Assertion failure: buf0flu.ic:98:block->page.flush_observer == nullptr || block->page.flush_observer == observer || observer == nullptr

This crash is seen during pstress runs with default_table_encryption set to either ONLINE_TO_KEYRING or ONLINE_FROM_KEYRING_TO_UNENCRYPTED
It is a very frequent crash seen in almost every alternate run.

Stacktrace:
==========

#0 __pthread_kill (threadid=<optimized out>, signo=6) at ../sysdeps/unix/sysv/linux/pthread_kill.c:62
#1 0x000000000468db39 in my_write_core (sig=6) at /home/mohit.joshi/mysql-8.0/mysys/stacktrace.cc:308
#2 0x00000000035d9382 in handle_fatal_signal (sig=6) at /home/mohit.joshi/mysql-8.0/sql/signal_handler.cc:174
#3 <signal handler called>
#4 0x00007fa69b299438 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
#5 0x00007fa69b29b03a in __GI_abort () at abort.c:89
#6 0x0000000004af4b93 in ut_dbg_assertion_failed (expr=0x66227c8 "block->page.flush_observer == nullptr || block->page.flush_observer == observer || observer == nullptr", file=0x6622690 "/home/mohit.joshi/mysql-8.0/storage/innobase/include/buf0flu.ic", line=98) at /home/mohit.joshi/mysql-8.0/storage/innobase/ut/ut0dbg.cc:98
#7 0x0000000004921861 in buf_flush_note_modification (block=0x7fa677c06100, start_lsn=0, end_lsn=0, observer=0x7fa5881270b0) at /home/mohit.joshi/mysql-8.0/storage/innobase/include/buf0flu.ic:98
#8 0x0000000004921cc0 in Add_dirty_blocks_to_flush_list::add_dirty_page_to_flush_list (this=0x7fa68c2e8b10, slot=0x7fa5881415f8) at /home/mohit.joshi/mysql-8.0/storage/innobase/mtr/mtr0mtr.cc:253
#9 0x0000000004921d0f in Add_dirty_blocks_to_flush_list::operator() (this=0x7fa68c2e8b10, slot=0x7fa5881415f8) at /home/mohit.joshi/mysql-8.0/storage/innobase/mtr/mtr0mtr.cc:263
#10 0x00000000049226a1 in Iterate<Add_dirty_blocks_to_flush_list>::operator() (this=0x7fa68c2e8b08, block=0x7fa5881415d8) at /home/mohit.joshi/mysql-8.0/storage/innobase/mtr/mtr0mtr.cc:78
#11 0x0000000004922262 in dyn_buf_t<512ul>::for_each_block_in_reverse<Iterate<Add_dirty_blocks_to_flush_list> > (this=0x7fa5881415a0, functor=...) at /home/mohit.joshi/mysql-8.0/storage/innobase/include/dyn0buf.h:324
#12 0x00000000049208aa in mtr_t::Command::add_dirty_blocks_to_flush_list (this=0x7fa68c2e8bc0, start_lsn=0, end_lsn=0) at /home/mohit.joshi/mysql-8.0/storage/innobase/mtr/mtr0mtr.cc:623
#13 0x0000000004920a8d in mtr_t::Command::execute (this=0x7fa68c2e8bc0) at /home/mohit.joshi/mysql-8.0/storage/innobase/mtr/mtr0mtr.cc:664
#14 0x0000000004920183 in mtr_t::commit (this=0x7fa5881415a0) at /home/mohit.joshi/mysql-8.0/storage/innobase/mtr/mtr0mtr.cc:485
#15 0x0000000004b81b8e in PageBulk::commit (this=0x7fa58804fb70, success=true) at /home/mohit.joshi/mysql-8.0/storage/innobase/btr/btr0bulk.cc:346
#16 0x0000000004b82aee in BtrBulk::pageCommit (this=0x7fa588146980, page_bulk=0x7fa58804fb70, next_page_bulk=0x7fa58810f9c0, insert_father=true) at /home/mohit.joshi/mysql-8.0/storage/innobase/btr/btr0bulk.cc:754
