test/fops failing with reference count change

    1: 10 threads on table:__wt

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==6515==ERROR: AddressSanitizer: heap-use-after-free on address 0x61b00006b390 at pc 0x50a8cd bp 0x7faebbd74b20 sp 0x7faebbd74b18

READ of size 4 at 0x61b00006b390 thread T18

    #0 0x50a8cc in __wt_conn_btree_close /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/conn/conn_dhandle.c:580

    WT-1 0x490db6 in __wt_session_discard_btree /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/session/session_dhandle.c:433

    WT-2 0x488307 in __wt_spin_trylock_func /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/session/session_api.c:39

    WT-3 0x488307 in __session_close /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/session/session_api.c:84

    WT-4 0x4372fd in obj_upgrade /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/test/fops/../../../test/fops/file.c:145

    WT-5 0x437d84 in fop /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/test/fops/../../../test/fops/fops.c:152

    WT-6 0x42ea73 in __asan::AsanThread::ThreadStart(unsigned long) (/home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/test/fops/t+0x42ea73)

    WT-7 0x3fea607d14 in start_thread (/lib64/libpthread.so.0+0x3fea607d14)

    WT-8 0x3fe9af253c in __clone (/lib64/libc.so.6+0x3fe9af253c)

0x61b00006b390 is located 16 bytes inside of 1464-byte region [0x61b00006b380,0x61b00006b938)

freed by thread T20 here:

    #0 0x428414 in free (/home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/test/fops/t+0x428414)

    WT-1 0x50aead in __wt_conn_dhandle_discard_single /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/conn/conn_dhandle.c:698

    WT-2 0x508dc6 in __conn_dhandle_sweep /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/conn/conn_dhandle.c:404

    WT-3 0x508dc6 in __wt_conn_btree_get /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/conn/conn_dhandle.c:431

    WT-4 0x490587 in __wt_spin_trylock_func /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/session/session_dhandle.c:306

    WT-5 0x490587 in __wt_session_get_btree /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/session/session_dhandle.c:364

    WT-6 0x4615a1 in __wt_metadata_open /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/meta/meta_table.c:42

    WT-7 0x4615a1 in __wt_metadata_cursor /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/meta/meta_table.c:65

    WT-8 0x480a42 in __wt_schema_open_table /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/schema/schema_open.c:346

    WT-9 0x47d201 in __wt_spin_trylock_func /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/schema/schema_list.c:20

    WT-10 0x47d201 in __wt_schema_get_table /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/schema/schema_list.c:87

    WT-11 0x47a299 in __create_table /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/schema/schema_create.c:468

    WT-12 0x47a299 in __wt_schema_create /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/schema/schema_create.c:582

    WT-13 0x48983c in __session_create /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/../src/session/session_api.c:324

    WT-14 0x436d16 in obj_create /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/test/fops/../../../test/fops/file.c:89

    WT-15 0x437cb3 in fop /home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/test/fops/../../../test/fops/fops.c:136

    WT-16 0x42ea73 in __asan::AsanThread::ThreadStart(unsigned long) (/home/jenkins/jenkins/workspace/wiredtiger-clang-sanitizer/build_posix/test/fops/t+0x42ea73)