* [PATCH v2 1/4] tracing: Remove usage of list iterator after the loop body
2022-04-27 17:07 [PATCH v2 0/4] Remove usage of list iterator after the loop body Jakob Koschel
@ 2022-04-27 17:07 ` Jakob Koschel
2022-04-27 17:07 ` [PATCH v2 2/4] tracing: Remove usage of list iterator variable after the loop Jakob Koschel
` (2 subsequent siblings)
3 siblings, 0 replies; 8+ messages in thread
From: Jakob Koschel @ 2022-04-27 17:07 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, linux-kernel, Jakob Koschel
In preparation to limit the scope of the list iterator variable to the
traversal loop, use a dedicated pointer to point to the found element
[1].
Before, the code implicitly used the head when no element was found
when using &pos->list. Since the new variable is only set if an
element was found, the head needs to be used explicitly if the
variable is NULL.
Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
---
kernel/trace/trace_output.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 8aa493d25c73..733a4d6c20e2 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -692,7 +692,7 @@ static LIST_HEAD(ftrace_event_list);
static int trace_search_list(struct list_head **list)
{
- struct trace_event *e;
+ struct trace_event *e = NULL, *iter;
int next = __TRACE_LAST_TYPE;
if (list_empty(&ftrace_event_list)) {
@@ -704,9 +704,11 @@ static int trace_search_list(struct list_head **list)
* We used up all possible max events,
* lets see if somebody freed one.
*/
- list_for_each_entry(e, &ftrace_event_list, list) {
- if (e->type != next)
+ list_for_each_entry(iter, &ftrace_event_list, list) {
+ if (iter->type != next) {
+ e = iter;
break;
+ }
next++;
}
@@ -714,7 +716,10 @@ static int trace_search_list(struct list_head **list)
if (next > TRACE_EVENT_TYPE_MAX)
return 0;
- *list = &e->list;
+ if (e)
+ *list = &e->list;
+ else
+ *list = &ftrace_event_list;
return next;
}
--
2.25.1
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v2 2/4] tracing: Remove usage of list iterator variable after the loop
2022-04-27 17:07 [PATCH v2 0/4] Remove usage of list iterator after the loop body Jakob Koschel
2022-04-27 17:07 ` [PATCH v2 1/4] tracing: " Jakob Koschel
@ 2022-04-27 17:07 ` Jakob Koschel
2022-04-27 17:07 ` [PATCH v2 3/4] tracing: Replace usage of found with dedicated list iterator variable Jakob Koschel
2022-04-27 17:07 ` [PATCH v2 4/4] tracing: Remove check of list iterator against head past the loop body Jakob Koschel
3 siblings, 0 replies; 8+ messages in thread
From: Jakob Koschel @ 2022-04-27 17:07 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, linux-kernel, Jakob Koschel
In preparation to limit the scope of a list iterator to the list
traversal loop, use a dedicated pointer to point to the found element
[1].
Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
---
kernel/trace/trace_events.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index e11e167b7809..e4a442060707 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1723,9 +1723,9 @@ static LIST_HEAD(event_subsystems);
static int subsystem_open(struct inode *inode, struct file *filp)
{
+ struct trace_subsystem_dir *dir = NULL, *iter_dir;
+ struct trace_array *tr = NULL, *iter_tr;
struct event_subsystem *system = NULL;
- struct trace_subsystem_dir *dir = NULL; /* Initialize for gcc */
- struct trace_array *tr;
int ret;
if (tracing_is_disabled())
@@ -1734,10 +1734,12 @@ static int subsystem_open(struct inode *inode, struct file *filp)
/* Make sure the system still exists */
mutex_lock(&event_mutex);
mutex_lock(&trace_types_lock);
- list_for_each_entry(tr, &ftrace_trace_arrays, list) {
- list_for_each_entry(dir, &tr->systems, list) {
- if (dir == inode->i_private) {
+ list_for_each_entry(iter_tr, &ftrace_trace_arrays, list) {
+ list_for_each_entry(iter_dir, &iter_tr->systems, list) {
+ if (iter_dir == inode->i_private) {
/* Don't open systems with no events */
+ tr = iter_tr;
+ dir = iter_dir;
if (dir->nr_events) {
__get_system_dir(dir);
system = dir->subsystem;
@@ -1753,9 +1755,6 @@ static int subsystem_open(struct inode *inode, struct file *filp)
if (!system)
return -ENODEV;
- /* Some versions of gcc think dir can be uninitialized here */
- WARN_ON(!dir);
-
/* Still need to increment the ref count of the system */
if (trace_array_get(tr) < 0) {
put_system(dir);
--
2.25.1
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v2 3/4] tracing: Replace usage of found with dedicated list iterator variable
2022-04-27 17:07 [PATCH v2 0/4] Remove usage of list iterator after the loop body Jakob Koschel
2022-04-27 17:07 ` [PATCH v2 1/4] tracing: " Jakob Koschel
2022-04-27 17:07 ` [PATCH v2 2/4] tracing: Remove usage of list iterator variable after the loop Jakob Koschel
@ 2022-04-27 17:07 ` Jakob Koschel
2022-04-27 17:07 ` [PATCH v2 4/4] tracing: Remove check of list iterator against head past the loop body Jakob Koschel
3 siblings, 0 replies; 8+ messages in thread
From: Jakob Koschel @ 2022-04-27 17:07 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, linux-kernel, Jakob Koschel
To move the list iterator variable into the list_for_each_entry_*()
macro in the future it should be avoided to use the list iterator
variable after the loop body.
To *never* use the list iterator variable after the loop it was
concluded to use a separate iterator variable instead of a
found boolean [1].
This removes the need to use a found variable and simply checking if
the variable was set, can determine if the break/goto was hit.
Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
---
kernel/trace/trace_events_hist.c | 15 +++++++--------
kernel/trace/trace_events_trigger.c | 24 +++++++++++-------------
2 files changed, 18 insertions(+), 21 deletions(-)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 44db5ba9cabb..65f79ac78742 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -6089,20 +6089,19 @@ static void hist_unregister_trigger(char *glob,
struct event_trigger_data *data,
struct trace_event_file *file)
{
+ struct event_trigger_data *test = NULL, *iter, *named_data = NULL;
struct hist_trigger_data *hist_data = data->private_data;
- struct event_trigger_data *test, *named_data = NULL;
- bool unregistered = false;
lockdep_assert_held(&event_mutex);
if (hist_data->attrs->name)
named_data = find_named_trigger(hist_data->attrs->name);
- list_for_each_entry(test, &file->triggers, list) {
- if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
- if (!hist_trigger_match(data, test, named_data, false))
+ list_for_each_entry(iter, &file->triggers, list) {
