Re: Kernel traces coming back with trash/clutter

[John Anthony Kazos Jr.]

> I am experimenting with the kernel (CentOSv4.4 x86_64, 2.6.9-42.0.10)
> and I have added a number of traces in some relatively sensitive code
> in the page cache and some i/o functions.
> 
> I am getting this odd content in the trace log (dmesg), and I cannot
> figure out what it is or why it is there.
> 
> 4296757675 pdflush(80): do_writepages: map>ops>wrtpgs ffffffffa0195ff5
> 4296757675 pdflush(80): mpage_writepages w/b index 49728 pages 256000
> <7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7>
> <7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7>
> <7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7>
> <7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7>
> <7><7><7><7><7>__bio_add_page: 2x ph 88>=128 || hw 88>=88 || 360448>max
> ffffffff802525d8 generic_make_request(bio 000001017c745300) 50729472, 704
> __make_request(q 00000101b9293870, bio 000001017c745300: sdc; 50729600, 704)
> ll_new_hw_segment: 70 + 29 > 88
> <7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7>
> <7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7>
> <7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7>
> <7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7><7>
> <7><7><7><7>__bio_add_page: 2x ph 88>=128 || hw 88>=88 || 360448>max
> ffffffff802525d8 generic_make_request(bio 000001017c745a80) 50730176, 704
> __make_request(q 00000101b9293870, bio 000001017c745a80: sdc; 50730304, 704)
> 4296757684 swapper(0): dl_mv2dsp: sdc start 50710368 secs 1408
> 
> (The lines with the <7>s in them are long - I wrapped them for ease of
> reading and to keep the width down somewhat.)
> 
> Any feedback that might illuminate this would be welcome.  Please CC
> me personally as I am not yet able to subscribe to this list
> (apologies).

"<7>" is KERN_DEBUG in <include/linux/kernel.h>, used with printk. Are you 
using printk in the following forms?

printk(KERN_DEBUG "A debug message.\n");

...or...

const char msg_debug[] = KERN_DEBUG "A debug message.\n";
printk(msg_debug);

Perhaps you have something looping that's outputting KERN_DEBUG with a 
null message? Or one of your diagnostic printk statements includes 
KERN_DEBUG with no actual message?

Remember, if you have a string in a variable without a KERN_* 
prependation, you can do this.

printk(KERN_DEBUG "%s\n", debug_message);
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