Re: PATCH? trace_remove_event_call() should fail if call is active

[Oleg Nesterov <oleg@redhat.com>]

Masami,

I am not sure I understand. And please do not forget I am not
familiar with this code ;)

In short: do you think that the patch I sent "can't help" or
"not enough" ?

If "not enough" then I fully agree.

On 07/03, Masami Hiramatsu wrote:
>
> (2013/07/03 7:23), Oleg Nesterov wrote:
> > On 07/02, Oleg Nesterov wrote:
> >>
> >> So please ignore modules ;)
> >
> > Or lets discuss the change above.
>
> No, I think this still doesn't ensure that we can remove dynamic
> event safely. Since the event is related to several files under
> events/ dir and buffer instances, someone can just stay open the
> files while the event is removed and read/write it.

So, for example, event_enable_write() can happily play with
ftrace_event_file after unregister_trace_probe/free_trace_probe.

Did you mean this?

Sure, but this is another problem? And we already discussed it a
bit, an application can keep the file we need to remove opened.

As for event_enable_write() in particular, we can probably mark
file/call as dead somewhere in trace_remove_event_call(). But
I simply do not understand this code enough, I do not know what
else we should do.

IOW. So far _I think_ we just need the additional changes in
trace_remove_event_call() if it succeeds (with the patch I sent)
to prevent the races like above, but I didn't even try to think
about this problem.

Or I missed your point completely?

Oleg.