+ if (iter->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+ if (!hist_trigger_match(data, iter, named_data, false))
continue;
- unregistered = true;
+ test = iter;
list_del_rcu(&test->list);
trace_event_trigger_enable_disable(file, 0);
update_cond_flag(file);
@@ -6110,11 +6109,11 @@ static void hist_unregister_trigger(char *glob,
}
}
- if (unregistered && test->ops->free)
+ if (test && test->ops->free)
test->ops->free(test->ops, test);
if (hist_data->enable_timestamps) {
- if (!hist_data->remove || unregistered)
+ if (!hist_data->remove || test)
tracing_set_filter_buffering(file->tr, false);
}
}
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 7eb9d04f1c2e..349195c93da1 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -614,14 +614,13 @@ static void unregister_trigger(char *glob,
struct event_trigger_data *test,
struct trace_event_file *file)
{
- struct event_trigger_data *data;
- bool unregistered = false;
+ struct event_trigger_data *data = NULL, *iter;
lockdep_assert_held(&event_mutex);
- list_for_each_entry(data, &file->triggers, list) {
- if (data->cmd_ops->trigger_type == test->cmd_ops->trigger_type) {
- unregistered = true;
+ list_for_each_entry(iter, &file->triggers, list) {
+ if (iter->cmd_ops->trigger_type == test->cmd_ops->trigger_type) {
+ data = iter;
list_del_rcu(&data->list);
trace_event_trigger_enable_disable(file, 0);
update_cond_flag(file);
@@ -629,7 +628,7 @@ static void unregister_trigger(char *glob,
}
}
- if (unregistered && data->ops->free)
+ if (data && data->ops->free)
data->ops->free(data->ops, data);
}
@@ -1976,19 +1975,18 @@ void event_enable_unregister_trigger(char *glob,
struct trace_event_file *file)
{
struct enable_trigger_data *test_enable_data = test->private_data;
+ struct event_trigger_data *data = NULL, *iter;
struct enable_trigger_data *enable_data;
- struct event_trigger_data *data;
- bool unregistered = false;
lockdep_assert_held(&event_mutex);
- list_for_each_entry(data, &file->triggers, list) {
- enable_data = data->private_data;
+ list_for_each_entry(iter, &file->triggers, list) {
+ enable_data = iter->private_data;
if (enable_data &&
- (data->cmd_ops->trigger_type ==
+ (iter->cmd_ops->trigger_type ==
test->cmd_ops->trigger_type) &&
(enable_data->file == test_enable_data->file)) {
- unregistered = true;
+ data = iter;
list_del_rcu(&data->list);
trace_event_trigger_enable_disable(file, 0);
update_cond_flag(file);
@@ -1996,7 +1994,7 @@ void event_enable_unregister_trigger(char *glob,
}
}
- if (unregistered && data->ops->free)
+ if (data && data->ops->free)
data->ops->free(data->ops, data);
}
--
2.25.1
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v2 4/4] tracing: Remove check of list iterator against head past the loop body
2022-04-27 17:07 [PATCH v2 0/4] Remove usage of list iterator after the loop body Jakob Koschel
` (2 preceding siblings ...)
2022-04-27 17:07 ` [PATCH v2 3/4] tracing: Replace usage of found with dedicated list iterator variable Jakob Koschel
@ 2022-04-27 17:07 ` Jakob Koschel
3 siblings, 0 replies; 8+ messages in thread
From: Jakob Koschel @ 2022-04-27 17:07 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, linux-kernel, Jakob Koschel
When list_for_each_entry() completes the iteration over the whole list
without breaking the loop, the iterator value will be a bogus pointer
computed based on the head element.
While it is safe to use the pointer to determine if it was computed
based on the head element, either with list_entry_is_head() or
&pos->member == head, using the iterator variable after the loop should
be avoided.
In preparation to limit the scope of a list iterator to the list
traversal loop, use a dedicated pointer to point to the found element [1].
Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
---
kernel/trace/ftrace.c | 20 ++++++++++++--------
kernel/trace/trace_eprobe.c | 14 ++++++++------
kernel/trace/trace_events.c | 12 ++++++------
3 files changed, 26 insertions(+), 20 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4f1d2f5e7263..5c465e70d146 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4560,8 +4560,8 @@ register_ftrace_function_probe(char *glob, struct trace_array *tr,
struct ftrace_probe_ops *probe_ops,
void *data)
{
+ struct ftrace_func_probe *probe = NULL, *iter;
struct ftrace_func_entry *entry;
- struct ftrace_func_probe *probe;
struct ftrace_hash **orig_hash;
struct ftrace_hash *old_hash;
struct ftrace_hash *hash;
@@ -4580,11 +4580,13 @@ register_ftrace_function_probe(char *glob, struct trace_array *tr,
mutex_lock(&ftrace_lock);
/* Check if the probe_ops is already registered */
- list_for_each_entry(probe, &tr->func_probes, list) {
- if (probe->probe_ops == probe_ops)
+ list_for_each_entry(iter, &tr->func_probes, list) {
+ if (iter->probe_ops == probe_ops) {
+ probe = iter;
break;
+ }
}
- if (&probe->list == &tr->func_probes) {
+ if (!probe) {
probe = kzalloc(sizeof(*probe), GFP_KERNEL);
if (!probe) {
mutex_unlock(&ftrace_lock);
@@ -4702,9 +4704,9 @@ int
unregister_ftrace_function_probe_func(char *glob, struct trace_array *tr,
struct ftrace_probe_ops *probe_ops)
{
+ struct ftrace_func_probe *probe = NULL, *iter;
struct ftrace_ops_hash old_hash_ops;
struct ftrace_func_entry *entry;
- struct ftrace_func_probe *probe;
struct ftrace_glob func_g;
struct ftrace_hash **orig_hash;
struct ftrace_hash *old_hash;
@@ -4732,11 +4734,13 @@ unregister_ftrace_function_probe_func(char *glob, struct trace_array *tr,
mutex_lock(&ftrace_lock);
/* Check if the probe_ops is already registered */
- list_for_each_entry(probe, &tr->func_probes, list) {
- if (probe->probe_ops == probe_ops)
+ list_for_each_entry(iter, &tr->func_probes, list) {
+ if (iter->probe_ops == probe_ops) {
+ probe = iter;
break;
+ }
}
- if (&probe->list == &tr->func_probes)
+ if (!probe)
goto err_unlock_ftrace;
ret = -EINVAL;
diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index 541aa13581b9..63e901a28425 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -650,7 +650,7 @@ static struct trace_event_functions eprobe_funcs = {
static int disable_eprobe(struct trace_eprobe *ep,
struct trace_array *tr)
{
- struct event_trigger_data *trigger;
+ struct event_trigger_data *trigger = NULL, *iter;
struct trace_event_file *file;
struct eprobe_data *edata;
@@ -658,14 +658,16 @@ static int disable_eprobe(struct trace_eprobe *ep,
if (!file)
return -ENOENT;
- list_for_each_entry(trigger, &file->triggers, list) {
- if (!(trigger->flags & EVENT_TRIGGER_FL_PROBE))
+ list_for_each_entry(iter, &file->triggers, list) {
+ if (!(iter->flags & EVENT_TRIGGER_FL_PROBE))
continue;
- edata = trigger->private_data;
- if (edata->ep == ep)
+ edata = iter->private_data;
+ if (edata->ep == ep) {
+ trigger = iter;
break;
+ }
}
- if (list_entry_is_head(trigger, &file->triggers, list))
+ if (!trigger)
return -ENODEV;
list_del_rcu(&trigger->list);
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index e4a442060707..78f313b7b315 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2279,8 +2279,8 @@ static struct dentry *
event_subsystem_dir(struct trace_array *tr, const char *name,
struct trace_event_file *file, struct dentry *parent)
{
+ struct event_subsystem *system, *iter;
struct trace_subsystem_dir *dir;
- struct event_subsystem *system;
struct dentry *entry;
/* First see if we did not already create this dir */
@@ -2294,13 +2294,13 @@ event_subsystem_dir(struct trace_array *tr, const char *name,
}
/* Now see if the system itself exists. */
- list_for_each_entry(system, &event_subsystems, list) {
- if (strcmp(system->name, name) == 0)
+ system = NULL;
+ list_for_each_entry(iter, &event_subsystems, list) {
+ if (strcmp(iter->name, name) == 0) {
+ system = iter;
break;
+ }
}
- /* Reset system variable when not found */
- if (&system->list == &event_subsystems)
- system = NULL;
dir = kmalloc(sizeof(*dir), GFP_KERNEL);
if (!dir)
--
2.25.1
^ permalink raw reply related [flat|nested] 8+ messages in thread