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Subject[PATCH 4.19 052/321] tracing: Lock event_mutex before synth_event_mutex
Date
From: Masami Hiramatsu <mhiramat@kernel.org>

[ Upstream commit fc800a10be26017f8f338bc8e500d48e3e6429d9 ]

synthetic event is using synth_event_mutex for protecting
synth_event_list, and event_trigger_write() path acquires
locks as below order.

event_trigger_write(event_mutex)
->trigger_process_regex(trigger_cmd_mutex)
->event_hist_trigger_func(synth_event_mutex)

On the other hand, synthetic event creation and deletion paths
call trace_add_event_call() and trace_remove_event_call()
which acquires event_mutex. In that case, if we keep the
synth_event_mutex locked while registering/unregistering synthetic
events, its dependency will be inversed.

To avoid this issue, current synthetic event is using a 2 phase
process to create/delete events. For example, it searches existing
events under synth_event_mutex to check for event-name conflicts, and
unlocks synth_event_mutex, then registers a new event under event_mutex
locked. Finally, it locks synth_event_mutex and tries to add the
new event to the list. But it can introduce complexity and a chance
for name conflicts.

To solve this simpler, this introduces trace_add_event_call_nolock()
and trace_remove_event_call_nolock() which don't acquire
event_mutex inside. synthetic event can lock event_mutex before
synth_event_mutex to solve the lock dependency issue simpler.

Link: http://lkml.kernel.org/r/154140844377.17322.13781091165954002713.stgit@devbox

Reviewed-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/trace_events.h | 2 ++
kernel/trace/trace_events.c | 34 ++++++++++++++++++++++++++------
kernel/trace/trace_events_hist.c | 24 ++++++++++------------
3 files changed, 40 insertions(+), 20 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 78a010e19ed41..0643c083ed862 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -529,6 +529,8 @@ extern int trace_event_raw_init(struct trace_event_call *call);
extern int trace_define_field(struct trace_event_call *call, const char *type,
const char *name, int offset, int size,
int is_signed, int filter_type);
+extern int trace_add_event_call_nolock(struct trace_event_call *call);
+extern int trace_remove_event_call_nolock(struct trace_event_call *call);
extern int trace_add_event_call(struct trace_event_call *call);
extern int trace_remove_event_call(struct trace_event_call *call);
extern int trace_event_get_offsets(struct trace_event_call *call);
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 7345f5f8f3fe6..017f737237e60 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2302,11 +2302,11 @@ __trace_early_add_new_event(struct trace_event_call *call,
struct ftrace_module_file_ops;
static void __add_event_to_tracers(struct trace_event_call *call);

-/* Add an additional event_call dynamically */
-int trace_add_event_call(struct trace_event_call *call)
+int trace_add_event_call_nolock(struct trace_event_call *call)
{
int ret;
- mutex_lock(&event_mutex);
+ lockdep_assert_held(&event_mutex);
+
mutex_lock(&trace_types_lock);

ret = __register_event(call, NULL);
@@ -2314,6 +2314,16 @@ int trace_add_event_call(struct trace_event_call *call)
__add_event_to_tracers(call);

mutex_unlock(&trace_types_lock);
+ return ret;
+}
+
+/* Add an additional event_call dynamically */
+int trace_add_event_call(struct trace_event_call *call)
+{
+ int ret;
+
+ mutex_lock(&event_mutex);
+ ret = trace_add_event_call_nolock(call);
mutex_unlock(&event_mutex);
return ret;
}
@@ -2363,17 +2373,29 @@ static int probe_remove_event_call(struct trace_event_call *call)
return 0;
}

-/* Remove an event_call */
-int trace_remove_event_call(struct trace_event_call *call)
+/* no event_mutex version */
+int trace_remove_event_call_nolock(struct trace_event_call *call)
{
int ret;

- mutex_lock(&event_mutex);
+ lockdep_assert_held(&event_mutex);
+
mutex_lock(&trace_types_lock);
down_write(&trace_event_sem);
ret = probe_remove_event_call(call);
up_write(&trace_event_sem);
mutex_unlock(&trace_types_lock);
+
+ return ret;
+}
+
+/* Remove an event_call */
+int trace_remove_event_call(struct trace_event_call *call)
+{
+ int ret;
+
+ mutex_lock(&event_mutex);
+ ret = trace_remove_event_call_nolock(call);
mutex_unlock(&event_mutex);

return ret;
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index dac518977e7d0..11d952650fa72 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -914,7 +914,7 @@ static int register_synth_event(struct synth_event *event)
call->data = event;
call->tp = event->tp;

- ret = trace_add_event_call(call);
+ ret = trace_add_event_call_nolock(call);
if (ret) {
pr_warn("Failed to register synthetic event: %s\n",
trace_event_name(call));
@@ -938,7 +938,7 @@ static int unregister_synth_event(struct synth_event *event)
struct trace_event_call *call = &event->call;
int ret;

- ret = trace_remove_event_call(call);
+ ret = trace_remove_event_call_nolock(call);

return ret;
}
@@ -1015,12 +1015,10 @@ static void add_or_delete_synth_event(struct synth_event *event, int delete)
if (delete)
free_synth_event(event);
else {
- mutex_lock(&synth_event_mutex);
if (!find_synth_event(event->name))
list_add(&event->list, &synth_event_list);
else
free_synth_event(event);
- mutex_unlock(&synth_event_mutex);
}
}

@@ -1032,6 +1030,7 @@ static int create_synth_event(int argc, char **argv)
int i, consumed = 0, n_fields = 0, ret = 0;
char *name;

+ mutex_lock(&event_mutex);
mutex_lock(&synth_event_mutex);

/*
@@ -1104,8 +1103,6 @@ static int create_synth_event(int argc, char **argv)
goto err;
}
out:
- mutex_unlock(&synth_event_mutex);
-
if (event) {
if (delete_event) {
ret = unregister_synth_event(event);
@@ -1115,10 +1112,13 @@ static int create_synth_event(int argc, char **argv)
add_or_delete_synth_event(event, ret);
}
}
+ mutex_unlock(&synth_event_mutex);
+ mutex_unlock(&event_mutex);

return ret;
err:
mutex_unlock(&synth_event_mutex);
+ mutex_unlock(&event_mutex);

for (i = 0; i < n_fields; i++)
free_synth_field(fields[i]);
@@ -1129,12 +1129,10 @@ static int create_synth_event(int argc, char **argv)

static int release_all_synth_events(void)
{
- struct list_head release_events;
struct synth_event *event, *e;
int ret = 0;

- INIT_LIST_HEAD(&release_events);
-
+ mutex_lock(&event_mutex);
mutex_lock(&synth_event_mutex);

list_for_each_entry(event, &synth_event_list, list) {
@@ -1144,16 +1142,14 @@ static int release_all_synth_events(void)
}
}

- list_splice_init(&event->list, &release_events);
-
- mutex_unlock(&synth_event_mutex);
-
- list_for_each_entry_safe(event, e, &release_events, list) {
+ list_for_each_entry_safe(event, e, &synth_event_list, list) {
list_del(&event->list);

ret = unregister_synth_event(event);
add_or_delete_synth_event(event, !ret);
}
+ mutex_unlock(&synth_event_mutex);
+ mutex_unlock(&event_mutex);

return ret;
}
--
2.20.1


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