#17 0x0000000004b83009 in BtrBulk::prepareSpace (this=0x7fa588146980, page_bulk=@0x7fa68c2e8d18: 0x7fa58804fb70, level=0, rec_size=82) at /home/mohit.joshi/mysql-8.0/storage/innobase/btr/btr0bulk.cc:867
#18 0x0000000004b835ee in BtrBulk::insert (this=0x7fa588146980, tuple=0x7fa5885e3b28, level=0) at /home/mohit.joshi/mysql-8.0/storage/innobase/btr/btr0bulk.cc:996
#19 0x0000000004988c80 in BtrBulk::insert (this=0x7fa588146980, tuple=0x7fa5885e3b28) at /home/mohit.joshi/mysql-8.0/storage/innobase/include/btr0bulk.h:324
#20 0x00000000049b8f30 in row_merge_insert_index_tuples (trx=0x7fa68d141f08, index=0x7fa5880728e0, old_table=0x7fa5c0c97ee0, fd=-1, block=0x0, crypt_block=0x0, space_id=5, row_buf=0x7fa588106760, btr_bulk=0x7fa588146980, stage=0x0) at /home/mohit.joshi/mysql-8.0/storage/innobase/row/row0merge.cc:3240
#21 0x00000000049b62c7 in row_merge_read_clustered_index (trx=0x7fa68d141f08, table=0x7fa588071b00, old_table=0x7fa5c0c97ee0, new_table=0x7fa588126700, online=true, index=0x7fa5881135d0, fts_sort_idx=0x0, psort_info=0x0, files=0x7fa5881146d0, key_numbers=0x7fa588113618, n_index=5, add_cols=0x0, add_v=0x0, col_map=0x7fa588113800, add_autoinc=18446744073709551615, sequence=..., block=0x7fa6840fd000 <error: Cannot access memory at address 0x7fa6840fd000>, crypt_block=0x0, skip_pk_sort=true, tmpfd=0x7fa68c2ea02c, stage=0x7fa588114650, eval_table=0x7fa588071b00, prebuilt=0x7fa588100e70) at /home/mohit.joshi/mysql-8.0/storage/innobase/row/row0merge.cc:2288
#22 0x00000000049bab25 in row_merge_build_indexes (trx=0x7fa68d141f08, old_table=0x7fa5c0c97ee0, new_table=0x7fa588126700, online=true, indexes=0x7fa5881135d0, key_numbers=0x7fa588113618, n_indexes=5, table=0x7fa588071b00, add_cols=0x0, col_map=0x7fa588113800, add_autoinc=18446744073709551615, sequence=..., skip_pk_sort=true, stage=0x7fa588114650, add_v=0x0, eval_table=0x7fa588071b00, prebuilt=0x7fa588100e70) at /home/mohit.joshi/mysql-8.0/storage/innobase/row/row0merge.cc:3869
#23 0x0000000004839f5a in ha_innobase::inplace_alter_table_impl<dd::Table> (this=0x7fa588039518, altered_table=0x7fa588071b00, ha_alter_info=0x7fa68c2eb110, old_dd_tab=0x7fa5ac0347f8, new_dd_tab=0x7fa58813eb18) at /home/mohit.joshi/mysql-8.0/storage/innobase/handler/handler0alter.cc:6240
#24 0x0000000004814be9 in ha_innobase::inplace_alter_table (this=0x7fa588039518, altered_table=0x7fa588071b00, ha_alter_info=0x7fa68c2eb110, old_dd_tab=0x7fa5ac0347f8, new_dd_tab=0x7fa58813eb18) at /home/mohit.joshi/mysql-8.0/storage/innobase/handler/handler0alter.cc:1297
#25 0x0000000002fbbaa9 in handler::ha_inplace_alter_table (this=0x7fa588039518, altered_table=0x7fa588071b00, ha_alter_info=0x7fa68c2eb110, old_table_def=0x7fa5ac0347f8, new_table_def=0x7fa58813eb18) at /home/mohit.joshi/mysql-8.0/sql/handler.h:5905
#26 0x00000000034bad84 in mysql_inplace_alter_table (thd=0x7fa588000da0, schema=..., new_schema=..., table_def=0x7fa5ac0347f8, altered_table_def=0x7fa58813eb18, table_list=0x7fa5881216b8, table=0x7fa588165bc0, altered_table=0x7fa588071b00, ha_alter_info=0x7fa68c2eb110, inplace_supported=HA_ALTER_INPLACE_NO_LOCK_AFTER_PREPARE, alter_ctx=0x7fa68c2ec020, columns=..., fk_key_info=0x7fa58816ae50, fk_key_count=0, fk_invalidator=0x7fa68c2ebf50) at /home/mohit.joshi/mysql-8.0/sql/sql_table.cc:12857
