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Subject[PATCH 4/5] ftrace: Add task_comm support for trace_event
Date
From: Zhaolei <zhaolei@cn.fujitsu.com>

If we enable a trace event alone without any tracer running (such as
function tracer, sched switch tracer, etc...) it can't output enough
task command information.

We need to use the tracing_{start/stop}_cmdline_record() helpers
which are designed to keep track of cmdlines for any tasks that
were scheduled during the tracing.
Before this patch:
# echo 1 > debugfs/tracing/events/sched/sched_switch/enable
# cat debugfs/tracing/trace
# tracer: nop
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
<...>-2289 [000] 526276.724790: sched_switch: task bash:2289 [120] ==> sshd:2287 [120]
<...>-2287 [000] 526276.725231: sched_switch: task sshd:2287 [120] ==> bash:2289 [120]
<...>-2289 [000] 526276.725452: sched_switch: task bash:2289 [120] ==> sshd:2287 [120]
<...>-2287 [000] 526276.727181: sched_switch: task sshd:2287 [120] ==> swapper:0 [140]
<idle>-0 [000] 526277.032734: sched_switch: task swapper:0 [140] ==> events/0:5 [115]
<...>-5 [000] 526277.032782: sched_switch: task events/0:5 [115] ==> swapper:0 [140]
...
After this patch:
# tracer: nop
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
bash-2269 [000] 527347.989229: sched_switch: task bash:2269 [120] ==> sshd:2267 [120]
sshd-2267 [000] 527347.990960: sched_switch: task sshd:2267 [120] ==> bash:2269 [120]
bash-2269 [000] 527347.991143: sched_switch: task bash:2269 [120] ==> sshd:2267 [120]
sshd-2267 [000] 527347.992959: sched_switch: task sshd:2267 [120] ==> swapper:0 [140]
<idle>-0 [000] 527348.531989: sched_switch: task swapper:0 [140] ==> events/0:5 [115]
events/0-5 [000] 527348.532115: sched_switch: task events/0:5 [115] ==> swapper:0 [140]
...
Changelog:
v1->v2: Update Kconfig to select CONTEXT_SWITCH_TRACER in
ENABLE_EVENT_TRACING
v2->v3: v2 can solve problem that was caused by config EVENT_TRACING
alone, but when CONFIG_FTRACE is off and CONFIG_TRACING is
selected by other config, compile fail happened again.
This version solves it.

[ Impact: fix incomplete output of event tracing ]

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A14FDFE.2080402@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
kernel/trace/Kconfig | 9 +++++++--
kernel/trace/trace_events.c | 6 ++++++
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index f61be30..a508b9d 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -49,6 +49,11 @@ config FTRACE_NMI_ENTER
default y

config EVENT_TRACING
+ select CONTEXT_SWITCH_TRACER
+ bool
+
+config CONTEXT_SWITCH_TRACER
+ select MARKERS
bool

config TRACING
@@ -176,10 +181,10 @@ config SCHED_TRACER
This tracer tracks the latency of the highest priority task
to be scheduled in, starting from the point it has woken up.

-config CONTEXT_SWITCH_TRACER
+config ENABLE_CONTEXT_SWITCH_TRACER
bool "Trace process context switches"
select TRACING
- select MARKERS
+ select CONTEXT_SWITCH_TRACER
help
This tracer gets called from the context switch and records
all switching of tasks.
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 9e91c4a..9b246eb 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -85,6 +85,7 @@ static void ftrace_clear_events(void)

if (call->enabled) {
call->enabled = 0;
+ tracing_stop_cmdline_record();
call->unregfunc();
}
}
@@ -99,12 +100,14 @@ static void ftrace_event_enable_disable(struct ftrace_event_call *call,
case 0:
if (call->enabled) {
call->enabled = 0;
+ tracing_stop_cmdline_record();
call->unregfunc();
}
break;
case 1:
if (!call->enabled) {
call->enabled = 1;
+ tracing_start_cmdline_record();
call->regfunc();
}
break;
@@ -1058,6 +1061,7 @@ static void trace_module_remove_events(struct module *mod)
found = true;
if (call->enabled) {
call->enabled = 0;
+ tracing_stop_cmdline_record();
call->unregfunc();
}
if (call->event)
@@ -1262,11 +1266,13 @@ static __init void event_trace_self_tests(void)
}

call->enabled = 1;
+ tracing_start_cmdline_record();
call->regfunc();

event_test_stuff();

call->unregfunc();
+ tracing_stop_cmdline_record();
call->enabled = 0;

pr_cont("OK\n");
--
1.6.2.3


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