tracing: Remove check of list iterator against head past the loop body

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://lkml.kernel.org/r/20220427170734.819891-5-jakobkoschel@gmail.com
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4f1d2f5..5c465e7 100644 (file)
--- 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 b045fa9..7d44785 100644 (file)
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -648,7 +648,7 @@ 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;
 
@@ -656,14 +656,16 @@ 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 e4a4420..78f313b 100644 (file)
--- 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)