A while ago, the following innocuous printk was added to the p4-clockmod driver ..

printk(KERN_WARNING PFX “Unknown p4-clockmod-capable CPU. Please send an e-mail to <cpufreq at vger.kernel.org>\n”);

Which would get printed obviously, if it found a CPU on which it thought it might be able to work on, but would require checking by developers beforehand. Sounds like a great idea on the surface, but this one line turned out to be incredibly annoying.

The problem is that people run old kernels. (Be they self-built old kernels, irregularly updated distros, or even enterprise distros). So even though we removed that printk from the driver in October 2008, we still see the occasional report.

There was a similar situation with ACPI. It asked people to send dmidecode output to a mailing list, and people did so for many months after it stopped being interesting. The ACPI code still has 5 separate places where it asks users to send something to the mailing list, but it only does so in rare cases where we know there’s a BIOS bug. But it still has the effect that if they’re still there in n months time, they’ll live on in RHEL, SLES, Ubuntu LTS etc, even if upstream has stopped caring, or has worked around these bugs in some way.

A better solution to this situation would probably be to replace the ’send email’ messages with a ‘visit this website http:// ..’ printk. After it stops being interesting, the page could get updated to provide information such as “this is fixed in 2.6.40, you should ask your kernel vendor to remove the printk and apply this patch..”

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