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authorSteven Rostedt <rostedt@goodmis.org>2014-05-28 13:14:40 -0400
committerSteven Rostedt <rostedt@goodmis.org>2014-05-29 20:13:59 -0400
commit2184db46e425c2b84a783eeead0e2b24ce67cd7f (patch)
tree729fe482333786cd109018786de122873d6e634d /kernel/trace/trace.c
parent607e3a29203633eaec7334f2f58f9653df788a06 (diff)
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 NOTICE NOTICE ** ** ** ** trace_printk() being used. Allocating extra memory. ** ** ** ** This means that this is a DEBUG kernel and it is ** ** unsafe for produciton use. ** ** ** ** If you see this message and you are not debugging ** ** the kernel, report this immediately to your vendor! ** ** ** ** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE ** ********************************************************** That should hopefully keep developers from trying to sneak in a trace_printk() or two. Link: http://lkml.kernel.org/p/20140528131440.2283213c@gandalf.local.home Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/trace.c')
-rw-r--r--kernel/trace/trace.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 05431696b10c..eb228b9de170 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1975,7 +1975,21 @@ void trace_printk_init_buffers(void)
if (alloc_percpu_trace_buffer())
return;
- pr_info("ftrace: Allocated trace_printk buffers\n");
+ /* trace_printk() is for debug use only. Don't use it in production. */
+
+ pr_warning("\n**********************************************************\n");
+ pr_warning("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
+ pr_warning("** **\n");
+ pr_warning("** trace_printk() being used. Allocating extra memory. **\n");
+ pr_warning("** **\n");
+ pr_warning("** This means that this is a DEBUG kernel and it is **\n");
+ pr_warning("** unsafe for produciton use. **\n");
+ pr_warning("** **\n");
+ pr_warning("** If you see this message and you are not debugging **\n");
+ pr_warning("** the kernel, report this immediately to your vendor! **\n");
+ pr_warning("** **\n");
+ pr_warning("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
+ pr_warning("**********************************************************\n");
/* Expand the buffers to set size */
tracing_update_buffers();