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tracing: Add tp_printk cmdline to have tracepoints go to printk()

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Add the kernel command line tp_printk option that will have tracepoints
that are active sent to printk() as well as to the trace buffer.

Passing "tp_printk" will activate this. To turn it off, the sysctl
/proc/sys/kernel/tracepoint_printk can have '0' echoed into it. Note,
this only works if the cmdline option is used. Echoing 1 into the sysctl
file without the cmdline option will have no affect.

Note, this is a dangerous option. Having high frequency tracepoints send
their data to printk() can possibly cause a live lock. This is another
reason why this is only active if the command line option is used.

Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1412121539300.16494@nanos

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Red Hat)
2014-12-12 22:27:10 -05:00
committed by Steven Rostedt
parent 5f893b2639
commit 0daa230296
6 changed files with 76 additions and 0 deletions
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include/linux/ftrace.h
+1
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@@ -879,6 +879,7 @@ static inline int test_tsk_trace_graph(struct task_struct *tsk)
enum ftrace_dump_mode;
extern enum ftrace_dump_mode ftrace_dump_on_oops;
extern int tracepoint_printk;
extern void disable_trace_on_warning(void);
extern int __disable_trace_on_warning;