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

Stephen Kitt
2020-04-29T23:24:40Z

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>
---
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