Messages in this thread |  | | | Date | Thu, 27 Aug 2009 12:03:42 -0400 (EDT) | | From | Steven Rostedt <> | | Subject | Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload |
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On Thu, 27 Aug 2009, Mathieu Desnoyers wrote: > > > > For this race to occur, the probe (code that hooks to the tracepoint) must > > be in module that does not contain the tracepoint. We don't even need more > > than one module, this could occur even with a core tracepoint. If a module > > registers it, if it unregisters before unloading, the tracepoint may be > > hit before the unregister and executing while the module is unloading. > > > > I don't think we need to worry about this with the case of TRACE_EVENT and > > ftrace.h. The reason is that the trace point and probes are always in the > > same location. The MACROS set up the probe code with the modules. Thus, to > > remove the module, you must also remove the tracepoint itself along with > > the probe. If you can be executing in the probe, then you must have hit > > the trace point. If you hit the trace point, then you are executing code > > inside the module you are removing, which is a bug in the module code > > itself. > > > > Using the ftrace.h MACROS limits the use of tracepoints and this race > > does not exist. I feel we are safe not needing to have the > > tracepoint_synchronize_unregister within the ftrace.h code. > > > > Looks right. If you can guarantee that the probe is only called from > tracepoints located within the same module as the probe, you should be > safe without tracepoint_synchronize_unregister. It's worth adding a > comment in ftrace.h explaining that though.
Yeah, I tried to trick the code to see if I can get a probe in another module than the trace point, and I get nothing but linking errors. I'm sure if I work hard enough, I may trick it to do so, but if anyone does that, I'll slap a big fat NAK on it ;-)
OK, I modify my fix to add a comment to this effect.
Thanks,
-- Steve
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