linux-kernel - [PATCH v2 1/2] docs: sysctl/kernel: document ftrace entries

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Message-Id: <20200429205757.8677-1-steve@sk2.org>
Date:   Wed, 29 Apr 2020 22:57:56 +0200
From:   Stephen Kitt <steve@....org>
To:     Jonathan Corbet <corbet@....net>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        linux-doc@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Stephen Kitt <steve@....org>
Subject: [PATCH v2 1/2] docs: sysctl/kernel: document ftrace entries

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>
---
Changes since v2:
  - spelling and grammar fixes in ftrace_dump_on_oops ("outputing it"
    -> "outputting them")
  - "and::" in a single line in tracepoint_printk

Documentation/admin-guide/sysctl/kernel.rst | 48 +++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 82bfd5892663..b1ad4c86274d 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 outputting them 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 +1212,33 @@ 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::
+
+    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
 =================
 
-- 
2.20.1