MDEV-29622 Wrong assertions in lock_cancel_waiting_and_release() for …

…deadlock resolving caller

Suppose we have two transactions, trx 1 and trx 2.

trx 2 does deadlock resolving from lock_wait(), it sets
victim->lock.was_chosen_as_deadlock_victim=true for trx 1, but has not
yet invoked lock_cancel_waiting_and_release().

trx 1 checks the flag in lock_trx_handle_wait(), and starts rollback
from row_mysql_handle_errors(). It can change trx->lock.wait_thr and
trx->state as it holds trx_t::mutex, but trx 2 has not yet requested it,
as lock_cancel_waiting_and_release() has not yet been called.

After that trx 1 tries to release locks in trx_t::rollback_low(),
invoking trx_t::rollback_finish(). lock_release() is blocked on try to
acquire lock_sys.rd_lock(SRW_LOCK_CALL) in lock_release_try(), as
lock_sys is blocked by trx 2, as deadlock resolution works under
lock_sys.wr_lock(SRW_LOCK_CALL), see Deadlock::report() for details.

trx 2 executes lock_cancel_waiting_and_release() for deadlock victim, i.
e. for trx 1. lock_cancel_waiting_and_release() contains some
trx->lock.wait_thr and trx->state assertions, which will fail, because
trx 1 has changed them during rollback execution.

So, according to the above scenario, it's legal to have
trx->lock.wait_thr==0 and trx->state!=TRX_STATE_ACTIVE in
lock_cancel_waiting_and_release(), if it was invoked from
Deadlock::report(), and the fix is just in the assertion conditions
changing.

The fix is just in changing assertion condition.

There is also lock_wait() cleanup around trx->error_state.

If trx->error_state can be changed not by the owned thread, it must be
protected with lock_sys.wait_mutex, as lock_wait() uses trx->lock.cond
along with that mutex.

Also if trx->error_state was changed before lock_sys.wait_mutex
acquision, then it could be reset with the following code, what is
wrong. Also we need to check trx->error_state before entering waiting
loop, otherwise it can be the case when trx->error_state was set before
lock_sys.wait_mutex acquision, but the thread will be waiting on
trx->lock.cond.

mysql-test/suite/innodb/r/deadlock_wait_thr_race.result

@@ -0,0 +1,37 @@
+connect suspend_purge,localhost,root,,;
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+connection default;
+CREATE TABLE t (a int PRIMARY KEY, b int) engine = InnoDB;
+CREATE TABLE t2 (a int PRIMARY KEY) engine = InnoDB;
+INSERT INTO t VALUES (10, 10), (20, 20), (30, 30);
+INSERT INTO t2 VALUES (10), (20), (30);
+BEGIN;
+UPDATE t2 SET a = a + 100;
+SELECT * FROM t WHERE a = 20 FOR UPDATE;
+a	b
+20	20
+connect con_2,localhost,root,,;
+SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
+SET DEBUG_SYNC = 'lock_trx_handle_wait_enter SIGNAL upd_locked WAIT_FOR upd_cont';
+SET DEBUG_SYNC = 'trx_t_release_locks_enter SIGNAL sel_cont WAIT_FOR upd_cont_2';
+BEGIN;
+UPDATE t SET b = 100;
+connection default;
+SET DEBUG_SYNC="now WAIT_FOR upd_locked";
+SET DEBUG_SYNC="deadlock_report_before_lock_releasing SIGNAL upd_cont WAIT_FOR sel_cont";
+SET DEBUG_SYNC="lock_wait_before_suspend SIGNAL sel_before_suspend";
+SELECT * FROM t WHERE a = 10 FOR UPDATE;;
+connect con_3,localhost,root,,;
+SET DEBUG_SYNC="now WAIT_FOR sel_before_suspend";
+SET DEBUG_SYNC="now SIGNAL upd_cont_2";
+disconnect con_3;
+connection con_2;
+ERROR 40001: Deadlock found when trying to get lock; try restarting transaction
+disconnect con_2;
+connection default;
+a	b
+10	10
+SET DEBUG_SYNC = 'RESET';
+DROP TABLE t;
+DROP TABLE t2;
+disconnect suspend_purge;

