(2013/07/17 23:43), Oleg Nesterov wrote: > On 07/17, Masami Hiramatsu wrote: >> >> At a glance, you're trying to change which operation will be >> failed. Currently, user can not remove an event while someone >> opens files which related to the event. And this approach >> changes that the someone can remove the event even if the >> files are opened (and read/write operation will be failed). >> Am I understand correctly? > > Yes. > > Once again, I am still not sure and I am asking for your review.
OK, > But to me this looks much better. To simplify the discussion, lets > consider ftrace_enable_fops in particular. > > - Why should .open() block rmdir or unregister_uprobe_event? Because it is opened and under preparing for use. :) But, yeah, if we expect there is only one user using ftrace, accessing the removing event file is meaningless. It should be failed. > - Why do we need .open() at all? Whatever it can do to > validate file/call/etc, .read/write can do the same. Currently, just for preparing and reserving. > - If we kill .open/release, we do not need the nontrivial > refcounting. Everything becomes simple, no need to keep > the state "in between". That also means to refrain checking existence under locking mutex in all operations. And we have to check it, which I actually concern. refcounting is not so small and itself is complex, but it just needs to inc/dec on open/close. > We need event_mutex anyway (and note that other f_op's can > also rely on other locks taken by trace_remove_event_call), > the validation degrades to the trivial != NULL check. > > - This also simplifies trace_remove_event_call() paths, we > know that once it takes event_mutex nobody can play with > ftrace_event_file/ftrace_event_call we are going to free. Hmm, it seems that we can remove only refcount check, or more? Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
