]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
[   96.975735]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
[   96.981359]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
[   96.986808]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
[   96.992691]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
[   96.998756]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
[   97.004371]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
[   97.010256]  [<ffffffff8106634a>] kthread+0xea/0xf0
[   97.015185]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.021605]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
[   97.027049]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.033457] ---[ end trace d36d91c626ac81a0 ]---
[   97.039221] ------------[ cut here ]------------
[   97.039227] ------------[ cut here ]------------
[   97.039229] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
[   97.039243] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
[   97.039245] CPU: 4 PID: 82 Comm: kworker/2:1 Tainted: G        W    3.10.0-rc1+ #2
[   97.039245] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
[   97.039248] Workqueue: events od_dbs_timer
[   97.039250]  0000000000000009 ffff88043b5cfc78 ffffffff8161445c ffff88043b5cfcb8
[   97.039251]  ffffffff8103e540 ffff88043b712a80 0000000000000002 ffff88043a295e00
[   97.039253]  ffff88043b712a80 ffffffff81cdc910 0000000000000002 ffff88043b5cfcc8
[   97.039253] Call Trace:
[   97.039255]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
[   97.039257]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
[   97.039258]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
[   97.039259]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
[   97.039261]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
[   97.039263]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
[   97.039264]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
[   97.039265]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
[   97.039267]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
[   97.039268]  [<ffffffff8106634a>] kthread+0xea/0xf0
[   97.039269]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.039270]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
[   97.039272]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.039272] ---[ end trace d36d91c626ac81a1 ]---
[   97.143214] nouveau E[     DRM] GPU lockup - switching to software fbcon
[   97.318430] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
[   97.326804] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
[   97.374578] CPU: 0 PID: 98 Comm: kworker/3:1 Tainted: G        W    3.10.0-rc1+ #2
[   97.384154] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
[   97.393566] Workqueue: events od_dbs_timer
[   97.399675]  0000000000000009 ffff88043b179c78 ffffffff8161445c ffff88043b179cb8
[   97.409153]  ffffffff8103e540 ffff88043b712a80 0000000000000003 ffff88043a295a00
[   97.418623]  ffff88043b712a80 ffffffff81cdc910 0000000000000003 ffff88043b179cc8
[   97.428103] Call Trace:
[   97.432520]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
[   97.439678]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
[   97.447694]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
[   97.455512]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
[   97.462993]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
[   97.470259]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
[   97.477878]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
[   97.485652]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
[   97.492969]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
[   97.500565]  [<ffffffff8106634a>] kthread+0xea/0xf0
[   97.507167]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.515255]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
[   97.522389]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.530472] ---[ end trace d36d91c626ac81a2 ]---
[   97.543176] ------------[ cut here ]------------
[   97.547172] ------------[ cut here ]------------
[   97.547178] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
[   97.547197] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
[   97.547199] CPU: 7 PID: 316 Comm: kworker/5:1 Tainted: G        W    3.10.0-rc1+ #2
[   97.547200] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
[   97.547202] Workqueue: events od_dbs_timer
[   97.547204]  0000000000000009 ffff88043905dc78 ffffffff8161445c ffff88043905dcb8
[   97.547205]  ffffffff8103e540 ffff88043b712a80 0000000000000005 ffff88043a295800
[   97.547206]  ffff88043b712a80 ffffffff81cdc910 0000000000000005 ffff88043905dcc8
[   97.547207] Call Trace:
[   97.547211]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
[   97.547214]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
[   97.547215]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
[   97.547216]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
[   97.547218]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
[   97.547220]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
[   97.547221]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
[   97.547222]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
[   97.547224]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
[   97.547225]  [<ffffffff8106634a>] kthread+0xea/0xf0
[   97.547226]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.547228]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
[   97.547229]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.547230] ---[ end trace d36d91c626ac81a3 ]---
[   97.761326] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
[   97.770798] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
[   97.819617] CPU: 0 PID: 253 Comm: kworker/4:1 Tainted: G        W    3.10.0-rc1+ #2
[   97.828623] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
[   97.837372] Workqueue: events od_dbs_timer
[   97.842805]  0000000000000009 ffff880439529c78 ffffffff8161445c ffff880439529cb8
[   97.851628]  ffffffff8103e540 ffff88043b712a80 0000000000000004 ffff88043a295c00
[   97.860445]  ffff88043b712a80 ffffffff81cdc910 0000000000000004 ffff880439529cc8
[   97.869249] Call Trace:
[   97.873041]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
[   97.879533]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
[   97.886912]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
[   97.894100]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
[   97.901002]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
[   97.907706]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
[   97.914797]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
[   97.922016]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
[   97.928803]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
[   97.935837]  [<ffffffff8106634a>] kthread+0xea/0xf0
[   97.941900]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.949443]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
[   97.956027]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   97.963563] ---[ end trace d36d91c626ac81a4 ]---
[   97.970449] ------------[ cut here ]------------
[   97.976277] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
[   97.985762] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
[   98.035051] CPU: 0 PID: 102 Comm: kworker/6:1 Tainted: G        W    3.10.0-rc1+ #2
[   98.044067] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
[   98.052834] Workqueue: events od_dbs_timer
[   98.058285]  0000000000000009 ffff88043b6f3c78 ffffffff8161445c ffff88043b6f3cb8
[   98.067114]  ffffffff8103e540 ffff88043b712a80 0000000000000006 ffff88043a295600
[   98.075924]  ffff88043b712a80 ffffffff81cdc910 0000000000000006 ffff88043b6f3cc8
[   98.084735] Call Trace:
[   98.088518]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
[   98.095024]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
[   98.102386]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
[   98.109565]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
[   98.116502]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
[   98.123253]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
[   98.130394]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
[   98.137667]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
[   98.144456]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
[   98.151510]  [<ffffffff8106634a>] kthread+0xea/0xf0
[   98.157583]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   98.165143]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
[   98.171730]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   98.179282] ---[ end trace d36d91c626ac81a5 ]---
[   98.185098] ------------[ cut here ]------------
[   98.190903] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
[   98.200387] Modules linked in: ext2 vfat fat loop
[   98.205029] nouveau W[   PFIFO][0000:03:00.0] unknown intr 0x00400000, ch 1
[   98.214563]  usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
[   98.258886] CPU: 0 PID: 318 Comm: kworker/7:1 Tainted: G        W    3.10.0-rc1+ #2
[   98.267919] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
[   98.276689] Workqueue: events od_dbs_timer
[   98.282147]  0000000000000009 ffff88043969dc78 ffffffff8161445c ffff88043969dcb8
[   98.290991]  ffffffff8103e540 ffff88043b712a80 0000000000000007 ffff88043a295200
[   98.299832]  ffff88043b712a80 ffffffff81cdc910 0000000000000007 ffff88043969dcc8
[   98.308671] Call Trace:
[   98.312471]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
[   98.318982]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
[   98.326376]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
[   98.333577]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
[   98.340482]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
[   98.347160]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
[   98.354232]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
[   98.361471]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
[   98.368260]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
[   98.375309]  [<ffffffff8106634a>] kthread+0xea/0xf0
[   98.381385]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   98.388951]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
[   98.395546]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
[   98.403097] ---[ end trace d36d91c626ac81a6 ]---
[   98.409180] Power down.
[   98.413109] acpi_power_off called

