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

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Message-ID: <20200428124133.0fbaf7c5@lwn.net>
Date:   Tue, 28 Apr 2020 12:41:33 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Stephen Kitt <steve@....org>
Cc:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/3] docs: sysctl/kernel: document ftrace entries

On Thu, 23 Apr 2020 20:36:50 +0200
Stephen Kitt <steve@....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@....org>

This one could benefit from an ack from Steve (CC'd).  Also one other
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