Messages in this thread | | | Date | Thu, 31 Mar 2022 19:10:05 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] ftrace: remove check of list iterator against head past the loop body |
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On Fri, 1 Apr 2022 00:37:52 +0200 Jakob Koschel <jakobkoschel@gmail.com> wrote:
Hi Jakob,
The patch looks fine, I have some small nits though.
First, the subject should actually be:
Subject: [PATCH] tracing: Remove check of list iterator against head past the loop body
Changes that only deal specifically with the function probes are labeled as "ftrace:", but the more generic changes that touches files outside of ftrace.c and fgraph.c should be "tracing:". Also, Linus prefers to have the next part of the subject start with a capital letter: "Remove" instead of "remove".
> 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/ [1] > 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..096f5a83358d 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); > @@ -4704,7 +4706,7 @@ unregister_ftrace_function_probe_func(char *glob, struct trace_array *tr, > { > struct ftrace_ops_hash old_hash_ops; > struct ftrace_func_entry *entry; > - struct ftrace_func_probe *probe; > + struct ftrace_func_probe *probe = NULL, *iter;
Can you move this to the first declaration to keep the nice "upside-down x-mas tree" look.
> 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 e11e167b7809..fe3dc157e635 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -2281,7 +2281,7 @@ event_subsystem_dir(struct trace_array *tr, const char *name, > struct trace_event_file *file, struct dentry *parent) > { > struct trace_subsystem_dir *dir; > - struct event_subsystem *system; > + struct event_subsystem *system, *iter;
And move this above dir as well, for the same reason.
Thanks,
-- Steve
> struct dentry *entry; > > /* First see if we did not already create this dir */ > @@ -2295,13 +2295,13 @@ 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) > > base-commit: f82da161ea75dc4db21b2499e4b1facd36dab275
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