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SubjectRe: [RFC PATCH 2/2] tracing: Add tracepoint_printk cmdline
On Sat, 13 Dec 2014 11:59:25 +0100
Borislav Petkov <bp@alien8.de> wrote:

> On Sat, Dec 13, 2014 at 12:50:37AM -0500, Steven Rostedt wrote:
> >
> > Add the kernel command line tracepoint_printk option that will
> > have tracepoints that are active sent to printk().
> >
> > Passing "tracepoint_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.
> >
> > Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1412121539300.16494@nanos
> >
> > Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> > ---
> > Documentation/kernel-parameters.txt | 18 ++++++++++++++++++
> > include/linux/ftrace.h | 1 +
> > kernel/sysctl.c | 7 +++++++
> > kernel/trace/trace.c | 17 +++++++++++++++++
> > kernel/trace/trace.h | 1 +
> > kernel/trace/trace_events.c | 32 ++++++++++++++++++++++++++++++++
> > 6 files changed, 76 insertions(+)
> >
> > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> > index 1d09eb37c562..d81f464a7358 100644
> > --- a/Documentation/kernel-parameters.txt
> > +++ b/Documentation/kernel-parameters.txt
> > @@ -3500,6 +3500,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> > See also Documentation/trace/ftrace.txt "trace options"
> > section.
> >
> > + tracepoint_printk[FTRACE]
>
> Damn, this is long and most likely nasty to type on some dingy box when
> you're trying to debug stuff. Can we shorten it?
>
> trace_printk

No this is already taken.

> tp_printk

Actually, I was thinking about shortening it to tp_printk.

> tp_print
> tp_pr
> ...
>
> Last one is my favourite - we should call it ToiletPaper_Print :-)

What you need when your kernel is in the crapper.

-- Steve

>
> > + Have the tracepoints sent to printk as well as the
> > + tracing ring buffer. This is useful for early boot up
> > + where the system hangs or reboots and does not give the
> > + option for reading the tracing buffer or performing a
> > + ftrace_dump_on_oops.
>



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