oprofile: fix race condition in event_buffer free
Looking at the 2.6.31-rc9 code, it appears there is a race condition in the event_buffer cleanup code path (shutdown). This could lead to kernel panic as some CPUs may be operating on the event buffer AFTER it has been freed. The attached patch solves the problem and makes sure CPUs check if the buffer is not NULL before they access it as some may have been spinning on the mutex while the buffer was being freed. The race may happen if the buffer is freed during pending reads. But it is not clear why there are races in add_event_entry() since all workqueues or handlers are canceled or flushed before the event buffer is freed. Signed-off-by: NDavid Rientjes <rientjes@google.com> Signed-off-by: NStephane Eranian <eranian@google.com> Signed-off-by: NRobert Richter <robert.richter@amd.com>
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