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Viresh Kumar]

On 20 May 2013 18:53, Borislav Petkov <bp@alien8.de> wrote:
> I just confirmed that policy->cpus contains offlined cores with this:
>
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index 5af40ad82d23..e8c25f71e9b6 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -169,6 +169,9 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
>  {
>         struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
>
> +       if (WARN_ON(!cpu_online(cpu)))
> +               return;
> +
>         mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
>  }

Hmm, so for sure there is some locking issue there.
Have you tried my patch? I am not sure if it will fix everything but may
fix it.

> see splats collection below.
>
> And I don't think your fix above addresses the issue for the simple
> reason that if cpus go offline *before* you do get_online_cpus(), then
> policy->cpus will already contain offlined cpus.
>
> Rather, a better fix would be, IMHO, to do this (it works here, of course):
>
> ---
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index 5af40ad82d23..58541b164494 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -17,6 +17,7 @@
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>
>  #include <asm/cputime.h>
> +#include <linux/cpu.h>
>  #include <linux/cpufreq.h>
>  #include <linux/cpumask.h>
>  #include <linux/export.h>
> @@ -169,7 +170,15 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
>  {
>         struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
>
> +       get_online_cpus();
> +
> +       if (!cpu_online(cpu))
> +               goto out;
> +
>         mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
> +
> + out:
> +       put_online_cpus();
>  }
>
>  void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,

This looks fine, but I want to fix the locking rather than just
hiding the issue. :)

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Borislav Petkov]

On Mon, May 20, 2013 at 07:13:08PM +0530, Viresh Kumar wrote:
> Hmm, so for sure there is some locking issue there. ave you tried my
> Hpatch?