mysql-test/suite/innodb/t/deadlock_wait_thr_race.test

@@ -0,0 +1,66 @@
+--source include/have_innodb.inc
+--source include/have_debug_sync.inc
+--source include/count_sessions.inc
+
+--connect(suspend_purge,localhost,root,,)
+# Purge can cause deadlock in the test, requesting page's RW_X_LATCH for trx
+# ids reseting, after trx 2 acqured RW_S_LATCH and suspended in debug sync point
+# lock_trx_handle_wait_enter, waiting for upd_cont signal, which must be
+# emitted after the last SELECT in this test. The last SELECT will hang waiting
+# for purge RW_X_LATCH releasing, and trx 2 will be rolled back by timeout.
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+
+--connection default
+CREATE TABLE t (a int PRIMARY KEY, b int) engine = InnoDB;
+CREATE TABLE t2 (a int PRIMARY KEY) engine = InnoDB;
+
+INSERT INTO t VALUES (10, 10), (20, 20), (30, 30);
+INSERT INTO t2 VALUES (10), (20), (30);
+
+BEGIN; # trx 1
+# The following update is necessary to increase the transaction weight, which is
+# calculated as the number of locks + the number of undo records during deadlock
+# report. Victim's transaction should have minimum weight. We need trx 2 to be
+# choosen as victim, that's why we need to increase the current transaction
+# weight.
+UPDATE t2 SET a = a + 100;
+SELECT * FROM t WHERE a = 20 FOR UPDATE;
+
+--connect(con_2,localhost,root,,)
+# RC is necessary to do semi-consistent read
+SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
+# It will be hit on trying to lock (20,20).
+SET DEBUG_SYNC = 'lock_trx_handle_wait_enter SIGNAL upd_locked WAIT_FOR upd_cont';
+SET DEBUG_SYNC = 'trx_t_release_locks_enter SIGNAL sel_cont WAIT_FOR upd_cont_2';
+BEGIN; # trx 2
+# We must not modify primary key fields to cause rr_sequential() read record
+# function choosing in mysql_update(), i.e. both query_plan.using_filesort and
+# query_plan.using_io_buffer must be false during init_read_record() call.
+# The following UPDATE will be chosen as deadlock victim and rolled back.
+--send UPDATE t SET b = 100
+
+--connection default
+SET DEBUG_SYNC="now WAIT_FOR upd_locked";
+SET DEBUG_SYNC="deadlock_report_before_lock_releasing SIGNAL upd_cont WAIT_FOR sel_cont";
+SET DEBUG_SYNC="lock_wait_before_suspend SIGNAL sel_before_suspend";
+# If the bug is not fixed, the following SELECT will crash, as the above UPDATE
+# will reset trx->lock.wait_thr during rollback
+--send SELECT * FROM t WHERE a = 10 FOR UPDATE;
+
+--connect(con_3,localhost,root,,)
+SET DEBUG_SYNC="now WAIT_FOR sel_before_suspend";
+SET DEBUG_SYNC="now SIGNAL upd_cont_2";
+--disconnect con_3
+
+--connection con_2
+--error ER_LOCK_DEADLOCK
+--reap
+--disconnect con_2
+
+--connection default
+--reap
+SET DEBUG_SYNC = 'RESET';
+DROP TABLE t;
+DROP TABLE t2;
+--disconnect suspend_purge
+--source include/wait_until_count_sessions.inc

storage/innobase/lock/lock0lock.cc

@@ -1789,8 +1789,8 @@ dberr_t lock_wait(que_thr_t *thr)
      wait_lock->un_member.tab_lock.table->id <= DICT_FIELDS_ID);
   thd_wait_begin(trx->mysql_thd, (type_mode & LOCK_TABLE)
                  ? THD_WAIT_TABLE_LOCK : THD_WAIT_ROW_LOCK);
-  trx->error_state= DB_SUCCESS;
 
+  int err= 0;
   mysql_mutex_lock(&lock_sys.wait_mutex);
   if (trx->lock.wait_lock)
   {
@@ -1812,26 +1812,24 @@ dberr_t lock_wait(que_thr_t *thr)
   if (row_lock_wait)
     lock_sys.wait_start();
 
-  trx->error_state= DB_SUCCESS;
-
 #ifdef HAVE_REPLICATION
   if (rpl)
     lock_wait_rpl_report(trx);
 #endif
 
