On 07/31, Steven Rostedt wrote: > > On Wed, 2013-07-03 at 23:33 -0400, Steven Rostedt wrote: > > The above will corrupt the kprobe system, as the write to the enable > > file will happen after the kprobe was deleted. > > Oleg, > > The above no longer triggers the bug due to your changes. The race is > much tighter now
Yes, the changelog should be updated... > and requires a process with the enable file opened and > races with a write to enable it where the removal of the trace file > checks the trace disabled, sees that it is, continues, but then the > write enables it just as it gets deleted. This should be fine. Either event_remove() path takes event_mutex first and then ->write() fails, or ftrace_event_enable_disable() actually disables this even successfully. > Do you know of a way to trigger this bug? I'll try to think more tomorrow, but most probably no. The race is unlikely. We need perf_trace_event_init() or ":enable_event:this-event" right before trace_remove_event_call() takes the mutex. And right after the caller (kprobes) checks "disabled". > Hmm, what happens without this patch now? If it is active, and we delete > it? It will call back into the kprobes and access a tracepoint that does > not exist? Would this cause a crash? I think yes, the crash is possible. perf or FL_SOFT_MODE, this call/file has the external references, and we are going to free it. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
