tracing: Add a way to soft disable trace events
In order to let triggers enable or disable events, we need a 'soft'
method for doing so. For example, if a function probe is added that
lets a user enable or disable events when a function is called, that
change must be done without taking locks or a mutex, and definitely
it can't sleep. But the full enabling of a tracepoint is expensive.
By adding a 'SOFT_DISABLE' flag, and converting the flags to be updated
without the protection of a mutex (using set/clear_bit()), this soft
disable flag can be used to allow critical sections to enable or disable
events from being traced (after the event has been placed into "SOFT_MODE").
Some caveats though: The comm recorder (to map pids with a comm) can not
be soft disabled (yet). If you disable an event with with a "soft"
disable and wait a while before reading the trace, the comm cache may be
replaced and you'll get a bunch of <...> for comms in the trace.
Reading the "enable" file for an event that is disabled will now give
you "0*" where the '*' denotes that the tracepoint is still active but
the event itself is "disabled".
[ fixed _BIT used in & operation : thanks to Dan Carpenter and smatch ]
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4cb6cd8..4e28b01 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -251,16 +251,23 @@
enum {
FTRACE_EVENT_FL_ENABLED_BIT,
FTRACE_EVENT_FL_RECORDED_CMD_BIT,
+ FTRACE_EVENT_FL_SOFT_MODE_BIT,
+ FTRACE_EVENT_FL_SOFT_DISABLED_BIT,
};
/*
* Ftrace event file flags:
* ENABLED - The event is enabled
* RECORDED_CMD - The comms should be recorded at sched_switch
+ * SOFT_MODE - The event is enabled/disabled by SOFT_DISABLED
+ * SOFT_DISABLED - When set, do not trace the event (even though its
+ * tracepoint may be enabled)
*/
enum {
FTRACE_EVENT_FL_ENABLED = (1 << FTRACE_EVENT_FL_ENABLED_BIT),
FTRACE_EVENT_FL_RECORDED_CMD = (1 << FTRACE_EVENT_FL_RECORDED_CMD_BIT),
+ FTRACE_EVENT_FL_SOFT_MODE = (1 << FTRACE_EVENT_FL_SOFT_MODE_BIT),
+ FTRACE_EVENT_FL_SOFT_DISABLED = (1 << FTRACE_EVENT_FL_SOFT_DISABLED_BIT),
};
struct ftrace_event_file {
@@ -274,17 +281,18 @@
* 32 bit flags:
* bit 0: enabled
* bit 1: enabled cmd record
+ * bit 2: enable/disable with the soft disable bit
+ * bit 3: soft disabled
*
- * Changes to flags must hold the event_mutex.
- *
- * Note: Reads of flags do not hold the event_mutex since
- * they occur in critical sections. But the way flags
+ * Note: The bits must be set atomically to prevent races
+ * from other writers. Reads of flags do not need to be in
+ * sync as they occur in critical sections. But the way flags
* is currently used, these changes do not affect the code
* except that when a change is made, it may have a slight
* delay in propagating the changes to other CPUs due to
- * caching and such.
+ * caching and such. Which is mostly OK ;-)
*/
- unsigned int flags;
+ unsigned long flags;
};
#define __TRACE_EVENT_FLAGS(name, value) \