+  if (trx->error_state != DB_SUCCESS)
+    goto check_trx_error;
+
   while (trx->lock.wait_lock)
   {
-    int err;
     DEBUG_SYNC_C("lock_wait_before_suspend");
 
     if (no_timeout)
-    {
       my_cond_wait(&trx->lock.cond, &lock_sys.wait_mutex.m_mutex);
-      err= 0;
-    }
     else
       err= my_cond_timedwait(&trx->lock.cond, &lock_sys.wait_mutex.m_mutex,
                              &abstime);
+check_trx_error:
     switch (trx->error_state) {
     case DB_DEADLOCK:
     case DB_INTERRUPTED:
@@ -1877,17 +1875,19 @@ dberr_t lock_wait(que_thr_t *thr)
 
 
 /** Resume a lock wait */
-static void lock_wait_end(trx_t *trx)
+template <bool from_deadlock= false>
+void lock_wait_end(trx_t *trx)
 {
   mysql_mutex_assert_owner(&lock_sys.wait_mutex);
   ut_ad(trx->mutex_is_owner());
   ut_d(const auto state= trx->state);
-  ut_ad(state == TRX_STATE_ACTIVE || state == TRX_STATE_PREPARED);
-  ut_ad(trx->lock.wait_thr);
+  ut_ad(state == TRX_STATE_COMMITTED_IN_MEMORY || state == TRX_STATE_ACTIVE ||
+        state == TRX_STATE_PREPARED);
+  ut_ad(from_deadlock || trx->lock.wait_thr);
 
   if (trx->lock.was_chosen_as_deadlock_victim)
   {
-    ut_ad(state == TRX_STATE_ACTIVE);
+    ut_ad(from_deadlock || state == TRX_STATE_ACTIVE);
     trx->error_state= DB_DEADLOCK;
   }
 
@@ -5674,13 +5674,16 @@ static void lock_release_autoinc_locks(trx_t *trx)
 }
 
 /** Cancel a waiting lock request and release possibly waiting transactions */
-static void lock_cancel_waiting_and_release(lock_t *lock)
+template <bool from_deadlock= false>
+void lock_cancel_waiting_and_release(lock_t *lock)
 {
   lock_sys.assert_locked(*lock);
   mysql_mutex_assert_owner(&lock_sys.wait_mutex);
   trx_t *trx= lock->trx;
   trx->mutex_lock();
-  ut_ad(trx->state == TRX_STATE_ACTIVE);
+  ut_d(const auto trx_state= trx->state);
+  ut_ad(trx_state == TRX_STATE_COMMITTED_IN_MEMORY ||
+        trx_state == TRX_STATE_ACTIVE);
 
   if (!lock->is_table())
     lock_rec_dequeue_from_page(lock, true);
@@ -5699,7 +5702,8 @@ static void lock_cancel_waiting_and_release(lock_t *lock)
   /* Reset the wait flag and the back pointer to lock in trx. */
   lock_reset_lock_and_trx_wait(lock);
 
-  lock_wait_end(trx);
+  lock_wait_end<from_deadlock>(trx);
+
   trx->mutex_unlock();
 }
 
@@ -6293,7 +6297,8 @@ namespace Deadlock
       /* victim->lock.was_chosen_as_deadlock_victim must always be set before
       releasing waiting locks and reseting trx->lock.wait_lock */
       victim->lock.was_chosen_as_deadlock_victim= true;
-      lock_cancel_waiting_and_release(victim->lock.wait_lock);
+      DEBUG_SYNC_C("deadlock_report_before_lock_releasing");
+      lock_cancel_waiting_and_release<true>(victim->lock.wait_lock);
 #ifdef WITH_WSREP
       if (victim->is_wsrep() && wsrep_thd_is_SR(victim->mysql_thd))
         wsrep_handle_SR_rollback(trx->mysql_thd, victim->mysql_thd);

storage/innobase/trx/trx0trx.cc

@@ -485,6 +485,7 @@ TRANSACTIONAL_INLINE inline void trx_t::commit_state()
 /** Release any explicit locks of a committing transaction. */
 inline void trx_t::release_locks()
 {
+  DEBUG_SYNC_C("trx_t_release_locks_enter");
   DBUG_ASSERT(state == TRX_STATE_COMMITTED_IN_MEMORY);
   DBUG_ASSERT(!is_referenced());