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SubjectRe: ftrace/perf_event leak
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On Wed, 2010-09-01 at 11:42 +0300, Avi Kivity wrote:
> I recently added perf_event support to kvm_stat, to display kvm
> tracepoints as statistics (I'd like to fold this to tools/perf
> eventually, but that's another story). However I'm seeing a resource
> leak - after I quit the tool, there are quite a few references into the
> kvm module:
>
> kvm_intel 43655 0
> kvm 272984 269 kvm_intel
>
> The tool is just a python script that reads
> /sys/kernel/debug/tracing/events/kvm to find out which events are
> available, uses perf_event_open() to create one group per cpu to which a
> lot of events are attached. The only special thing I can think of is
> that we use an ioctl to attach a filter to many perf_event descriptors.
>
> You can find the source at
> http://git.kernel.org/?p=virt/kvm/qemu-kvm.git;a=blob_plain;f=kvm/kvm_stat;hb=5bd5f131b50cb373ff4e2a3632c6dad00a1f0b55.
> All it needs are the kvm modules loaded; no need to actually run a
> guest. Run as root.
>

Does something like the below cure that?

I seem to remember C doesn't make any promises about the order of logic
statements, hence we need to explicitly pull out that try_module_get()
so that it evaluates after the rest of the conditions.

---
kernel/trace/trace_event_perf.c | 10 ++++++----
1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 000e6e8..35051f2 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -88,10 +88,11 @@ int perf_trace_init(struct perf_event *p_event)
mutex_lock(&event_mutex);
list_for_each_entry(tp_event, &ftrace_events, list) {
if (tp_event->event.type == event_id &&
- tp_event->class && tp_event->class->reg &&
- try_module_get(tp_event->mod)) {
- ret = perf_trace_event_init(tp_event, p_event);
- break;
+ tp_event->class && tp_event->class->reg) {
+ if (try_module_get(tp_event->mod)) {
+ ret = perf_trace_event_init(tp_event, p_event);
+ break;
+ }
}
}
mutex_unlock(&event_mutex);
@@ -138,6 +139,7 @@ void perf_trace_destroy(struct perf_event *p_event)

free_percpu(tp_event->perf_events);
tp_event->perf_events = NULL;
+ module_put(tp_event->mod);

if (!--total_ref_count) {
for (i = 0; i < 4; i++) {


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