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tracing: Add a way to soft disable trace events

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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>
This commit is contained in:
Steven Rostedt (Red Hat) 2013-03-12 13:26:18 -04:00 committed by Steven Rostedt
parent 7818b38865
commit 417944c4c7
3 changed files with 84 additions and 19 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

20
include/linux/ftrace_event.h
View file

@ -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) \

8
include/trace/ftrace.h
View file

@ -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(); \
\

75
kernel/trace/trace_events.c
View file

@ -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";
else
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