Commit 417944c4 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
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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: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 7818b388

include/linux/ftrace_event.h

+14 −6
Original line number Diff line number Diff line
@@ -251,16 +251,23 @@ struct ftrace_subsystem_dir; 
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 @@ struct ftrace_event_file { 
	 * 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)				\

include/trace/ftrace.h

+8 −0
Original line number Diff line number Diff line
@@ -413,6 +413,10 @@ static inline notrace int ftrace_get_offsets_##call( \ 
 *	int __data_size;

 *	int pc;

 *

 *	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT,

 *		     &ftrace_file->flags))

 *		return;

 *

 *	local_save_flags(irq_flags);

 *	pc = preempt_count();

 *
@@ -518,6 +522,10 @@ ftrace_raw_event_##call(void *__data, proto) \ 
	int __data_size;						\

	int pc;								\

									\

	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT,			\

		     &ftrace_file->flags))				\

		return;							\

									\

	local_save_flags(irq_flags);					\

	pc = preempt_count();						\

									\

kernel/trace/trace_events.c

+62 −13
Original line number Diff line number Diff line
@@ -205,37 +205,77 @@ void trace_event_enable_cmd_record(bool enable) 


		if (enable) {

			tracing_start_cmdline_record();

			file->flags |= FTRACE_EVENT_FL_RECORDED_CMD;

			set_bit(FTRACE_EVENT_FL_RECORDED_CMD_BIT, &file->flags);

		} else {

			tracing_stop_cmdline_record();

			file->flags &= ~FTRACE_EVENT_FL_RECORDED_CMD;

			clear_bit(FTRACE_EVENT_FL_RECORDED_CMD_BIT, &file->flags);

		}

	} while_for_each_event_file();

	mutex_unlock(&event_mutex);

}



static int ftrace_event_enable_disable(struct ftrace_event_file *file,

				       int enable)

static int __ftrace_event_enable_disable(struct ftrace_event_file *file,

					 int enable, int soft_disable)

{

	struct ftrace_event_call *call = file->event_call;

	int ret = 0;

	int disable;



	switch (enable) {

	case 0:

		if (file->flags & FTRACE_EVENT_FL_ENABLED) {

			file->flags &= ~FTRACE_EVENT_FL_ENABLED;

		/*

		 * When soft_disable is set and enable is cleared, we want

		 * to clear the SOFT_DISABLED flag but leave the event in the

		 * state that it was. That is, if the event was enabled and

		 * SOFT_DISABLED isn't set, then do nothing. But if SOFT_DISABLED

		 * is set we do not want the event to be enabled before we

		 * clear the bit.

		 *

		 * When soft_disable is not set but the SOFT_MODE flag is,

		 * we do nothing. Do not disable the tracepoint, otherwise

		 * "soft enable"s (clearing the SOFT_DISABLED bit) wont work.

		 */

		if (soft_disable) {

			disable = file->flags & FTRACE_EVENT_FL_SOFT_DISABLED;

			clear_bit(FTRACE_EVENT_FL_SOFT_MODE_BIT, &file->flags);

		} else

			disable = !(file->flags & FTRACE_EVENT_FL_SOFT_MODE);



		if (disable && (file->flags & FTRACE_EVENT_FL_ENABLED)) {

			clear_bit(FTRACE_EVENT_FL_ENABLED_BIT, &file->flags);

			if (file->flags & FTRACE_EVENT_FL_RECORDED_CMD) {

				tracing_stop_cmdline_record();

				file->flags &= ~FTRACE_EVENT_FL_RECORDED_CMD;

				clear_bit(FTRACE_EVENT_FL_RECORDED_CMD_BIT, &file->flags);

			}

			call->class->reg(call, TRACE_REG_UNREGISTER, file);

		}

		/* If in SOFT_MODE, just set the SOFT_DISABLE_BIT */

		if (file->flags & FTRACE_EVENT_FL_SOFT_MODE)

			set_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &file->flags);

		break;

	case 1:

		/*

		 * When soft_disable is set and enable is set, we want to

		 * register the tracepoint for the event, but leave the event

		 * as is. That means, if the event was already enabled, we do

		 * nothing (but set SOFT_MODE). If the event is disabled, we

		 * set SOFT_DISABLED before enabling the event tracepoint, so

		 * it still seems to be disabled.

		 */

		if (!soft_disable)

			clear_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &file->flags);

		else

			set_bit(FTRACE_EVENT_FL_SOFT_MODE_BIT, &file->flags);



		if (!(file->flags & FTRACE_EVENT_FL_ENABLED)) {



			/* Keep the event disabled, when going to SOFT_MODE. */

			if (soft_disable)

				set_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &file->flags);



			if (trace_flags & TRACE_ITER_RECORD_CMD) {

				tracing_start_cmdline_record();

				file->flags |= FTRACE_EVENT_FL_RECORDED_CMD;

				set_bit(FTRACE_EVENT_FL_RECORDED_CMD_BIT, &file->flags);

			}

			ret = call->class->reg(call, TRACE_REG_REGISTER, file);

			if (ret) {
@@ -244,7 +284,7 @@ static int ftrace_event_enable_disable(struct ftrace_event_file *file, 
					"%s\n", call->name);

				break;

			}

			file->flags |= FTRACE_EVENT_FL_ENABLED;

			set_bit(FTRACE_EVENT_FL_ENABLED_BIT, &file->flags);



			/* WAS_ENABLED gets set but never cleared. */

			call->flags |= TRACE_EVENT_FL_WAS_ENABLED;
@@ -255,6 +295,12 @@ static int ftrace_event_enable_disable(struct ftrace_event_file *file, 
	return ret;

}



static int ftrace_event_enable_disable(struct ftrace_event_file *file,

				       int enable)

{

	return __ftrace_event_enable_disable(file, enable, 0);

}



static void ftrace_clear_events(struct trace_array *tr)

{

	struct ftrace_event_file *file;
@@ -547,12 +593,15 @@ event_enable_read(struct file *filp, char __user *ubuf, size_t cnt, 
	struct ftrace_event_file *file = filp->private_data;

	char *buf;



	if (file->flags & FTRACE_EVENT_FL_ENABLED)

		buf = "1\n";

	if (file->flags & FTRACE_EVENT_FL_ENABLED) {

		if (file->flags & FTRACE_EVENT_FL_SOFT_DISABLED)

			buf = "0*\n";

		else

			buf = "1\n";

	} else

		buf = "0\n";



	return simple_read_from_buffer(ubuf, cnt, ppos, buf, 2);

	return simple_read_from_buffer(ubuf, cnt, ppos, buf, strlen(buf));

}



static ssize_t

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