Printing from kernel

[Roman Kurakin]

Don Lewis wrote:

>On  7 Oct, Roman Kurakin wrote:
>  
>
>>Hi,
>>
>>	I have some problems with printing from kernel.
>>At first I think that my problems was cause I use printf,
>>but changed all of them to log cause it safe to use from
>>interrupt handlers. The situation become better but I still
>>observe system lockup in case I output some debug information
>>from my driver.
>>
>>	Also I have some problems with system console via com
>>port. Instead of messages from kernel I see the first letter
>>of the month name.
>>    
>>
>
>This is a bug in syslogd related to non-blocking I/O that bde and I
>discussed quite a while back, though we never figured out a proper fix.
>I recently made the interesting discovery that the same problem isn't
>present on sparc64.
>
>I think it'll start working again if you restart syslogd.
>  
>
 From my observation I didn't came to conclusion that this could be due 
to syslog,
but I'll check this.

>>	Could anybody comment my observation? Does anybody
>>saw anything like this?
>>
>>	Oh, I forget to say I observe that with both Current
>>and Releng5, SMP. Also I can't trigger NMI so I can't see the
>>point of lockup.
>>    
>>
>
>I generally use printf for this sort of thing, and I was going to
>suggest that you take a look at the KTR stuff, but that won't help if
>the machine totally locks up so that you can't get to the KTR buffer.
>
>I think you'll have trouble getting close to the bug if you use log
>because of the log latency from the generation of the message, passing
>it through syslogd, and back to the kernel to be printed.
>  
>
I'll try to think up how to see where I have my problems. If you plan to 
work on this problems
we could join our efforts,

rik

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>  
>