No, not yet. Pretty busy ATM. Btw, you could try reproducing it too, in
the meantime - simply enable

CONFIG_NO_HZ_COMMON=y
# CONFIG_NO_HZ_IDLE is not set
CONFIG_NO_HZ_FULL=y
CONFIG_NO_HZ_FULL_ALL=y
CONFIG_NO_HZ=y
CONFIG_RCU_FAST_NO_HZ=y

and halt the box. I don't know whether !x86 boxen support NO_HZ_FULL yet
though.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Michael Wang]

On 05/20/2013 09:23 PM, Borislav Petkov wrote:
> On Mon, May 20, 2013 at 05:24:05PM +0800, Michael Wang wrote:
>>>> diff --git a/drivers/cpufreq/cpufreq_governor.c
>>>> b/drivers/cpufreq/cpufreq_governor.c
>>>> index 443442d..449be88 100644
>>>> --- a/drivers/cpufreq/cpufreq_governor.c
>>>> +++ b/drivers/cpufreq/cpufreq_governor.c
>>>> @@ -26,6 +26,7 @@
>>>>  #include <linux/tick.h>
>>>>  #include <linux/types.h>
>>>>  #include <linux/workqueue.h>
>>>> +#include <linux/cpu.h>
>>>>
>>>>  #include "cpufreq_governor.h"
>>>>
>>>> @@ -180,8 +181,10 @@ void gov_queue_work(struct dbs_data *dbs_data,
>>>> struct cpufreq_policy *policy,
>>>>         if (!all_cpus) {
>>>>                 __gov_queue_work(smp_processor_id(), dbs_data, delay);
>>>>         } else {
>>>> +               get_online_cpus();
>>>>                 for_each_cpu(i, policy->cpus)
>>>>                         __gov_queue_work(i, dbs_data, delay);
>>>> +               put_online_cpus();
>>>>         }
>>>>  }
>>>>  EXPORT_SYMBOL_GPL(gov_queue_work);
>>>>
>>>> This is supposed to make WARN disappear, if it works, then BINGO :)
>>>
>>> Let people test it and then we can talk :)
>>
>> Agree :)
>>
>> Borislav, would you like to take a try?
>>
>> If this fix cause other troubles, you could try get_cpu() or disable irq
>> also.
> 
> I just confirmed that policy->cpus contains offlined cores with this:
> 
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index 5af40ad82d23..e8c25f71e9b6 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -169,6 +169,9 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
>  {
>         struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
> 
> +       if (WARN_ON(!cpu_online(cpu)))
> +               return;
> +

This is not enough to prove that policy->cpus is wrong, the cpu could be
online when get from policy->cpus, but offline when checked here, since
hotplug is able to happen during the period.

>         mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
>  }
> 
> see splats collection below.
> 
> And I don't think your fix above addresses the issue for the simple
> reason that if cpus go offline *before* you do get_online_cpus(), then
> policy->cpus will already contain offlined cpus.

I don't get it...

get_online_cpus() is just stop hotplug happen after it was invoked, so
unless policy->cpus is really wrong, otherwise all the cpu it masked
won't go offline any more.

> 
> Rather, a better fix would be, IMHO, to do this (it works here, of course):
> 
> ---
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index 5af40ad82d23..58541b164494 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -17,6 +17,7 @@
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> 
>  #include <asm/cputime.h>
> +#include <linux/cpu.h>
>  #include <linux/cpufreq.h>
>  #include <linux/cpumask.h>
>  #include <linux/export.h>
> @@ -169,7 +170,15 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
>  {
>         struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
> 
> +       get_online_cpus();

This protect nothing...before we go here, the cpu could already offline,
nothing changed...

If you really want to confirm the policy->cpus was wrong, the way should
be apply the fix I suggested, than check online in here.

If hotplug could not happen but still get an offline cpu from
policy->cpus, than we could say it's wrong, otherwise we proved nothing...

