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>
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@ -251,16 +251,23 @@ struct ftrace_subsystem_dir;
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enum {
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FTRACE_EVENT_FL_ENABLED_BIT,
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FTRACE_EVENT_FL_RECORDED_CMD_BIT,
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FTRACE_EVENT_FL_SOFT_MODE_BIT,
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FTRACE_EVENT_FL_SOFT_DISABLED_BIT,
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};
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/*
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* Ftrace event file flags:
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* ENABLED - The event is enabled
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* RECORDED_CMD - The comms should be recorded at sched_switch
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* SOFT_MODE - The event is enabled/disabled by SOFT_DISABLED
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* SOFT_DISABLED - When set, do not trace the event (even though its
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* tracepoint may be enabled)
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*/
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enum {
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FTRACE_EVENT_FL_ENABLED = (1 << FTRACE_EVENT_FL_ENABLED_BIT),
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FTRACE_EVENT_FL_RECORDED_CMD = (1 << FTRACE_EVENT_FL_RECORDED_CMD_BIT),
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FTRACE_EVENT_FL_SOFT_MODE = (1 << FTRACE_EVENT_FL_SOFT_MODE_BIT),
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FTRACE_EVENT_FL_SOFT_DISABLED = (1 << FTRACE_EVENT_FL_SOFT_DISABLED_BIT),
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};
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struct ftrace_event_file {
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@ -274,17 +281,18 @@ struct ftrace_event_file {
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* 32 bit flags:
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* bit 0: enabled
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* bit 1: enabled cmd record
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* bit 2: enable/disable with the soft disable bit
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* bit 3: soft disabled
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*
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* Changes to flags must hold the event_mutex.
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*
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* Note: Reads of flags do not hold the event_mutex since
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* they occur in critical sections. But the way flags
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* Note: The bits must be set atomically to prevent races
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* from other writers. Reads of flags do not need to be in
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* sync as they occur in critical sections. But the way flags
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* is currently used, these changes do not affect the code
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* except that when a change is made, it may have a slight
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* delay in propagating the changes to other CPUs due to
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* caching and such.
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* caching and such. Which is mostly OK ;-)
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*/
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unsigned int flags;
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unsigned long flags;
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};
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#define __TRACE_EVENT_FLAGS(name, value) \
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@ -413,6 +413,10 @@ static inline notrace int ftrace_get_offsets_##call( \
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* int __data_size;
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* int pc;
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*
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* if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT,
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* &ftrace_file->flags))
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* return;
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*
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* local_save_flags(irq_flags);
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* pc = preempt_count();
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*
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@ -518,6 +522,10 @@ ftrace_raw_event_##call(void *__data, proto) \
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int __data_size; \
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int pc; \
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\
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if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, \
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&ftrace_file->flags)) \
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return; \
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\
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local_save_flags(irq_flags); \
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pc = preempt_count(); \
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\
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@ -205,37 +205,77 @@ void trace_event_enable_cmd_record(bool enable)
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if (enable) {
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tracing_start_cmdline_record();
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file->flags |= FTRACE_EVENT_FL_RECORDED_CMD;
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set_bit(FTRACE_EVENT_FL_RECORDED_CMD_BIT, &file->flags);
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} else {
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tracing_stop_cmdline_record();
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file->flags &= ~FTRACE_EVENT_FL_RECORDED_CMD;
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clear_bit(FTRACE_EVENT_FL_RECORDED_CMD_BIT, &file->flags);
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}
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} while_for_each_event_file();
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mutex_unlock(&event_mutex);
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}
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static int ftrace_event_enable_disable(struct ftrace_event_file *file,
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int enable)
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static int __ftrace_event_enable_disable(struct ftrace_event_file *file,
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int enable, int soft_disable)
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{
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struct ftrace_event_call *call = file->event_call;
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int ret = 0;
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int disable;
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switch (enable) {
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case 0:
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if (file->flags & FTRACE_EVENT_FL_ENABLED) {
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file->flags &= ~FTRACE_EVENT_FL_ENABLED;
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/*
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* When soft_disable is set and enable is cleared, we want
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* to clear the SOFT_DISABLED flag but leave the event in the
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* state that it was. That is, if the event was enabled and
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* SOFT_DISABLED isn't set, then do nothing. But if SOFT_DISABLED
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* is set we do not want the event to be enabled before we
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* clear the bit.
