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

From: Avi Kivity
Date: Wed Jun 13 2007 - 04:59:37 EST

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:


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

error compiling committee.c: too many arguments to function

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