Regards,
Michael Wang

> +
> +       if (!cpu_online(cpu))
> +               goto out;
> +
>         mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
> +
> + out:
> +       put_online_cpus();
>  }
> 
>  void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
> --
> 
> 
> [   94.386340] EXT4-fs (sda7): re-mounted. Opts: (null)
> [   96.520362] kvm: exiting hardware virtualization
> [   96.637687] ACPI: Preparing to enter system sleep state S5
> [   96.643506] Disabling non-boot CPUs ...
> [   96.855499] ------------[ cut here ]------------
> [   96.860172] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
> [   96.868501] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
> [   96.914238] CPU: 0 PID: 315 Comm: kworker/1:2 Tainted: G        W    3.10.0-rc1+ #2
> [   96.921969] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
> [   96.929424] Workqueue: events od_dbs_timer
> [   96.933574]  0000000000000009 ffff88043a08bc78 ffffffff8161445c ffff88043a08bcb8
> [   96.941085]  ffffffff8103e540 ffff88043b712a80 0000000000000001 ffff88043a296400
> [   96.948602]  ffff88043b712a80 ffffffff81cdc910 0000000000000001 ffff88043a08bcc8
> [   96.956123] Call Trace:
> [   96.958602]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
> [   96.963801]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
> [   96.969858]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
> [   96.975735]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
> [   96.981359]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
> [   96.986808]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
> [   96.992691]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
> [   96.998756]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
> [   97.004371]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
> [   97.010256]  [<ffffffff8106634a>] kthread+0xea/0xf0
> [   97.015185]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.021605]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
> [   97.027049]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.033457] ---[ end trace d36d91c626ac81a0 ]---
> [   97.039221] ------------[ cut here ]------------
> [   97.039227] ------------[ cut here ]------------
> [   97.039229] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
> [   97.039243] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
> [   97.039245] CPU: 4 PID: 82 Comm: kworker/2:1 Tainted: G        W    3.10.0-rc1+ #2
> [   97.039245] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
> [   97.039248] Workqueue: events od_dbs_timer
> [   97.039250]  0000000000000009 ffff88043b5cfc78 ffffffff8161445c ffff88043b5cfcb8
> [   97.039251]  ffffffff8103e540 ffff88043b712a80 0000000000000002 ffff88043a295e00
> [   97.039253]  ffff88043b712a80 ffffffff81cdc910 0000000000000002 ffff88043b5cfcc8
> [   97.039253] Call Trace:
> [   97.039255]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
> [   97.039257]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
> [   97.039258]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
> [   97.039259]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
> [   97.039261]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
> [   97.039263]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
> [   97.039264]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
> [   97.039265]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
> [   97.039267]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
> [   97.039268]  [<ffffffff8106634a>] kthread+0xea/0xf0
> [   97.039269]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.039270]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
> [   97.039272]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.039272] ---[ end trace d36d91c626ac81a1 ]---
> [   97.143214] nouveau E[     DRM] GPU lockup - switching to software fbcon
> [   97.318430] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
> [   97.326804] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
> [   97.374578] CPU: 0 PID: 98 Comm: kworker/3:1 Tainted: G        W    3.10.0-rc1+ #2
> [   97.384154] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
> [   97.393566] Workqueue: events od_dbs_timer
> [   97.399675]  0000000000000009 ffff88043b179c78 ffffffff8161445c ffff88043b179cb8
> [   97.409153]  ffffffff8103e540 ffff88043b712a80 0000000000000003 ffff88043a295a00
> [   97.418623]  ffff88043b712a80 ffffffff81cdc910 0000000000000003 ffff88043b179cc8
> [   97.428103] Call Trace:
> [   97.432520]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
> [   97.439678]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
> [   97.447694]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
> [   97.455512]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
> [   97.462993]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
> [   97.470259]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
> [   97.477878]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
> [   97.485652]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
> [   97.492969]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
> [   97.500565]  [<ffffffff8106634a>] kthread+0xea/0xf0
> [   97.507167]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.515255]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
> [   97.522389]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.530472] ---[ end trace d36d91c626ac81a2 ]---
> [   97.543176] ------------[ cut here ]------------
> [   97.547172] ------------[ cut here ]------------
> [   97.547178] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
> [   97.547197] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
> [   97.547199] CPU: 7 PID: 316 Comm: kworker/5:1 Tainted: G        W    3.10.0-rc1+ #2
> [   97.547200] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
> [   97.547202] Workqueue: events od_dbs_timer
> [   97.547204]  0000000000000009 ffff88043905dc78 ffffffff8161445c ffff88043905dcb8
> [   97.547205]  ffffffff8103e540 ffff88043b712a80 0000000000000005 ffff88043a295800
