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SubjectRe: [PATCH 2/3] tracing/profile: add ref count for registering profile events
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On Fri, 2009-09-11 at 16:09 +0200, Peter Zijlstra wrote:
> On Fri, 2009-09-11 at 16:04 +0200, Peter Zijlstra wrote:
> > On Fri, 2009-09-11 at 09:54 -0400, Steven Rostedt wrote:
> >
> > > +#ifdef MODULE
> > > +# define event_trace_up_ref() \
> > > + do { \
> > > + if (!try_module_get(THIS_MODULE)) { \
> > > + atomic_dec(&event_call->profile_count); \
> > > + return -ENOENT; \
> > > + } \
> > > + } while (0)
> > > +# define event_trace_down_ref() module_put(THIS_MODULE)
> > > +#else
> > > +# define event_trace_up_ref() do { } while (0)
> > > +# define event_trace_down_ref() do { } while (0)
> > > +#endif
> >
> > That's like truely gruesomely ugly.
> >
> > At the very least write it like:
> >
> > int event_trace_up_ref(struct ftrace_event_call *call)
> > {
> > if (!try_module_get(THIS_MODULE)) {
> > atomic_dev(&call->profile_count);
> > return -ENOENT;
> > }
> > return 0;
> > }
>
> Or we can go with Li's original patch, that was less ugly.

Here's another version of the patch (less ugly). I forgot that the
try_module_get should handle code compiled with !CONFIG_MODULE.
This should be less ugly.

-- Steve

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 308bafd..6d5edd1 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -409,16 +409,23 @@ static int ftrace_profile_enable_##call(struct ftrace_event_call *event_call) \
{ \
int ret = 0; \
\
- if (!atomic_inc_return(&event_call->profile_count)) \
+ if (!atomic_inc_return(&event_call->profile_count)) { \
+ if (!try_module_get(THIS_MODULE)) \
+ goto out_fail; \
ret = register_trace_##call(ftrace_profile_##call); \
+ } \
\
return ret; \
+ out_fail: \
+ atomic_dec(&event_call->profile_count); \
} \
\
static void ftrace_profile_disable_##call(struct ftrace_event_call *event_call)\
{ \
- if (atomic_add_negative(-1, &event_call->profile_count)) \
+ if (atomic_add_negative(-1, &event_call->profile_count)) { \
unregister_trace_##call(ftrace_profile_##call); \
+ module_put(THIS_MODULE) \
+ } \
}

#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)



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