On Wed, May 28, 2014 at 01:14:40PM -0400, Steven Rostedt wrote: > > 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). > > Here's the banner: > > **************************************** > ** NOTICE NOTICE NOTICE NOTICE NOTICE ** > ** trace_printk() being used. ** > ** Allocating extra memory for it ** > **************************************** > > Hmm, maybe I should add "Not for production use" to scare people even > more?
Does that really stop people from doing stupid? Wouldn't it be better to make sure nobody merges a trace_printk() user in mainline? You can set up a commit hook and check for +.*trace_printk or so.
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