Created attachment 15935 [details]
set of log files.

Trying to do a time machine backup to a smb share from MacOSX 10.15.4 I receive a kernel panic.

On "normal" shares I get a normal behavior. On samba 4.11.x there was everything okay.

Steps I did to reproduce the issue:
0. Delete time machine backup in MacOS X app.
1. Stop smb server.
2. clean logs.
3. start smb server.
4. connect with the Time Machine app in MacOS 10.15.4.
4.1. choose share (FileVault) from list in Time Machine app.
4.2. type credentials.
4.3. receive segfault.
5. stop smb server.

I received:
[2020/04/12 11:15:21.535160,  0] ../../lib/dbwrap/dbwrap.c:82(dbwrap_record_get_value)
 PANIC: assert failed at ../../lib/dbwrap/dbwrap.c(82): rec->value_valid
[2020/04/12 11:15:21.535322,  0] ../../source3/lib/util.c:830(smb_panic_s3)
 PANIC (pid 1707): assert failed: rec->value_valid
[2020/04/12 11:15:21.536138,  0] ../../lib/util/fault.c:265(log_stack_trace)
 BACKTRACE: 37 stack frames:
  #0 /usr/lib/samba/amd64/libsamba-util.so.0.0.1'log_stack_trace+0x26 [0xfffffd7fee51de66]
  #1 /usr/lib/samba/amd64/libsmbconf.so.0'smb_panic_s3+0x26 [0xfffffd7fedf5a596]
  #2 /usr/lib/samba/amd64/libsamba-util.so.0.0.1'smb_panic+0x1f [0xfffffd7fee51df3f]
  #3 /usr/lib/samba/private/amd64/libdbwrap-samba4.so'dbwrap_record_get_value+0x2a [0xfffffd7fece2627a]
  #4 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'get_share_mode_lock+0x109 [0xfffffd7fee7195c9]
  #5 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_contend_level2_oplocks_begin+0xa1 [0xfffffd7fee7f7761]
  #6 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'brl_lock+0x635 [0xfffffd7fee710f45]
  #7 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'do_lock_fn+0xa4 [0xfffffd7fee70d534]
  #8 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'share_mode_do_locked_fn+0x86 [0xfffffd7fee7174b6]
  #9 /usr/lib/samba/amd64/libsmbconf.so.0'dbwrap_watched_do_locked_fn+0xfa [0xfffffd7fedf622ca]
  #10 /usr/lib/samba/private/amd64/libdbwrap-samba4.so'db_tdb_do_locked+0x12f [0xfffffd7fece295cf]
  #11 /usr/lib/samba/private/amd64/libdbwrap-samba4.so'dbwrap_do_locked+0x48 [0xfffffd7fece269a8]
  #12 /usr/lib/samba/amd64/libsmbconf.so.0'dbwrap_watched_do_locked+0x6f [0xfffffd7fedf60d7f]
  #13 /usr/lib/samba/private/amd64/libdbwrap-samba4.so'dbwrap_do_locked+0x48 [0xfffffd7fece269a8]
  #14 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'share_mode_do_locked+0xd2 [0xfffffd7fee719b82]
  #15 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'do_lock+0xf0 [0xfffffd7fee70dfe0]
  #16 /usr/lib/samba/amd64/vfs/fruit.so'fruit_create_file+0x7ba [0xfffffd7fe88a55aa]
  #17 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_smb2_request_process_create+0xa07 [0xfffffd7fee7d3237]
  #18 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_smb2_request_dispatch+0xc8f [0xfffffd7fee7c985f]
  #19 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_smb2_connection_handler+0x621 [0xfffffd7fee7ca7e1]
  #20 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'tevent_common_invoke_fd_handler+0x80 [0xfffffd7fecfca580]
  #21 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'epoll_event_loop_once+0x22c [0xfffffd7fecfd180c]
  #22 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'std_event_loop_once+0x40 [0xfffffd7fecfcf8f0]
  #23 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'_tevent_loop_once+0x95 [0xfffffd7fecfc9bd5]
  #24 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'tevent_common_loop_wait+0x23 [0xfffffd7fecfc9e43]
  #25 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'std_event_loop_wait+0x40 [0xfffffd7fecfcf870]
  #26 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_process+0x777 [0xfffffd7fee7b8677]
  #27 /usr/lib/samba/sbin/amd64/smbd'smbd_accept_connection+0x189 [0x40d5b9]
  #28 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'tevent_common_invoke_fd_handler+0x80 [0xfffffd7fecfca580]
  #29 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'epoll_event_loop_once+0x22c [0xfffffd7fecfd180c]
  #30 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'std_event_loop_once+0x40 [0xfffffd7fecfcf8f0]
  #31 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'_tevent_loop_once+0x95 [0xfffffd7fecfc9bd5]
  #32 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'tevent_common_loop_wait+0x23 [0xfffffd7fecfc9e43]
  #33 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'std_event_loop_wait+0x40 [0xfffffd7fecfcf870]
  #34 /usr/lib/samba/sbin/amd64/smbd'main+0x1a0f [0x40f9ff]
  #35 /usr/lib/samba/sbin/amd64/smbd'_start_crt+0x83 [0x408e73]
  #36 /usr/lib/samba/sbin/amd64/smbd'_start+0x18 [0x408dd8]
[2020/04/12 11:15:21.538230,  0] ../../source3/lib/dumpcore.c:315(dump_core)
 dumping core in /var/samba/log/cores/smbd

Complete set of logs with log level 10 is attached.