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*
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* When soft_disable is not set but the SOFT_MODE flag is,
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* we do nothing. Do not disable the tracepoint, otherwise
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* "soft enable"s (clearing the SOFT_DISABLED bit) wont work.
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*/
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if (soft_disable) {
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disable = file->flags & FTRACE_EVENT_FL_SOFT_DISABLED;
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clear_bit(FTRACE_EVENT_FL_SOFT_MODE_BIT, &file->flags);
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} else
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disable = !(file->flags & FTRACE_EVENT_FL_SOFT_MODE);
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if (disable && (file->flags & FTRACE_EVENT_FL_ENABLED)) {
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clear_bit(FTRACE_EVENT_FL_ENABLED_BIT, &file->flags);
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if (file->flags & FTRACE_EVENT_FL_RECORDED_CMD) {
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tracing_stop_cmdline_record();
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file->flags &= ~FTRACE_EVENT_FL_RECORDED_CMD;
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clear_bit(FTRACE_EVENT_FL_RECORDED_CMD_BIT, &file->flags);
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}
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call->class->reg(call, TRACE_REG_UNREGISTER, file);
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}
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/* If in SOFT_MODE, just set the SOFT_DISABLE_BIT */
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if (file->flags & FTRACE_EVENT_FL_SOFT_MODE)
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set_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &file->flags);
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break;
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case 1:
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/*
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* When soft_disable is set and enable is set, we want to
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* register the tracepoint for the event, but leave the event
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* as is. That means, if the event was already enabled, we do
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* nothing (but set SOFT_MODE). If the event is disabled, we
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* set SOFT_DISABLED before enabling the event tracepoint, so
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* it still seems to be disabled.
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*/
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if (!soft_disable)
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clear_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &file->flags);
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else
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set_bit(FTRACE_EVENT_FL_SOFT_MODE_BIT, &file->flags);
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if (!(file->flags & FTRACE_EVENT_FL_ENABLED)) {
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/* Keep the event disabled, when going to SOFT_MODE. */
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if (soft_disable)
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set_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &file->flags);
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if (trace_flags & TRACE_ITER_RECORD_CMD) {
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tracing_start_cmdline_record();
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file->flags |= FTRACE_EVENT_FL_RECORDED_CMD;
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set_bit(FTRACE_EVENT_FL_RECORDED_CMD_BIT, &file->flags);
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}
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ret = call->class->reg(call, TRACE_REG_REGISTER, file);
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if (ret) {
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@ -244,7 +284,7 @@ static int ftrace_event_enable_disable(struct ftrace_event_file *file,
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"%s\n", call->name);
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break;
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}
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file->flags |= FTRACE_EVENT_FL_ENABLED;
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set_bit(FTRACE_EVENT_FL_ENABLED_BIT, &file->flags);
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/* WAS_ENABLED gets set but never cleared. */
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call->flags |= TRACE_EVENT_FL_WAS_ENABLED;
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@ -255,6 +295,12 @@ static int ftrace_event_enable_disable(struct ftrace_event_file *file,
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return ret;
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}
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static int ftrace_event_enable_disable(struct ftrace_event_file *file,
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int enable)
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{
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return __ftrace_event_enable_disable(file, enable, 0);
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}
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static void ftrace_clear_events(struct trace_array *tr)
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{
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struct ftrace_event_file *file;
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@ -547,12 +593,15 @@ event_enable_read(struct file *filp, char __user *ubuf, size_t cnt,
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struct ftrace_event_file *file = filp->private_data;
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char *buf;
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if (file->flags & FTRACE_EVENT_FL_ENABLED)
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buf = "1\n";
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else
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if (file->flags & FTRACE_EVENT_FL_ENABLED) {
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if (file->flags & FTRACE_EVENT_FL_SOFT_DISABLED)
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buf = "0*\n";
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else
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buf = "1\n";
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} else
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buf = "0\n";
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return simple_read_from_buffer(ubuf, cnt, ppos, buf, 2);
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return simple_read_from_buffer(ubuf, cnt, ppos, buf, strlen(buf));
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}
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static ssize_t
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