> [   97.547206]  ffff88043b712a80 ffffffff81cdc910 0000000000000005 ffff88043905dcc8
> [   97.547207] Call Trace:
> [   97.547211]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
> [   97.547214]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
> [   97.547215]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
> [   97.547216]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
> [   97.547218]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
> [   97.547220]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
> [   97.547221]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
> [   97.547222]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
> [   97.547224]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
> [   97.547225]  [<ffffffff8106634a>] kthread+0xea/0xf0
> [   97.547226]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.547228]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
> [   97.547229]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.547230] ---[ end trace d36d91c626ac81a3 ]---
> [   97.761326] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
> [   97.770798] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
> [   97.819617] CPU: 0 PID: 253 Comm: kworker/4:1 Tainted: G        W    3.10.0-rc1+ #2
> [   97.828623] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
> [   97.837372] Workqueue: events od_dbs_timer
> [   97.842805]  0000000000000009 ffff880439529c78 ffffffff8161445c ffff880439529cb8
> [   97.851628]  ffffffff8103e540 ffff88043b712a80 0000000000000004 ffff88043a295c00
> [   97.860445]  ffff88043b712a80 ffffffff81cdc910 0000000000000004 ffff880439529cc8
> [   97.869249] Call Trace:
> [   97.873041]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
> [   97.879533]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
> [   97.886912]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
> [   97.894100]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
> [   97.901002]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
> [   97.907706]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
> [   97.914797]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
> [   97.922016]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
> [   97.928803]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
> [   97.935837]  [<ffffffff8106634a>] kthread+0xea/0xf0
> [   97.941900]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.949443]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
> [   97.956027]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   97.963563] ---[ end trace d36d91c626ac81a4 ]---
> [   97.970449] ------------[ cut here ]------------
> [   97.976277] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
> [   97.985762] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
> [   98.035051] CPU: 0 PID: 102 Comm: kworker/6:1 Tainted: G        W    3.10.0-rc1+ #2
> [   98.044067] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
> [   98.052834] Workqueue: events od_dbs_timer
> [   98.058285]  0000000000000009 ffff88043b6f3c78 ffffffff8161445c ffff88043b6f3cb8
> [   98.067114]  ffffffff8103e540 ffff88043b712a80 0000000000000006 ffff88043a295600
> [   98.075924]  ffff88043b712a80 ffffffff81cdc910 0000000000000006 ffff88043b6f3cc8
> [   98.084735] Call Trace:
> [   98.088518]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
> [   98.095024]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
> [   98.102386]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
> [   98.109565]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
> [   98.116502]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
> [   98.123253]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
> [   98.130394]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
> [   98.137667]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
> [   98.144456]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
> [   98.151510]  [<ffffffff8106634a>] kthread+0xea/0xf0
> [   98.157583]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   98.165143]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
> [   98.171730]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   98.179282] ---[ end trace d36d91c626ac81a5 ]---
> [   98.185098] ------------[ cut here ]------------
> [   98.190903] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
> [   98.200387] Modules linked in: ext2 vfat fat loop
> [   98.205029] nouveau W[   PFIFO][0000:03:00.0] unknown intr 0x00400000, ch 1
> [   98.214563]  usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
> [   98.258886] CPU: 0 PID: 318 Comm: kworker/7:1 Tainted: G        W    3.10.0-rc1+ #2
> [   98.267919] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
> [   98.276689] Workqueue: events od_dbs_timer
> [   98.282147]  0000000000000009 ffff88043969dc78 ffffffff8161445c ffff88043969dcb8
> [   98.290991]  ffffffff8103e540 ffff88043b712a80 0000000000000007 ffff88043a295200
> [   98.299832]  ffff88043b712a80 ffffffff81cdc910 0000000000000007 ffff88043969dcc8
> [   98.308671] Call Trace:
> [   98.312471]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
> [   98.318982]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
> [   98.326376]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
> [   98.333577]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
> [   98.340482]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
> [   98.347160]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
> [   98.354232]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
> [   98.361471]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
> [   98.368260]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
> [   98.375309]  [<ffffffff8106634a>] kthread+0xea/0xf0
> [   98.381385]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   98.388951]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
> [   98.395546]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
> [   98.403097] ---[ end trace d36d91c626ac81a6 ]---
> [   98.409180] Power down.
> [   98.413109] acpi_power_off called
> 

