Messages in this thread | | | Subject | Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload | From | Peter Zijlstra <> | Date | Mon, 24 Aug 2009 11:27:38 +0200 |
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On Mon, 2009-08-24 at 11:24 +0200, Ingo Molnar wrote: > * Peter Zijlstra <peterz@infradead.org> wrote: > > > On Mon, 2009-08-24 at 14:22 +0800, Li Zefan wrote: > > > Peter Zijlstra wrote: > > > > On Mon, 2009-08-24 at 12:19 +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.
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