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In MDEV-25936, we inadvertently introduced a problem that would cause safe_mutex failures in workloads that involve DDL on tables that contain FULLTEXT INDEX. The fix describes it best:
diff --git a/storage/innobase/fts/fts0fts.cc b/storage/innobase/fts/fts0fts.cc
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index 21a3567f33a..885b0432ebf 100644
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--- a/storage/innobase/fts/fts0fts.cc
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+++ b/storage/innobase/fts/fts0fts.cc
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@@ -1556,12 +1556,13 @@ static dberr_t fts_lock_table(trx_t *trx, const char *table_name)
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if (!--n)
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{
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err= DB_LOCK_WAIT_TIMEOUT;
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- break;
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+ goto fail;
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}
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std::this_thread::sleep_for(std::chrono::milliseconds(50));
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dict_sys.mutex_lock();
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}
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dict_sys.mutex_unlock();
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+fail:
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table->release();
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return err;
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}
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If a timeout occurs, we would wrongly attempt to release {{dict_sys.mutex}, which the current thread is not holding.
The failure would look something like this:
safe_mutex: Trying to unlock mutex mutex that wasn't locked at /data/Server/bb-10.6-MDEV-25919/storage/innobase/include/dict0dict.h, line 1570
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