Re: [PATCH 2/3] docs: sysctl/kernel: document ftrace entries

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 28 Apr 2020 12:41:33 -0600
Jonathan Corbet <corbet@lwn.net> wrote:

> On Thu, 23 Apr 2020 20:36:50 +0200
> Stephen Kitt <steve@sk2.org> wrote:
> 
> > Based on the ftrace documentation, the tp_printk boot parameter
> > documentation, and the implementation in kernel/trace/trace.c.
> > 
> > Signed-off-by: Stephen Kitt <steve@sk2.org>  
> 
> This one could benefit from an ack from Steve (CC'd).  Also one other

Thanks! I verified that the documentation is correct.

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve



> little nit below:
> 
> >  Documentation/admin-guide/sysctl/kernel.rst | 50 +++++++++++++++++++++
> >  1 file changed, 50 insertions(+)
> > 
> > diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> > index 82bfd5892663..d4bbdaf96ebc 100644
> > --- a/Documentation/admin-guide/sysctl/kernel.rst
> > +++ b/Documentation/admin-guide/sysctl/kernel.rst
> > @@ -265,6 +265,27 @@ domain names are in general different. For a detailed discussion
> >  see the ``hostname(1)`` man page.
> >  
> >  
> > +ftrace_dump_on_oops
> > +===================
> > +
> > +Determines whether ``ftrace_dump()`` should be called on an oops (or
> > +kernel panic). This will output the contents of the ftrace buffers to
> > +the console.  This is very useful for capturing traces that lead to
> > +crashes and outputing it to a serial console.
> > +
> > += ===================================================
> > +0 Disabled (default).
> > +1 Dump buffers of all CPUs.
> > +2 Dump the buffer of the CPU that triggered the oops.
> > += ===================================================
> > +
> > +
> > +ftrace_enabled, stack_tracer_enabled
> > +====================================
> > +
> > +See :doc:`/trace/ftrace`.
> > +
> > +
> >  hardlockup_all_cpu_backtrace
> >  ============================
> >  
> > @@ -1191,6 +1212,35 @@ If a value outside of this range is written to ``threads-max`` an
> >  ``EINVAL`` error occurs.
> >  
> >  
> > +traceoff_on_warning
> > +===================
> > +
> > +When set, disables tracing (see :doc:`/trace/ftrace`) when a
> > +``WARN()`` is hit.
> > +
> > +
> > +tracepoint_printk
> > +=================
> > +
> > +When tracepoints are sent to printk() (enabled by the ``tp_printk``
> > +boot parameter), this entry provides runtime control::
> > +
> > +    echo 0 > /proc/sys/kernel/tracepoint_printk
> > +
> > +will stop tracepoints from being sent to printk(), and
> > +
> > +::  
> 
> I would just make that ", and::" and avoid the separate line.
> 
> > +
> > +    echo 1 > /proc/sys/kernel/tracepoint_printk
> > +
> > +will send them to printk() again.
> > +
> > +This only works if the kernel was booted with ``tp_printk`` enabled.
> > +
> > +See :doc:`/admin-guide/kernel-parameters` and
> > +:doc:`/trace/boottime-trace`.
> > +
> > +
> >  unknown_nmi_panic
> >  =================
> >    
> 
> Thanks,
> 
> jon