是蟲啦，不是警告。在 Linux kernel 的 mailing list 看到一則有意思的張貼，全文如下，Jollen 把重點用紅色標示出來：

* Jeremy Fitzhardinge  wrote:

> A warning is a warning, not a BUG.

> - printk("BUG: warning at %s:%d/%s()n", __FILE__,
> + printk("WARNING at %s:%d %s()n", __FILE__,

i'm not really happy about this change.

Firstly, 
most WARN_ON()s are /bugs/, not warnings ... 
If it's a real
warning, a KERN_INFO printk should be done.

Secondly, the reason i changed it to the 'BUG: ...' format is that i
tried to make it easier for automated tools (and for users) to figure
out that a kernel bug happened.

Ingo
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很重要，一定要看的概念。在 Linux kernel 裡，WARN_ON() 所秀出來的訊息格式為「BUG: xxx」，表示這是一個臭蟲。如果是警告訊息，則是用 loglevel 'KERN_INFO' 來列印訊息。

所以，這位老兄解釋的很清楚，這類的 "warning" 訊息是 kernel 的 "bug"，並不是字面上所表示的「警告」訊息！