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MDEV-18225 Avoid use of LOCK_prepared_stmt_count mutex in Statement_map destructo

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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.
This commit is contained in:
Vladislav Vaintroub 2019-01-14 13:09:27 +01:00
parent 7372fe4da1
commit 7d3161def8
1 changed files with 10 additions and 11 deletions
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21
sql/sql_class.cc
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@ -1518,6 +1518,7 @@ void THD::cleanup(void)
sp_cache_clear(&sp_func_cache);
mysql_ull_cleanup(this);
stmt_map.reset();
/* All metadata locks must have been released by now. */
DBUG_ASSERT(!mdl_context.has_locks());
@ -3777,11 +3778,13 @@ void Statement_map::erase(Statement *statement)
void Statement_map::reset()
{
/* Must be first, hash_free will reset st_hash.records */
mysql_mutex_lock(&LOCK_prepared_stmt_count);
DBUG_ASSERT(prepared_stmt_count >= st_hash.records);
prepared_stmt_count-= st_hash.records;
mysql_mutex_unlock(&LOCK_prepared_stmt_count);
if (st_hash.records)
{
mysql_mutex_lock(&LOCK_prepared_stmt_count);
DBUG_ASSERT(prepared_stmt_count >= st_hash.records);
prepared_stmt_count-= st_hash.records;
mysql_mutex_unlock(&LOCK_prepared_stmt_count);
}
my_hash_reset(&names_hash);
my_hash_reset(&st_hash);
last_found_statement= 0;
@ -3790,12 +3793,8 @@ void Statement_map::reset()
Statement_map::~Statement_map()
{
/* Must go first, hash_free will reset st_hash.records */
mysql_mutex_lock(&LOCK_prepared_stmt_count);
DBUG_ASSERT(prepared_stmt_count >= st_hash.records);
prepared_stmt_count-= st_hash.records;
mysql_mutex_unlock(&LOCK_prepared_stmt_count);
/* Statement_map::reset() should be called prior to destructor. */
DBUG_ASSERT(!st_hash.records);
my_hash_free(&names_hash);
my_hash_free(&st_hash);
}