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Michael Wang]

On 05/21/2013 10:20 AM, Michael Wang wrote:
[snip]
> 
> If hotplug could not happen but still get an offline cpu from
> policy->cpus, than we could say it's wrong, otherwise we proved nothing...

like this:

diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 443442d..8ed8b35 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -26,6 +26,7 @@
 #include <linux/tick.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
+#include <linux/cpu.h>
 
 #include "cpufreq_governor.h"
 
@@ -169,6 +170,9 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
 {
        struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
 
+       if (WARN_ON(!cpu_online(cpu)))
+               return;
+
        mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
 }
 
@@ -180,8 +184,10 @@ void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
        if (!all_cpus) {
                __gov_queue_work(smp_processor_id(), dbs_data, delay);
        } else {
+               get_online_cpus();
                for_each_cpu(i, policy->cpus)
                        __gov_queue_work(i, dbs_data, delay);
+               put_online_cpus();
        }
 }
 EXPORT_SYMBOL_GPL(gov_queue_work);



Would you like to try it and see whether we trigger any WARN?

If still trigger WARN, then we could make sure the problem is
the wrong 'policy->cpus' ;-)

Regards,
Michael Wang

> 
> Regards,
> Michael Wang
> 
>> +
>> +       if (!cpu_online(cpu))
>> +               goto out;
>> +
>>         mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
>> +
>> + out:
>> +       put_online_cpus();
>>  }
>>
>>  void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
>> --
>>
>>
>> [   94.386340] EXT4-fs (sda7): re-mounted. Opts: (null)
>> [   96.520362] kvm: exiting hardware virtualization
>> [   96.637687] ACPI: Preparing to enter system sleep state S5
>> [   96.643506] Disabling non-boot CPUs ...
>> [   96.855499] ------------[ cut here ]------------
>> [   96.860172] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
>> [   96.868501] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
>> [   96.914238] CPU: 0 PID: 315 Comm: kworker/1:2 Tainted: G        W    3.10.0-rc1+ #2
>> [   96.921969] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
>> [   96.929424] Workqueue: events od_dbs_timer
>> [   96.933574]  0000000000000009 ffff88043a08bc78 ffffffff8161445c ffff88043a08bcb8
>> [   96.941085]  ffffffff8103e540 ffff88043b712a80 0000000000000001 ffff88043a296400
>> [   96.948602]  ffff88043b712a80 ffffffff81cdc910 0000000000000001 ffff88043a08bcc8
>> [   96.956123] Call Trace:
>> [   96.958602]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
>> [   96.963801]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
>> [   96.969858]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
>> [   96.975735]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
>> [   96.981359]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
>> [   96.986808]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
>> [   96.992691]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
>> [   96.998756]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
>> [   97.004371]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
>> [   97.010256]  [<ffffffff8106634a>] kthread+0xea/0xf0
>> [   97.015185]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.021605]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
>> [   97.027049]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.033457] ---[ end trace d36d91c626ac81a0 ]---
>> [   97.039221] ------------[ cut here ]------------
>> [   97.039227] ------------[ cut here ]------------
>> [   97.039229] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
>> [   97.039243] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
>> [   97.039245] CPU: 4 PID: 82 Comm: kworker/2:1 Tainted: G        W    3.10.0-rc1+ #2
>> [   97.039245] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
>> [   97.039248] Workqueue: events od_dbs_timer
>> [   97.039250]  0000000000000009 ffff88043b5cfc78 ffffffff8161445c ffff88043b5cfcb8
>> [   97.039251]  ffffffff8103e540 ffff88043b712a80 0000000000000002 ffff88043a295e00
>> [   97.039253]  ffff88043b712a80 ffffffff81cdc910 0000000000000002 ffff88043b5cfcc8
>> [   97.039253] Call Trace:
>> [   97.039255]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
>> [   97.039257]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
>> [   97.039258]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
>> [   97.039259]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
>> [   97.039261]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
>> [   97.039263]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
>> [   97.039264]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
>> [   97.039265]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
>> [   97.039267]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
>> [   97.039268]  [<ffffffff8106634a>] kthread+0xea/0xf0
>> [   97.039269]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.039270]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
>> [   97.039272]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.039272] ---[ end trace d36d91c626ac81a1 ]---
>> [   97.143214] nouveau E[     DRM] GPU lockup - switching to software fbcon
>> [   97.318430] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
>> [   97.326804] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
>> [   97.374578] CPU: 0 PID: 98 Comm: kworker/3:1 Tainted: G        W    3.10.0-rc1+ #2
>> [   97.384154] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
>> [   97.393566] Workqueue: events od_dbs_timer
>> [   97.399675]  0000000000000009 ffff88043b179c78 ffffffff8161445c ffff88043b179cb8
>> [   97.409153]  ffffffff8103e540 ffff88043b712a80 0000000000000003 ffff88043a295a00
>> [   97.418623]  ffff88043b712a80 ffffffff81cdc910 0000000000000003 ffff88043b179cc8
>> [   97.428103] Call Trace:
>> [   97.432520]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
>> [   97.439678]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
>> [   97.447694]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
>> [   97.455512]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
>> [   97.462993]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
>> [   97.470259]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
>> [   97.477878]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
>> [   97.485652]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
>> [   97.492969]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
>> [   97.500565]  [<ffffffff8106634a>] kthread+0xea/0xf0
>> [   97.507167]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.515255]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
>> [   97.522389]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.530472] ---[ end trace d36d91c626ac81a2 ]---
>> [   97.543176] ------------[ cut here ]------------
>> [   97.547172] ------------[ cut here ]------------
>> [   97.547178] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
