FYI, we noticed the following commit:


https://github.com/0day-ci/linux David-Carrillo-Cisneros/remove-unnecessary-IPI-reading-uncore-events/20160818-045857

commit 412929295ff670aa6890e346e2fc05f58d93cd96 ("perf/core: check return value of perf_event_read IPI")

Hi Xiaolong,

The problem was discussed following the submission:
https://lkml.org/lkml/2016/8/21/58

and it was decided to revert the WARN_ON and purposely ignore the error in smp_call_function_single: 
http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?id=58763148758057ffc447bf990321d3ea86d199a0

David