SMP kernels /w POLLING enabled - combination garbles(syncer?) console line message(s) on reboot

[Kris Kennaway]

Steven Hartland wrote:
> ----- Original Message ----- From: "Chargen" <chargen at gmail.com>
> To: <freebsd-current at freebsd.org>
> Sent: Saturday, January 26, 2008 4:36 AM
> Subject: 7cur: SMP kernels /w POLLING enabled - combination 
> garbles(syncer?) console line message(s) on reboot
> 
> 
>> 7cur: SMP kernels /w POLLING enabled - combination garbles (syncer?) 
>> console
>> line message(s) on reboot
>>
>> SMP kernel with POLLING enabled garbles one or more of the last lines in
>> console after issuing the {reboot} command
>>
>> options DEVICE_POLLING
>> options HZ=1000
>>
>> with or without sysctl -w kern.polling.enable=1 or sysctl -w
>> kern.polling.enable=0
>>
>> The garbled lines are between 'shutting down bufdaemon' and 'all buffs
>> synced'   (after 'bufdaemon', I presume these are the syncer, 'Syncing
>> disks, vnodes synced' lines)
>>
>> I found it only reproducable with SMP /apic enabled kernel. Console 
>> messages
>> after issuing reboot on UP kernels with polling_enabled  are readable.
>>
>> Note: polling wasn't manually set on any device (tested on UP and SMP
>> kernels) e.g.: no   ifconfig em0 polling
> 
> 
> Funny you should say that. Noticed that last night when rebooting one of
> our new 7.0 machines but assumed it was a one off remote console 
> corruption.
> 
> Just tested this again and its not. So I can confirm the corruption here
> on 7.0-PRERELEASE amd64 without polling.

It's harmless (actually a sign of increased concurrency); two threads 
are running printf concurrently.  Add options PRINTF_BUFR_SIZE=[...] if 
you don't want to see this.

Kris