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SubjectRe: [RFC PATCH 0/4] tracing: fix open/delete fixes
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?


Once again, I am still not sure and I am asking for your review.

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?

- Why do we need .open() at all? Whatever it can do to
validate file/call/etc, .read/write can do the same.

- If we kill .open/release, we do not need the nontrivial
refcounting. Everything becomes simple, no need to keep
the state "in between".

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.


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