Description of problem:
The rbd-mirror daemon crashes frequently when running rbd_mirror_group_simple.sh


The crash is in the group_replayer::Replayer:

 ceph version 19.3.0-9130-gc3f7c4d064f (c3f7c4d064ff5129b353bdce21c285011a661446) tentacle (dev) 
 1: /lib64/libc.so.6(+0x3e930) [0x7f5e55302930]
 2: /lib64/libc.so.6(+0x8bdac) [0x7f5e5534fdac]
 3: raise()
 4: abort()
 5: /lib64/libstdc++.so.6(+0xa1b21) [0x7f5e55648b21]
 6: /lib64/libstdc++.so.6(+0xad52c) [0x7f5e5565452c]
 7: /lib64/libstdc++.so.6(+0xad597) [0x7f5e55654597]
 8: /lib64/libstdc++.so.6(+0xad7f9) [0x7f5e556547f9]
 9: (ceph::mutex_debug_detail::mutex_debug_impl<false>::lock(bool)+0xd4) [0x555b004fd6f6]
 10: (rbd::mirror::group_replayer::Replayer<librbd::ImageCtx>::unlink_group_snapshots()+0x38d) [0x555b00603435]
 11: (rbd::mirror::group_replayer::Replayer<librbd::ImageCtx>::handle_load_remote_group_snapshots(int)+0xe6) [0x555b006051f6]
 12: (LambdaContext<rbd::mirror::group_replayer::Replayer<librbd::ImageCtx>::load_remote_group_snapshots()::{lambda(int)#2}>::finish(int)+0xd) [0x555b00605707]
 13: (Context::complete(int)+0x9) [0x555b0050d599]
 14: (librbd::group::ListSnapshotsRequest<librbd::ImageCtx>::finish(int)+0x40) [0x555b0085d48a]
 15: (librbd::group::ListSnapshotsRequest<librbd::ImageCtx>::sort_snaps()+0x598) [0x555b0085ed6c]
 16: (librbd::group::ListSnapshotsRequest<librbd::ImageCtx>::handle_list_snaps(int)+0x5ae) [0x555b0085f324]
 17: (void librbd::util::detail::rados_callback<librbd::group::ListSnapshotsRequest<librbd::ImageCtx>, &librbd::group::ListSnapshotsRequest<librbd::ImageCtx>::handle_list_snaps>(void*, void*)+0x13) [0x555b0085f679]
 18: /work/ceph/build/lib/librados.so.2(+0xb4f04) [0x7f5e57190f04]
 19: /work/ceph/build/lib/librados.so.2(+0xb737a) [0x7f5e5719337a]
 20: /work/ceph/build/lib/librados.so.2(+0xca10b) [0x7f5e571a610b]
 21: /work/ceph/build/lib/librados.so.2(+0xcb4c8) [0x7f5e571a74c8]
 22: /work/ceph/build/lib/librados.so.2(+0xcfdf9) [0x7f5e571abdf9]
 23: /lib64/libstdc++.so.6(+0xdbad4) [0x7f5e55682ad4]
 24: /lib64/libc.so.6(+0x8a062) [0x7f5e5534e062]
 25: /lib64/libc.so.6(+0x10f0e0) [0x7f5e553d30e0]


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


How reproducible:


Steps to Reproduce:
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Actual results:


Expected results:


Additional info:

The callback is attempting to access the Replayer object which has already been deleted as part of GroupReplayer::shut_down().