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SubjectRe: [PATCH 1/3] [BUGFIX] tracing: Fix double free of event_trigger_data
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Hi Steve,

On 7/24/2018 4:30 PM, Steven Rostedt wrote:
> On Tue, 24 Jul 2018 16:49:59 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
>>> Hmm it seems we should review the register_trigger() implementation.
>>> It should return the return value of trace_event_trigger_enable_disable(),
>>> shouldn't it?
>>>
>>
>> Yeah, that's not done well. I'll fix it up.
>>
>> Thanks for pointing it out.
>
> Tom,
>
> register_trigger() is messed up. I should have caught this when it was
> first submitted, but I'm totally confused. The comments don't match the
> code.
>
> First we have this:
>
> ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
> /*
> * The above returns on success the # of functions enabled,
> * but if it didn't find any functions it returns zero.
> * Consider no functions a failure too.
> */
>
> Which looks to be total BS.

Yes, it is BS in the case of event triggers. This was taken from the
ftrace function trigger code, where it does make sense. I think I left
it in thinking the code would at some point later converge.

>
> As we have this:
>
> /**
> * register_trigger - Generic event_command @reg implementation
> * @glob: The raw string used to register the trigger
> * @ops: The trigger ops associated with the trigger
> * @data: Trigger-specific data to associate with the trigger
> * @file: The trace_event_file associated with the event
> *
> * Common implementation for event trigger registration.
> *
> * Usually used directly as the @reg method in event command
> * implementations.
> *
> * Return: 0 on success, errno otherwise

And this is how it should work.

> */
> static int register_trigger(char *glob, struct event_trigger_ops *ops,
> struct event_trigger_data *data,
> struct trace_event_file *file)
> {
> struct event_trigger_data *test;
> int ret = 0;
>
> list_for_each_entry_rcu(test, &file->triggers, list) {
> if (test->cmd_ops->trigger_type == data->cmd_ops->trigger_type) {
> ret = -EEXIST;
> goto out;
> }
> }
>
> if (data->ops->init) {
> ret = data->ops->init(data->ops, data);
> if (ret < 0)
> goto out;
> }
>
> list_add_rcu(&data->list, &file->triggers);
> ret++;
>
> update_cond_flag(file);
> if (trace_event_trigger_enable_disable(file, 1) < 0) {
> list_del_rcu(&data->list);
> update_cond_flag(file);
> ret--;
> }
> out:
> return ret;
> }
>
> Where the comment is total wrong. It doesn't return 0 on success, it
> returns 1. And if trace_event_trigger_enable_disable() fails it returns
> zero.
>
> And that can fail with the call->class->reg() return value, which could
> fail for various strange reasons. I don't know why we would want to
> return 0 when it fails?
>
> I don't see where ->reg() would return anything but 1 on success. Maybe
> I'm missing something. I'll look some more, but I'm thinking of changing
> ->reg() to return zero on all success, and negative on all errors and
> just check those results.
>

Right, in the case of event triggers, we only register one at a time,
whereas with the trace function triggers, with globbing multiple
functions can register triggers at the same time, so it makes sense
there to have reg() return a count and the more convoluted error handling.

So I agree, simplifying things here by using the standard error handling
would be an improvement.

Tom

> -- Steve
>

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