linux-kernel - Re: [kvm-devel] [BUG] Oops with KVM-27

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Date:	Wed, 13 Jun 2007 11:59:25 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Luca Tettamanti <kronos.it@...il.com>
CC:	kvm-devel@...ts.sf.net, linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [BUG] Oops with KVM-27

Luca Tettamanti wrote:
> Il Mon, Jun 11, 2007 at 10:44:45AM +0300, Avi Kivity ha scritto: 
>   
>> Luca wrote:
>>     
>>>> I've managed to reproduce this on kvm-21 (it takes many boots for this
>>>> to happen, but it does eventually).
>>>>         
>>> Hum, any clue on the cause? 
>>>       
>> From what I've seen, it's the new Linux clocksource code.
>>
>>     
>>> Should I test older versions?
>>>       
>> They're unlikely to be better.  Instead, it would be best to see what 
>> the guest is doing.
>>     
>
> RCU is not working. Network initialization hangs because it happens to
> be the first RCU user.
> The guest is stuck waiting for RCU syncronization:
>
> [    4.992207]  [<c04321c5>] synchronize_rcu+0x4e/0x80
> [    4.994379]  [<c0431db5>] wakeme_after_rcu+0x0/0x8
> [    4.996521]  [<c0599ad1>] synchronize_net+0x64/0x8c
> [    4.998678]  [<c05d70e0>] inet_register_protosw+0xef/0x151
> [    5.000984]  [<c072d79e>] inet_init+0x1cd/0x498
>
> wait_for_completion() in synchronize_rcu() calls schedule() and the
> completion is never signaled (wakeme_after_rcu is never called).
> The completion AFAICS would be signaled via rcu_process_callbacks(),
> which is called in tasklet context.
> Scheduler and completion are working fine since they're used in other
> part of the kernel without problems.
>
> To recap:
>
> i686 F7 kernel: always works.
>
> i586 F7 kernel: sometime hangs due to RCU problems. When it does work
> it's because the LAPIC is disabled on boot:
>
> Using local APIC timer interrupts.
> calibrating APIC timer ...
> ... lapic delta = 25745109
> ... PM timer delta = 0
> ..... delta 25745109
> ..... mult: 1105912110
> ..... calibration result: 4119217
> ..... CPU clock speed is 8794.0417 MHz.
> ..... host bus clock speed is 4119.0217 MHz.
> ... verify APIC timer
> ... jiffies delta = 103
> APIC timer disabled due to verification failure.
>
> When it doesn't work LAPIC passes the test:
>
> [    1.304717] Using local APIC timer interrupts.
> [    1.304719] calibrating APIC timer ...
> [    1.718823] ... lapic delta = 25251444
> [    1.720582] ... PM timer delta = 0
> [    1.722219] ..... delta 25251444
> [    1.723827] ..... mult: 1084706136
> [    1.725470] ..... calibration result: 4040231
> [    1.727374] ..... CPU clock speed is 8625.0780 MHz.
> [    1.729396] ..... host bus clock speed is 4040.0231 MHz.
> [    1.731540] ... verify APIC timer
> [    2.158342] ... jiffies delta = 102
> [    2.160035] ... jiffies result ok
>
> i586 F7 kernel, with 'nolapic': always works.
>   

Can you check which .config option causes it (a special type of 
bisecting...)?

This looks likely based on your findings:

-CONFIG_X86_ALIGNMENT_16=y
+CONFIG_X86_GOOD_APIC=y
 CONFIG_X86_INTEL_USERCOPY=y
+CONFIG_X86_USE_PPRO_CHECKSUM=y
+CONFIG_X86_TSC=y

I expect it's not directly related to i586 vs i686.


-- 
error compiling committee.c: too many arguments to function

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