MDEV-18225 Avoid use of LOCK_prepared_stmt_count mutex in Statement_map destructo
This mutex can be freed when server shuts down (when thread_count goes down to 0) , but it is still used inside THD::~THD() when Statement_map is destroyed. The fix is to call Statement_map::reset() at the point where thread_count is still positive, and avoid locking LOCK_prepared_stmt_count in THD destructor.
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@ -1518,6 +1518,7 @@ void THD::cleanup(void)
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sp_cache_clear(&sp_func_cache);
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mysql_ull_cleanup(this);
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stmt_map.reset();
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/* All metadata locks must have been released by now. */
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DBUG_ASSERT(!mdl_context.has_locks());
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@ -3777,11 +3778,13 @@ void Statement_map::erase(Statement *statement)
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void Statement_map::reset()
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{
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/* Must be first, hash_free will reset st_hash.records */
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mysql_mutex_lock(&LOCK_prepared_stmt_count);
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DBUG_ASSERT(prepared_stmt_count >= st_hash.records);
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prepared_stmt_count-= st_hash.records;
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mysql_mutex_unlock(&LOCK_prepared_stmt_count);
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if (st_hash.records)
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{
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mysql_mutex_lock(&LOCK_prepared_stmt_count);
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DBUG_ASSERT(prepared_stmt_count >= st_hash.records);
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prepared_stmt_count-= st_hash.records;
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mysql_mutex_unlock(&LOCK_prepared_stmt_count);
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}
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my_hash_reset(&names_hash);
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my_hash_reset(&st_hash);
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last_found_statement= 0;
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@ -3790,12 +3793,8 @@ void Statement_map::reset()
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Statement_map::~Statement_map()
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{
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/* Must go first, hash_free will reset st_hash.records */
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mysql_mutex_lock(&LOCK_prepared_stmt_count);
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DBUG_ASSERT(prepared_stmt_count >= st_hash.records);
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prepared_stmt_count-= st_hash.records;
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mysql_mutex_unlock(&LOCK_prepared_stmt_count);
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/* Statement_map::reset() should be called prior to destructor. */
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DBUG_ASSERT(!st_hash.records);
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my_hash_free(&names_hash);
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my_hash_free(&st_hash);
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}
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