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Message-ID: <466FB1ED.3090905@qumranet.com>
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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