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MDEV-25113 introduced a race condition that we already fixed up in MDEV-26010. It turns out that this fix was not sufficient. The test innodb_zip.wl5522_debug_zip as well as the buffer pool resizing tests would still occasionally fail in debug builds due to a corruption of buf_pool.flush_list. The symptom would be that buf_pool.flush_list.count disagrees with the length of the linked list chain.
The race condition might be unobservable on single-socket IA-32 and AMD64 setups. I observed it on a dual Intel® Xeon® E5-2630. Adding more calls to buf_flush_validate_low() would seem to reduce the probability of failure.
The safe procedure for relocating a block in buf_pool.flush_list seems to be the following:
- Acquire buf_pool.mutex.
- Acquire the exclusive buf_pool.page_hash.latch.
- Acquire buf_pool.flush_list_mutex.
- Copy the block descriptor.
- Invoke buf_flush_relocate_on_flush_list().
- Release buf_pool.flush_list_mutex.
In this way, the relocated block descriptor should be guaranteed to be in a consistent state. At least the test innodb_zip.wl5522_debug_zip,16k no longer triggered the debug assertion on my system.
For the record, the debug assertion looks like this:
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10.6 61fcbed920c0ed1373725c4122af5a483ae7ffb2
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innodb_zip.wl5522_debug_zip '16k,innodb' w26 [ fail ]
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Test ended at 2021-07-21 14:08:52CURRENT_TEST: innodb_zip.wl5522_debug_zip
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mysqltest: At line 320: query 'UPDATE t1 SET c2 = c2 + c1' failed: <Unknown> (2013): Lost connection to server during query
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#5 0x000055a7aed68614 in ut_dbg_assertion_failed (expr=0x55a7af241007 "count == list.count", file=<optimized out>, line=<optimized out>, line@entry=467) at /mariadb/10.6/storage/innobase/ut/ut0dbg.cc:60
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#6 0x000055a7aedeba16 in ut_list_map<ut_list_base<buf_page_t, ut_list_node<buf_page_t> buf_page_t::*>, Check> (list=<optimized out>, functor=@0x7fc07cfef930: {<No data fields>}) at /mariadb/10.6/storage/innobase/include/ut0lst.h:467
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#7 ut_list_validate<ut_list_base<buf_page_t, ut_list_node<buf_page_t> buf_page_t::*>, Check> (list=<optimized out>, functor=@0x7fc07cfef930: {<No data fields>}) at /mariadb/10.6/storage/innobase/include/ut0lst.h:496
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#8 buf_flush_validate_low () at /mariadb/10.6/storage/innobase/buf/buf0flu.cc:2475
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#9 0x000055a7aedeab03 in buf_flush_validate_skip () at /mariadb/10.6/storage/innobase/buf/buf0flu.cc:124
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#10 buf_pool_t::insert_into_flush_list (this=0x55a7af831280 <buf_pool>, block=0x7fc07d36f578, lsn=158319367) at /mariadb/10.6/storage/innobase/buf/buf0flu.cc:204
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#11 0x000055a7aec166ad in buf_flush_note_modification (block=0x7fc07d36f578, start_lsn=158319367, end_lsn=158323907) at /mariadb/10.6/storage/innobase/include/buf0flu.ic:62
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#12 ReleaseBlocks::operator() (this=<optimized out>, this@entry=0x7fc07cfefa30, slot=slot@entry=0x7fc07cff01a8) at /mariadb/10.6/storage/innobase/mtr/mtr0mtr.cc:348
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#13 0x000055a7aec13481 in CIterate<ReleaseBlocks const>::operator() (this=0x7fc07cfefa30, block=<optimized out>) at /mariadb/10.6/storage/innobase/mtr/mtr0mtr.cc:61
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#14 mtr_buf_t::for_each_block_in_reverse<CIterate<ReleaseBlocks const> > (this=<optimized out>, this@entry=0x7fc07cff0160, functor=@0x7fc07cfefa30: {functor = {start = 158319367, end = 158323907, memo = @0x7fc07cff0160}}) at /mariadb/10.6/storage/innobase/include/dyn0buf.h:379
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#15 0x000055a7aec0ff3c in mtr_t::commit (this=<optimized out>) at /mariadb/10.6/storage/innobase/mtr/mtr0mtr.cc:444
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