>> [   97.547197] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
>> [   97.547199] CPU: 7 PID: 316 Comm: kworker/5:1 Tainted: G        W    3.10.0-rc1+ #2
>> [   97.547200] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
>> [   97.547202] Workqueue: events od_dbs_timer
>> [   97.547204]  0000000000000009 ffff88043905dc78 ffffffff8161445c ffff88043905dcb8
>> [   97.547205]  ffffffff8103e540 ffff88043b712a80 0000000000000005 ffff88043a295800
>> [   97.547206]  ffff88043b712a80 ffffffff81cdc910 0000000000000005 ffff88043905dcc8
>> [   97.547207] Call Trace:
>> [   97.547211]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
>> [   97.547214]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
>> [   97.547215]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
>> [   97.547216]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
>> [   97.547218]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
>> [   97.547220]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
>> [   97.547221]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
>> [   97.547222]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
>> [   97.547224]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
>> [   97.547225]  [<ffffffff8106634a>] kthread+0xea/0xf0
>> [   97.547226]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.547228]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
>> [   97.547229]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.547230] ---[ end trace d36d91c626ac81a3 ]---
>> [   97.761326] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
>> [   97.770798] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
>> [   97.819617] CPU: 0 PID: 253 Comm: kworker/4:1 Tainted: G        W    3.10.0-rc1+ #2
>> [   97.828623] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
>> [   97.837372] Workqueue: events od_dbs_timer
>> [   97.842805]  0000000000000009 ffff880439529c78 ffffffff8161445c ffff880439529cb8
>> [   97.851628]  ffffffff8103e540 ffff88043b712a80 0000000000000004 ffff88043a295c00
>> [   97.860445]  ffff88043b712a80 ffffffff81cdc910 0000000000000004 ffff880439529cc8
>> [   97.869249] Call Trace:
>> [   97.873041]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
>> [   97.879533]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
>> [   97.886912]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
>> [   97.894100]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
>> [   97.901002]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
>> [   97.907706]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
>> [   97.914797]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
>> [   97.922016]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
>> [   97.928803]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
>> [   97.935837]  [<ffffffff8106634a>] kthread+0xea/0xf0
>> [   97.941900]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.949443]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
>> [   97.956027]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   97.963563] ---[ end trace d36d91c626ac81a4 ]---
>> [   97.970449] ------------[ cut here ]------------
>> [   97.976277] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
>> [   97.985762] Modules linked in: ext2 vfat fat loop usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
>> [   98.035051] CPU: 0 PID: 102 Comm: kworker/6:1 Tainted: G        W    3.10.0-rc1+ #2
>> [   98.044067] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
>> [   98.052834] Workqueue: events od_dbs_timer
>> [   98.058285]  0000000000000009 ffff88043b6f3c78 ffffffff8161445c ffff88043b6f3cb8
>> [   98.067114]  ffffffff8103e540 ffff88043b712a80 0000000000000006 ffff88043a295600
>> [   98.075924]  ffff88043b712a80 ffffffff81cdc910 0000000000000006 ffff88043b6f3cc8
>> [   98.084735] Call Trace:
>> [   98.088518]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
>> [   98.095024]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
>> [   98.102386]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
>> [   98.109565]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
>> [   98.116502]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
>> [   98.123253]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
>> [   98.130394]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
>> [   98.137667]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
>> [   98.144456]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
>> [   98.151510]  [<ffffffff8106634a>] kthread+0xea/0xf0
>> [   98.157583]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   98.165143]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
>> [   98.171730]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   98.179282] ---[ end trace d36d91c626ac81a5 ]---
>> [   98.185098] ------------[ cut here ]------------
>> [   98.190903] WARNING: at drivers/cpufreq/cpufreq_governor.c:172 gov_queue_work+0xf0/0x110()
>> [   98.200387] Modules linked in: ext2 vfat fat loop
>> [   98.205029] nouveau W[   PFIFO][0000:03:00.0] unknown intr 0x00400000, ch 1
>> [   98.214563]  usbhid snd_hda_codec_hdmi coretemp kvm_intel kvm snd_hda_codec_realtek snd_hda_intel snd_hda_codec ehci_pci xhci_hcd ehci_hcd usbcore crc32_pclmul crc32c_intel snd_hwdep snd_pcm snd_page_alloc snd_timer ghash_clmulni_intel snd aesni_intel aes_x86_64 glue_helper sb_edac edac_core acpi_cpufreq mperf pcspkr lrw gf128mul ablk_helper cryptd iTCO_wdt iTCO_vendor_support evdev soundcore lpc_ich mfd_core processor dcdbas i2c_i801 usb_common button microcode
>> [   98.258886] CPU: 0 PID: 318 Comm: kworker/7:1 Tainted: G        W    3.10.0-rc1+ #2
>> [   98.267919] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A08 01/24/2013
>> [   98.276689] Workqueue: events od_dbs_timer
>> [   98.282147]  0000000000000009 ffff88043969dc78 ffffffff8161445c ffff88043969dcb8
>> [   98.290991]  ffffffff8103e540 ffff88043b712a80 0000000000000007 ffff88043a295200
>> [   98.299832]  ffff88043b712a80 ffffffff81cdc910 0000000000000007 ffff88043969dcc8
>> [   98.308671] Call Trace:
>> [   98.312471]  [<ffffffff8161445c>] dump_stack+0x19/0x1b
>> [   98.318982]  [<ffffffff8103e540>] warn_slowpath_common+0x70/0xa0
>> [   98.326376]  [<ffffffff8103e58a>] warn_slowpath_null+0x1a/0x20
>> [   98.333577]  [<ffffffff814f6bf0>] gov_queue_work+0xf0/0x110
>> [   98.340482]  [<ffffffff814f60bb>] od_dbs_timer+0xcb/0x170
>> [   98.347160]  [<ffffffff8105e75d>] process_one_work+0x1fd/0x540
>> [   98.354232]  [<ffffffff8105e6f2>] ? process_one_work+0x192/0x540
>> [   98.361471]  [<ffffffff8105ef22>] worker_thread+0x122/0x380
>> [   98.368260]  [<ffffffff8105ee00>] ? rescuer_thread+0x320/0x320
>> [   98.375309]  [<ffffffff8106634a>] kthread+0xea/0xf0
>> [   98.381385]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   98.388951]  [<ffffffff81623d9c>] ret_from_fork+0x7c/0xb0
>> [   98.395546]  [<ffffffff81066260>] ? flush_kthread_worker+0x150/0x150
>> [   98.403097] ---[ end trace d36d91c626ac81a6 ]---
>> [   98.409180] Power down.
>> [   98.413109] acpi_power_off called
>>
> 

