Comment 16 for bug 1837430

Reviewed: https://review.opendev.org/672625
Committed: https://git.openstack.org/cgit/starlingx/integ/commit/?id=853388e615b6fb4fbec7fded3eb2652fe0120527
Submitter: Zuul
Branch: master

commit 853388e615b6fb4fbec7fded3eb2652fe0120527
Author: Bin Yang <email address hidden>
Date: Wed Jul 31 14:12:05 2019 +0800

    epoll: fix use-after-free in eventpoll_release_file

    back port upstream patch
    https://github.com/torvalds/linux/commit/ebe06187bf2aec10d537ce4595e416035367d703

    the epi is removed from list by list_del_rcu(&epi->fllink);
    under list_for_each_entry_rcu() without rcu_read_lock.

    if the rcu grace-period thread free epi before next list_for_each loop,
    the content of epi will be corrupted.

    Change-Id: I75dbf8ada5ca4734761efe260ca6d6f85886b180
    Closes-Bug: 1837430
    Suggested-by: <email address hidden>
    Signed-off-by: Bin Yang <email address hidden>