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MDEV-29635 race on trx->lock.wait_lock in deadlock resolution

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Returning DB_SUCCESS unconditionally if !trx->lock.wait_lock in
lock_trx_handle_wait() is wrong. Because even if
trx->lock.was_chosen_as_deadlock_victim was not set before the first check
in lock_trx_handle_wait(), it can be set after
the check, and trx->lock.wait_lock can be reset by another thread from
lock_reset_lock_and_trx_wait() if the transaction was chosen as deadlock
victim. In this case lock_trx_handle_wait() will return DB_SUCCESS even
the transaction was marked as deadlock victim, and continue execution
instead of rolling back.

The fix is to check trx->lock.was_chosen_as_deadlock_victim once more if
trx->lock.wait_lock is reset, as trx->lock.wait_lock can be reset only
after trx->lock.was_chosen_as_deadlock_victim was set if the transaction
was chosen as deadlock victim.
This commit is contained in:
Vlad Lesin
2022-10-06 16:54:00 +03:00
parent ab0190101b
commit acebe35719
4 changed files with 105 additions and 1 deletions
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31
mysql-test/suite/innodb/r/deadlock_wait_lock_race.result Normal file
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@@ -0,0 +1,31 @@
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;
BEGIN;
SET DEBUG_SYNC = 'lock_trx_handle_wait_before_unlocked_wait_lock_check SIGNAL upd_locked WAIT_FOR upd_cont';
UPDATE t SET b = 100;
connection default;
SET DEBUG_SYNC="now WAIT_FOR upd_locked";
SET DEBUG_SYNC="lock_wait_before_suspend SIGNAL upd_cont";
SELECT * FROM t WHERE a = 10 FOR UPDATE;
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;

62
mysql-test/suite/innodb/t/deadlock_wait_lock_race.test Normal file
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@@ -0,0 +1,62 @@
--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;
BEGIN; # trx 2
# The first time it will be hit on trying to lock (20,20), the second hit
# will be on (30,30).
SET DEBUG_SYNC = 'lock_trx_handle_wait_before_unlocked_wait_lock_check SIGNAL upd_locked WAIT_FOR upd_cont';
# 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.
--send UPDATE t SET b = 100
--connection default
SET DEBUG_SYNC="now WAIT_FOR upd_locked";
SET DEBUG_SYNC="lock_wait_before_suspend SIGNAL upd_cont";
--send SELECT * FROM t WHERE a = 10 FOR UPDATE
--connection con_2
# If the bug is not fixed, lock_trx_handle_wait() wrongly returns DB_SUCCESS
# instead of DB_DEADLOCK, row_search_mvcc() of trx 2 behaves so as if (20,20)
# was locked. Some debug assertion must crash the server. If the bug is fixed,
# trx 2 must just be rolled back by deadlock detector.
--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

11
storage/innobase/lock/lock0lock.cc
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@@ -1822,6 +1822,7 @@ dberr_t lock_wait(que_thr_t *thr)
while (trx->lock.wait_lock)
{
int err;
DEBUG_SYNC_C("lock_wait_before_suspend");
if (no_timeout)
{
@@ -5869,6 +5870,7 @@ lock_unlock_table_autoinc(
/** Handle a pending lock wait (DB_LOCK_WAIT) in a semi-consistent read
while holding a clustered index leaf page latch.
@param trx transaction that is or was waiting for a lock
@retval DB_SUCCESS if the lock was granted
@retval DB_DEADLOCK if the transaction must be aborted due to a deadlock
@@ -5879,8 +5881,13 @@ dberr_t lock_trx_handle_wait(trx_t *trx)
DEBUG_SYNC_C("lock_trx_handle_wait_enter");
if (trx->lock.was_chosen_as_deadlock_victim)
return DB_DEADLOCK;
DEBUG_SYNC_C("lock_trx_handle_wait_before_unlocked_wait_lock_check");
/* trx->lock.was_chosen_as_deadlock_victim must always be set before
trx->lock.wait_lock if the transaction was chosen as deadlock victim,
the function must not return DB_SUCCESS if
trx->lock.was_chosen_as_deadlock_victim is set. */
if (!trx->lock.wait_lock)
return DB_SUCCESS;
return trx->lock.was_chosen_as_deadlock_victim ? DB_DEADLOCK : DB_SUCCESS;
dberr_t err= DB_SUCCESS;
mysql_mutex_lock(&lock_sys.wait_mutex);
if (trx->lock.was_chosen_as_deadlock_victim)
@@ -6283,6 +6290,8 @@ namespace Deadlock
ut_ad(victim->state == TRX_STATE_ACTIVE);
/* 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);
#ifdef WITH_WSREP

2
storage/innobase/row/row0sel.cc
View File

@@ -5270,6 +5270,8 @@ no_gap_lock:
switch (err) {
case DB_SUCCESS:
ut_ad(
!trx->lock.was_chosen_as_deadlock_victim);
/* The lock was granted while we were
searching for the last committed version.
Do a normal locking read. */