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Old 10-16-2018, 03:21 AM   #1
ekinakoglu
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"DEBUG kernel" notice from dmesg output on Slackware64 14.2 with kernel 4.4.157


I get the notice below from dmesg on Slackware64 14.2 with kernel 4.4.157:

Code:
[   76.971614] **********************************************************
[   76.971617] **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
[   76.971620] **                                                      **
[   76.971623] ** trace_printk() being used. Allocating extra memory.  **
[   76.971625] **                                                      **
[   76.971628] ** This means that this is a DEBUG kernel and it is     **
[   76.971631] ** unsafe for production use.                           **
[   76.971633] **                                                      **
[   76.971636] ** If you see this message and you are not debugging    **
[   76.971639] ** the kernel, report this immediately to your vendor!  **
[   76.971641] **                                                      **
[   76.971644] **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
[   76.971647] **********************************************************
Is there something wrong with the Slackware's latest kernel update? Should we inform Patrick or is this configuration on purpose?
 
Old 10-16-2018, 05:50 AM   #2
hazel
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Yes, I think you should report it if the kernel team don't think this option should be set in a production kernel.

It probably slipped through by accident. Patrick has a lot on his plate!
 
Old 10-16-2018, 08:09 AM   #3
phenixia2003
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Hello,

This notice has been introduced by this (old) commit :
Quote:
trace_printk() is used to debug fast paths within the kernel. Places that gets called in any context (interrupt or NMI) or thousands of times a second. Something you do not want to do with a printk(). In order to make it completely lockless as it needs a temporary buffer to handle some of the string formatting, a page is created per cpu for every context (four per cpu; normal, softirq, irq, NMI). Since trace_printk() should only be used for debugging purposes, there's no reason to waste memory on these buffers on a production system. That means, trace_printk() should never be used unless a developer is debugging their kernel. There's macro magic to allocate the buffers if trace_printk() is used anywhere in the kernel. To help enforce that trace_printk() isn't used outside of development, when it is used, a nasty banner is displayed on bootup (or when a module is loaded that uses trace_printk() and the kernel core does not).
I guess the OP encounters this only because of a module that uses trace_printk().

--
SeB
 
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Old 10-16-2018, 11:08 AM   #4
hazel
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Well, if it's an in-tree module, it shouldn't be using this function either. So I still think it should be reported.

There is another possibility: that the OP is using a proprietary kernel module which is badly written. There's not much that can be done about that. But I think he'd know if he was. Wouldn't the kernel report itself as tainted?
 
Old 10-16-2018, 12:35 PM   #5
volkerdi
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Quote:
Originally Posted by ekinakoglu View Post
I get the notice below from dmesg on Slackware64 14.2 with kernel 4.4.157:
I'm not normally seeing this in dmesg on x86_64 14.2 here, but what modules are you using?

You will get that message if you load the ring_buffer_benchmark module, since that makes use of trace_printk().
 
Old 10-17-2018, 01:31 AM   #6
ekinakoglu
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After Patrick's message, I reviewed the modules in use for my kernel.

I am using Intel Parallel Studio (Fortran and C compilers and other tools) and I know that it loads some modules. Inspecting the "dmesg" output in detail I discovered that the "notice" was displayed just after socperf2_0 module had been loaded by Intel VTune Amplifier of the Intel Parallel Studio. I uninstalled the product, restarted the machine and checked again, and the "notice" was gone.

Thank you all for your help.
 
  


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