[PATCH 10/32] tracing: Add NO_DISCARD event file flag

Tom Zanussi
2017-06-26T22:56:14Z

Whenever an event_command has a post-trigger that needs access to the
event record, the event record can't be discarded, or the post-trigger
will eventually see bogus data.

In order to allow the discard check to treat this case separately, add
an EVENT_FILE_FL_NO_DISCARD flag to the event file flags, along with
code in the discard check that checks the flag and avoids the discard
when the flag is set.

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
---
include/linux/trace_events.h | 3 +++
kernel/trace/trace.h | 13 ++++++++++---
kernel/trace/trace_events_trigger.c | 16 +++++++++++++---
3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index f333114..d7b230b 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -297,6 +297,7 @@ enum {
EVENT_FILE_FL_TRIGGER_MODE_BIT,
EVENT_FILE_FL_TRIGGER_COND_BIT,
EVENT_FILE_FL_PID_FILTER_BIT,
+ EVENT_FILE_FL_NO_DISCARD_BIT,
};

/*
@@ -311,6 +312,7 @@ enum {
* TRIGGER_MODE - When set, invoke the triggers associated with the event
* TRIGGER_COND - When set, one or more triggers has an associated filter
* PID_FILTER - When set, the event is filtered based on pid
+ * NO_DISCARD - When set, do not discard events, something needs them later
*/
enum {
EVENT_FILE_FL_ENABLED = (1 << EVENT_FILE_FL_ENABLED_BIT),
@@ -322,6 +324,7 @@ enum {
EVENT_FILE_FL_TRIGGER_MODE = (1 << EVENT_FILE_FL_TRIGGER_MODE_BIT),
EVENT_FILE_FL_TRIGGER_COND = (1 << EVENT_FILE_FL_TRIGGER_COND_BIT),
EVENT_FILE_FL_PID_FILTER = (1 << EVENT_FILE_FL_PID_FILTER_BIT),
+ EVENT_FILE_FL_NO_DISCARD = (1 << EVENT_FILE_FL_NO_DISCARD_BIT),
};

struct trace_event_file {
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 78c7694..81b1d07 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1271,9 +1271,16 @@ static inline void trace_buffer_unlock_commit(struct trace_array *tr,
if (eflags & EVENT_FILE_FL_TRIGGER_COND)
*tt = event_triggers_call(file, entry, event);

- if (test_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags) ||
- (unlikely(file->flags & EVENT_FILE_FL_FILTERED) &&
- !filter_match_preds(file->filter, entry))) {
+ if (unlikely(file->flags & EVENT_FILE_FL_FILTERED) &&
+ !filter_match_preds(file->filter, entry)) {
+ __trace_event_discard_commit(buffer, event);
+ return true;
+ }
+
+ if (test_bit(EVENT_FILE_FL_NO_DISCARD_BIT, &file->flags))
+ return false;
+
+ if (test_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags)) {
__trace_event_discard_commit(buffer, event);
return true;
}
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 9b0fe31..d345820 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -505,20 +505,30 @@ int trace_event_trigger_enable_disable(struct trace_event_file *file,
void update_cond_flag(struct trace_event_file *file)
{
struct event_trigger_data *data;
- bool set_cond = false;
+ bool set_cond = false, set_no_discard = false;

list_for_each_entry_rcu(data, &file->triggers, list) {
if (data->filter || event_command_post_trigger(data->cmd_ops) ||
- event_command_needs_rec(data->cmd_ops)) {
+ event_command_needs_rec(data->cmd_ops))
set_cond = true;
+
+ if (event_command_post_trigger(data->cmd_ops) &&
+ event_command_needs_rec(data->cmd_ops))
+ set_no_discard = true;
+
+ if (set_cond && set_no_discard)
break;
- }
}

if (set_cond)
set_bit(EVENT_FILE_FL_TRIGGER_COND_BIT, &file->flags);
else
clear_bit(EVENT_FILE_FL_TRIGGER_COND_BIT, &file->flags);
+
+ if (set_no_discard)
+ set_bit(EVENT_FILE_FL_NO_DISCARD_BIT, &file->flags);
+ else
+ clear_bit(EVENT_FILE_FL_NO_DISCARD_BIT, &file->flags);
}

/**
--
1.9.3