Messages in this thread | | | Subject | Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload | From | Peter Zijlstra <> | Date | Tue, 25 Aug 2009 08:21:06 +0200 |
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On Tue, 2009-08-25 at 13:22 +0800, Li Zefan wrote: > >>>>>> 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().
Basically avoid module unload when a tracepoint from that module has registered callbacks.
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