On 06/29, zhangwei(Jovi) wrote:
>
> [v3->v4]:
I am wondering how much you will hate me if I suggest to make v5 ;)
But look, imho probe_event_enable() looks a bit more confusing than
it needs.
> -probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
> +probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
> + filter_func_t filter)
> {
> + bool enabled = is_trace_uprobe_enabled(tu);
> + struct event_file_link *link;
> int ret = 0;
Unnecessary initialization.
> - if (is_trace_uprobe_enabled(tu))
> - return -EINTR;
> + if (file) {
> + if (tu->flags & TP_FLAG_PROFILE)
> + return -EINTR;
> +
> + link = kmalloc(sizeof(*link), GFP_KERNEL);
> + if (!link)
> + return -ENOMEM;
> +
> + link->file = file;
> + list_add_tail_rcu(&link->list, &tu->files);
> +
> + tu->flags |= TP_FLAG_TRACE;
> + } else {
> + if (tu->flags & TP_FLAG_TRACE)
> + return -EINTR;
> +
> + tu->flags |= TP_FLAG_PROFILE;
> + }
>
> WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>
> - tu->flags |= flag;
> - tu->consumer.filter = filter;
> - ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> - if (ret)
> - tu->flags &= ~flag;
> + /* we cannot call uprobe_register twice for same tu */
The comment is confusing, I'd suggest to simply remove it.
Yes, we can't do uprobe_register() twice as we already discussed.
But it is not that we "can't", we simply do not need this if uprobe
was already created.
> + if (!enabled) {
> + tu->consumer.filter = filter;
> + ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> + }
> +
> + if (ret) {
> + if (file) {
> + list_del_rcu(&link->list);
I won't insist, but _rcu is not needed in this case. Again, this looks
a bit confusing, as if we expect that some rcu reader can ever see this
entry. But this is not true and we are going to just kfree it without
synchronize_rcu().
> + kfree(link);
> + tu->flags &= ~TP_FLAG_TRACE;
> + } else
> + tu->flags &= ~TP_FLAG_PROFILE;
> + }
This is correct, but again, this is not immediately obvious.
Why it is correct to correct to clear TP_FLAG_TRACE? Because we know
that "enabled" was false and thus we remove the single list entry.
So, perhaps,
if (enabled)
return 0;
ret = uprobe_register();
if (ret) {
...;
}
return ret;
will be a bit more clean.
Oleg.
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