Description of problem:
commit 448ce0e enbales ignore_missing_thread on perf stat, but perf may still return sys_perf_event_open failure with 3(No such process) when stating multiple events since commit 448ce0e only set ignore_missing_thread flag on the first evsel, and when thread dies between opening following events, perf will fail with 3.

link to commit 448ce0e: https://github.com/torvalds/linux/commit/448ce0e6ea93ae99e0b36055e5f5a3f723fe3665#diff-aa5d9c1b58d3c6129afb0d4cb977d806a218039836bd565102f26e2be3e11859

Version-Release number of selected component (if applicable):


How reproducible:
use perf to stat multiple (e.g. more than 100) events on a multi-threaded (e.g. more than 100 threads) process which frequently create and end threads,


Steps to Reproduce:
1. use perf to stat multiple (e.g. more than 100) events on a multi-threaded (e.g. more than 100 threads) process which frequently create and end threads
2. and you may see perf return sys_perf_event_open failure with 3(No such process)
3. you can use strace perf stat [args] may make the bug easier to reproduce as perf runs much slower with strace attaching on it

Actual results:
perf return sys_perf_event_open failure with 3(No such process)


Expected results:
perf continue monitoring the remaining threads and do not exit with
error.


Additional info: