Messages in this thread | | | Date | Tue, 25 Aug 2009 14:33:14 +0800 | From | Li Zefan <> | Subject | Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload |
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>>>>>>>> If the correspoding module is unloaded before ftrace_profile_disable() >>>>>>>> is called, event->profile_disable() won't be called, which can >>>>>>>> cause oops: >>>>>>>> >>>>>>>> # insmod trace-events-sample.ko >>>>>>>> # perf record -f -a -e sample:foo_bar sleep 3 & >>>>>>>> # sleep 1 >>>>>>>> # rmmod trace_events_sample >>>>>>>> # insmod trace-events-sample.ko >>>>>>>> OOPS! >>>>>>>> >>>>>>>> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> >>>>>>> Hrmm, feel fragile, why don't we check if all a modules tracepoints are >>>>>>> unused on unload? >>>>>>> >>>>>> I don't think it's fragile. We are profiling via a module's >>>>>> tracepoint, so we should pin the module, via module_get(). >>>>>> If event->profile_enable() has been calld, we should make >>>>>> sure it's profile_disable() will be called. >>>>> What I call fragile is that everyone registering a tracepoint >>>>> callback will now apparently need to worry about modules, _that_ >>>>> is fragile. >>>>> >>>>> Either make module unload look at tracepoint users, or place the >>>>> try_get_module() in the registration hooks so that regular users >>>>> don't need to worry about it. >>>> The bug found by Li needs to be fixed obviously. >>>> >>>> I tend to agree with you that this does not appear to be the best >>>> place to do it: so you suggest to implicitly increase the module >>>> refcount on callback registr instead? (and releasing it when >>>> unregistering) >>>> >>>> Same end result, slightly cleaner place to bump the refcount. >>> Yes, because the user of tracepoints should never need to care about >>> modules. >>> >> I'm afraid it is not feasible to bump module refcnt implicitly >> in tracepoint_probe_register(). >> >> If a tracepoint is registered in module_init, and unregistered >> in module_exit (see sample/tracepoints), the module is unloadable: >> >> insmod >> ->call mod->init() >> ->trace_reg_foo() >> ->module_get() >> >> rmmod >> ->check mod refcnt >> ->call mod->exit() >> ->trace_unreg_foo() >> ->module_put() > > Not tracepoint_probe_{un,}register(), in {un,}register_trace_$call(). >
Is there any difference?
static inline int register_trace_##name(void (*probe)(proto)) \ { \ int ret; \ void (*func)(void) = reg; \ \ ret = tracepoint_probe_register(#name, (void *)probe); \ if (func && !ret) \ func(); \ return ret; \ }
> Basically avoid module unload when a tracepoint from that module has > registered callbacks.
TRACE_EVENT() won't prevent this. Instead at module unload, a module notifier callback will be called to unregistread those tracepoint callbacks.
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