#27 0x00000000034c74b0 in mysql_alter_table (thd=0x7fa588000da0, new_db=0x0, new_name=0x0, create_info=0x7fa68c2ed930, table_list=0x7fa5881216b8, alter_info=0x7fa68c2ed7b0) at /home/mohit.joshi/mysql-8.0/sql/sql_table.cc:16967
#28 0x00000000034cbf61 in mysql_recreate_table (thd=0x7fa588000da0, table_list=0x7fa5881216b8, table_copy=false) at /home/mohit.joshi/mysql-8.0/sql/sql_table.cc:18289
#29 0x00000000032e84bb in mysql_admin_table (thd=0x7fa588000da0, tables=0x7fa5881216b8, check_opt=0x7fa5880043d0, operator_name=0x52fa09e "optimize", lock_type=TL_WRITE, open_for_modify=false, repair_table_use_frm=false, extra_open_options=0, prepare_func=0x0, operator_func=(int (handler::*)(handler * const, THD *, HA_CHECK_OPT )) 0x2fdc7e2 <handler::ha_optimize(THD, HA_CHECK_OPT*)>, check_view=0, alter_info=0x7fa588121518, need_to_acquire_shared_backup_lock=true) at /home/mohit.joshi/mysql-8.0/sql/sql_admin.cc:1127
#30 0x00000000032e9fab in Sql_cmd_optimize_table::execute (this=0x7fa588121c78, thd=0x7fa588000da0) at /home/mohit.joshi/mysql-8.0/sql/sql_admin.cc:1598
#31 0x00000000033f1eb0 in mysql_execute_command (thd=0x7fa588000da0, first_level=true) at /home/mohit.joshi/mysql-8.0/sql/sql_parse.cc:4706
#32 0x00000000033f48cd in mysql_parse (thd=0x7fa588000da0, parser_state=0x7fa68c2efb80, update_userstat=false) at /home/mohit.joshi/mysql-8.0/sql/sql_parse.cc:5530
#33 0x00000000033e95c2 in dispatch_command (thd=0x7fa588000da0, com_data=0x7fa68c2f0d00, command=COM_QUERY) at /home/mohit.joshi/mysql-8.0/sql/sql_parse.cc:1826
#34 0x00000000033e7b3a in do_command (thd=0x7fa588000da0) at /home/mohit.joshi/mysql-8.0/sql/sql_parse.cc:1303
#35 0x00000000035c32cc in handle_connection (arg=0x9d22a50) at /home/mohit.joshi/mysql-8.0/sql/conn_handler/connection_handler_per_thread.cc:308
#36 0x0000000004e1206f in pfs_spawn_thread (arg=0xb5893a0) at /home/mohit.joshi/mysql-8.0/storage/perfschema/pfs.cc:2855
#37 0x00007fa69d4f56ba in start_thread (arg=0x7fa68c2f1700) at pthread_create.c:333
#38 0x00007fa69b36b4dd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Steps to reproduce:
===================
./pstress-ps --database=test --threads=20 --queries-per-thread=100000 --logdir=/tmp/079507/1 --user=root --socket=/tmp/079507/1/socket.sock --seed 079507 --step 1 --metadata-path /home/mohit.joshi/test_p/079507/ --seconds 100 --tables 10 --records 500 --log-all-queries --log-failed-queries --mso=default_table_encryption=ON=OFF=ONLINE_TO_KEYRING=ONLINE_FROM_KEYRING_TO_UNENCRYPTED --mso=innodb_encryption_threads=0=4 --mso=innodb_file_per_table=ON=OFF --alter-algorith --alter-table-encrypt-inplace 50 --alter-table-encrypt 50 --modify-column 50 --alter-table-compress 50 --add-column 50 --drop-column 50 --drop-index 50 --add-index 50 --rename-column 50 --delete-with-cond 5 --update-with-cond 5 --select-single-row 1