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Borislav Petkov]

On Tue, May 21, 2013 at 10:20:51AM +0800, Michael Wang wrote:
> This is not enough to prove that policy->cpus is wrong, the cpu could
> be online when get from policy->cpus, but offline when checked here,
> since hotplug is able to happen during the period.

Strictly speaking you're correct but I don't do any hotplug besides the
one-time thing which is part of halting the box.

> I don't get it...
> 
> get_online_cpus() is just stop hotplug happen after it was invoked, so
> unless policy->cpus is really wrong, otherwise all the cpu it masked
> won't go offline any more.

Yes, that's my impression too - at the point we do gov_queue_work,
policy->cpus already contains offline cpus.

> This protect nothing...before we go here, the cpu could already
> offline, nothing changed...

Yes, but I don't want to schedule work on an offlined cpu and that is
ensured here.

> If you really want to confirm the policy->cpus was wrong, the way
> should be apply the fix I suggested, than check online in here.

Sure, feel free to get a box, enable NO_HZ_FULL and do all the
experimentations you desire. I surely cannot be the only one who
triggers this.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2

[Michael Wang]

On 05/21/2013 03:21 PM, Borislav Petkov wrote:
> On Tue, May 21, 2013 at 10:20:51AM +0800, Michael Wang wrote:
>> This is not enough to prove that policy->cpus is wrong, the cpu could
>> be online when get from policy->cpus, but offline when checked here,
>> since hotplug is able to happen during the period.
> 
> Strictly speaking you're correct but I don't do any hotplug besides the
> one-time thing which is part of halting the box.

Well, they share the same cpu_down() I suppose...

> 
>> I don't get it...
>>
>> get_online_cpus() is just stop hotplug happen after it was invoked, so
>> unless policy->cpus is really wrong, otherwise all the cpu it masked
>> won't go offline any more.
> 
> Yes, that's my impression too - at the point we do gov_queue_work,
> policy->cpus already contains offline cpus.
> 
>> This protect nothing...before we go here, the cpu could already
>> offline, nothing changed...
> 
> Yes, but I don't want to schedule work on an offlined cpu and that is
> ensured here.

IMHO, the problem seems mostly like the wrong usage of policy->cpus,
it's providing the right info, but just at that time, we don't need
worry about work on offlined cpu if we don't allow cpu disappear.

Your approach could be good respect to performance, but if we could
prove that policy->cpus is correct firstly, than we could fix the
problem without any concern, don't we?

> 
>> If you really want to confirm the policy->cpus was wrong, the way
>> should be apply the fix I suggested, than check online in here.
> 
> Sure, feel free to get a box, enable NO_HZ_FULL and do all the
> experimentations you desire. I surely cannot be the only one who
> triggers this.

I'm fine if the problem get solved, that means your box doesn't show
WARN any more :)

Regards,
Michael Wang

>