diff options
Diffstat (limited to 'Documentation/trace')
| -rw-r--r-- | Documentation/trace/ftrace-uses.rst | 10 | ||||
| -rw-r--r-- | Documentation/trace/ftrace.rst | 4 |
2 files changed, 12 insertions, 2 deletions
diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst index 1fbc69894eed..2a05e770618a 100644 --- a/Documentation/trace/ftrace-uses.rst +++ b/Documentation/trace/ftrace-uses.rst @@ -146,7 +146,7 @@ FTRACE_OPS_FL_RECURSION_SAFE itself or any nested functions that those functions call. If this flag is set, it is possible that the callback will also - be called with preemption enabled (when CONFIG_PREEMPT is set), + be called with preemption enabled (when CONFIG_PREEMPTION is set), but this is not guaranteed. FTRACE_OPS_FL_IPMODIFY @@ -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. |