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-rw-r--r--Documentation/trace/ftrace-uses.rst8
-rw-r--r--Documentation/trace/ftrace.rst4
2 files changed, 11 insertions, 1 deletions
diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst
index 1fbc69894eed..740bd0224d35 100644
--- a/Documentation/trace/ftrace-uses.rst
+++ b/Documentation/trace/ftrace-uses.rst
@@ -170,6 +170,14 @@ FTRACE_OPS_FL_RCU
a callback may be executed and RCU synchronization will not protect
it.
+FTRACE_OPS_FL_PERMANENT
+ If this is set on any ftrace ops, then the tracing cannot disabled by
+ writing 0 to the proc sysctl ftrace_enabled. Equally, a callback with
+ the flag set cannot be registered if ftrace_enabled is 0.
+
+ Livepatch uses it not to lose the function redirection, so the system
+ stays protected.
+
Filtering which functions to trace
==================================
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index e3060eedb22d..d2b5657ed33e 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -2976,7 +2976,9 @@ Note, the proc sysctl ftrace_enable is a big on/off switch for the
function tracer. By default it is enabled (when function tracing is
enabled in the kernel). If it is disabled, all function tracing is
disabled. This includes not only the function tracers for ftrace, but
-also for any other uses (perf, kprobes, stack tracing, profiling, etc).
+also for any other uses (perf, kprobes, stack tracing, profiling, etc). It
+cannot be disabled if there is a callback with FTRACE_OPS_FL_PERMANENT set
+registered.
Please disable this with care.