On 08/01, Steven Rostedt wrote: > > On Thu, 2013-08-01 at 15:34 +0200, Oleg Nesterov wrote: > > > > > > __unregister_trace_probe(tp); > > > list_del(&tp->list) > > > unregister_probe_event(tp) <-- fails! > > > free_trace_probe(tp) > > > > Yes. But again, this doesn't explain why unregister_probe_event()-> > > __trace_remove_event_call() can't simply proceed and > > do ftrace_event_enable_disable() + remove_event_from_tracers(). > > The problem is with the soft disable.
Exactly! This is another (also unlikely) race we need to prevent. > so the > i_private wont work. Yes, and this is another reason why trace_remove_event_call() can't always succeed, and the comment/changelog in probe_remove_event_call() (added by the previous change) even tries to document the problems with FL_SOFT_MODE. > > IOW, if we do not apply the previous "trace_remove_event_call() should > > fail if call/file is in use" patch, then everything is fine: > > > > > write(fd, "0", 1) > > > > this will fail with ENODEV. > > Currently it does not, because the failure in probe_remove_event_call() > due to the event being busy wont remove the event (event_remove() is > never called). Thus the event is still alive and the write will still > have access to it. Yes, yes. That is why the changelog says "Both trace_kprobe.c/trace_uprobe.c need the additional changes". IOW, the previous change itself adds the new races fixed by this patch (and the similar change in trace_uprobe.c). Hopefully this is fine because the code is buggy anyway. > I can update the change log to remove some of the functions that are > being called to be less confusing. I am fine either way. Just I wanted to be sure that we understand each other and I didn't miss something. > I agree, this isn't really nice, but for now we have to deal with it. Yes, yes, this is not for 3.11. Oleg. -- 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/