Comment 10 for bug 1838691

Reviewed: https://review.opendev.org/676195
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=e78b220f448c7eb0de35aafd1d49b00547384d41
Submitter: Zuul
Branch: stable/stein

commit e78b220f448c7eb0de35aafd1d49b00547384d41
Author: Sven Wegener <email address hidden>
Date: Fri Dec 14 12:56:49 2018 +0100

    Fix ceph: only close rbd image after snapshot iteration is finished

    list_snaps() returns an iterator object that requires resources from the
    Image object. Closing the Image object deallocates these resources.

    On Ceph mimic, which contains changes to the functions being invoked,
    iterating over the snapshots of a closed image results in the following
    assertion being triggered:

    cinder-backup[29383]: /build/ceph-13.2.2/src/common/Mutex.cc: In function 'void Mutex::Lock(bool)' thread 7f35a4812700 time 2018-12-14 10:10:49.843120
    cinder-backup[29383]: /build/ceph-13.2.2/src/common/Mutex.cc: 110: FAILED assert(r == 0)
    cinder-backup[29383]: ceph version 13.2.2 (02899bfda814146b021136e9d8e80eba494e1126) mimic (stable)
    cinder-backup[29383]: 1: (ceph::__ceph_assert_fail(char const*, char const*, int, char const*)+0x102) [0x7f35903440f2]
    cinder-backup[29383]: 2: (()+0x3162b7) [0x7f35903442b7]
    cinder-backup[29383]: 3: (Mutex::Lock(bool)+0x1de) [0x7f359031901e]
    cinder-backup[29383]: 4: (()+0x8f452) [0x7f358dafc452]
    cinder-backup[29383]: 5: (()+0x11280d) [0x7f358db7f80d]
    cinder-backup[29383]: 6: (rbd_snap_get_namespace_type()+0x29) [0x7f358dacf549]

    The lock being tried to acquire and the object that contained it have
    already been destroyed by closing the image. The assertion terminates
    the cinder-backup service via SIGABRT.

    On Ceph luminous we've seen occasional segfaults of the cinder-backup
    service, which might have the same underlying cause.

    Closes-Bug: #1838691

    Change-Id: If6043d82cc57d9247a290816d90b95cdf719eaac
    Signed-off-by: Sven Wegener <email address hidden>
    (cherry picked from commit 76569672599eda764f946ad6ee2ce0bdaddad36b)