Re: frequent lockups in 3.18rc4

[Sasha Levin]

On 12/07/2014 02:43 PM, Paul E. McKenney wrote:
> On Sun, Dec 07, 2014 at 10:24:20AM -0800, Paul E. McKenney wrote:
>> On Sun, Dec 07, 2014 at 09:58:14AM -0500, Sasha Levin wrote:
>>> On 12/05/2014 01:15 PM, Linus Torvalds wrote:
>>>> On Fri, Dec 5, 2014 at 7:03 AM, Sasha Levin <sasha.levin@xxxxxxxxxx> wrote:
>>>>>
>>>>> Yes, it's going to a serial line, but it's only about 100 lines/second on
>>>>> average. I wouldn't expect it to cause anything to hang!
>>>>
>>>> A regular 16650 serial chip? Running at 115kbps, I assume? So that's
>>>> about 11kB/s.
>>>>
>>>> And the serial console is polling, since it can't sleep or depend on interrupts.
>>>>
>>>> At a average line length of what, 40 characters? At less than 300
>>>> lines/s, you'd be using up 100% of one CPU. And since the printouts
>>>> are serialized, that would be all other CPU's too..
>>>>
>>>> 100 lines/s _average_ means that I can easily see it be 300lines/s for a while.
>>>>
>>>> So yeah. The serial console is simply not designed to handle
>>>> continuous output. It's for the "occasional" stuff.
>>>>
>>>> The fact that your rcu lockups go away when you make the fault
>>>> injection be quiet makes me really suspect this is related.
>>>
>>> The lockups themselves "go away", but looking closer at the log
>>> without those extra prints, I'm seeing:
>>>
>>> [ 1458.700070] INFO: rcu_preempt detected stalls on CPUs/tasks:
>>> [ 1458.700133]  (detected by 19, t=30502 jiffies, g=12293, c=12292, q=0)
>>> [ 1458.702764] INFO: Stall ended before state dump start
>>>
>>> Quite often.
>>>
>>> Maybe the extra prints were just a catalyst?
>>
>> Is anything else being printed about the time that these message show
>> up?  Or is this the only output for the 40,000 jiffies preceding this
>> message?

There's actually nothing going on (beyond fuzzing noise) before/after:

[  756.618342] kexec-bzImage64: Not a bzImage
[  762.381734] kexec-bzImage64: Not a bzImage
[  765.129612] Unable to find swap-space signature
[  771.022304] Unable to find swap-space signature
[  793.434417] kexec-bzImage64: Not a bzImage
[  797.978210] => alloc_cpumask_var: failed!
[  800.253116] kexec-bzImage64: Not a bzImage
[  818.280056] INFO: rcu_sched detected stalls on CPUs/tasks:
[  818.280056]  (detected by 11, t=30503 jiffies, g=-295, c=-296, q=0)
[  818.283400] INFO: Stall ended before state dump start
[  829.523992] audit: type=1326 audit(39.680:47): auid=4294967295 uid=2385760256 gid=2214330370 ses=4294967295 pid=13307 comm="trinity-c353" exe="/trinity/trinity" sig=9 arch=c000003e syscall=96 compat=0 ip=0x7fffcb7bee47 code=0x0
[  830.890841] audit: type=1326 audit(41.010:48): auid=4294967295 uid=310902784 gid=201841673 ses=4294967295 pid=13294 comm="trinity-c350" exe="/trinity/trinity" sig=9 arch=c000003e syscall=96 compat=0 ip=0x7fffcb7bee47 code=0x0

> And could you please build with CONFIG_RCU_CPU_STALL_INFO=y and try
> this again?

I already have it set:

$ grep STALL_INFO .config
CONFIG_RCU_CPU_STALL_INFO=y


Thanks,
Sasha
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