On 2013/7/2 4:27, Oleg Nesterov wrote:
> On 06/29, zhangwei(Jovi) wrote:
>>
>> [v3->v4]:
>
> I am wondering how much you will hate me if I suggest to make v5 ;)
>
Feel free to do that :)
> 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().
>
Yes, _rcu is not needed in there.
>> + 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.
>
I will change it in v5 patch.
> Oleg.
>
>
> .
>
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