Messages in this thread Patch in this message | | | Date | Wed, 28 May 2014 13:14:40 -0400 | From | Steven Rostedt <> | Subject | [RFC][PATCH] tracing: Print nasty banner when trace_printk() is in use |
| |
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?
Not-yet-signed-off-by: Steven Rostedt <rostedt@goodmis.org> ---
Ted,
I noticed that in fs/ext4/inline.c you use trace_printk() if INLINE_DIR_DEBUG is defined. I'm assuming that this is not a production setting and this banner should not affect you at all. Am I correct?
There's some other places that use it, but those are obviously debug only.
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 0543169..068f453 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -1975,7 +1975,11 @@ void trace_printk_init_buffers(void) if (alloc_percpu_trace_buffer()) return; - pr_info("ftrace: Allocated trace_printk buffers\n"); + pr_warning("****************************************\n"); + pr_warning("** NOTICE NOTICE NOTICE NOTICE NOTICE **\n"); + pr_warning("** trace_printk() being used. **\n"); + pr_warning("** Allocating extra memory for it **\n"); + pr_warning("****************************************\n"); /* Expand the buffers to set size */ tracing_update_buffers();
| |