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Commit74aaa21

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Fix race condition in CheckTargetForConflictsIn.
Dan Ports
1 parent6b449d9 commit74aaa21

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1 file changed

+79
-128
lines changed

1 file changed

+79
-128
lines changed

‎src/backend/storage/lmgr/predicate.c

Lines changed: 79 additions & 128 deletions
Original file line numberDiff line numberDiff line change
@@ -3638,6 +3638,8 @@ CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag)
36383638
LWLockIdpartitionLock;
36393639
PREDICATELOCKTARGET*target;
36403640
PREDICATELOCK*predlock;
3641+
PREDICATELOCK*mypredlock=NULL;
3642+
PREDICATELOCKTAGmypredlocktag;
36413643

36423644
Assert(MySerializableXact!=InvalidSerializableXact);
36433645

@@ -3683,139 +3685,21 @@ CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag)
36833685
if (sxact==MySerializableXact)
36843686
{
36853687
/*
3686-
* If we're getting a write lock onthe tuple and we're not in a
3687-
*subtransaction, we don't needa predicate (SIREAD) lock. We
3688-
*can't use this optimization within a subtransaction because the
3689-
*subtransaction could be rolled back, and we would be left
3690-
*without any lock at the top level.
3688+
* If we're getting a write lock ona tuple, we don't need
3689+
* a predicate (SIREAD) lock on the same tuple. We can
3690+
*safely remove our SIREAD lock, but we'll defer doing so
3691+
*until after the loop because that requires upgrading to
3692+
*an exclusive partition lock.
36913693
*
3692-
* At this point our transaction already has an ExclusiveRowLock
3693-
* on the relation, so we are OK to drop the predicate lock on the
3694-
* tuple, if found, without fearing that another write against the
3695-
* tuple will occur before the MVCC information makes it to the
3696-
* buffer.
3694+
* We can't use this optimization within a subtransaction
3695+
* because the subtransaction could roll back, and we
3696+
* would be left without any lock at the top level.
36973697
*/
36983698
if (!IsSubTransaction()
36993699
&&GET_PREDICATELOCKTARGETTAG_OFFSET(*targettag))
37003700
{
3701-
uint32predlockhashcode;
3702-
PREDICATELOCKTARGET*rmtarget=NULL;
3703-
PREDICATELOCK*rmpredlock;
3704-
LOCALPREDICATELOCK*locallock,
3705-
*rmlocallock;
3706-
3707-
/*
3708-
* This is a tuple on which we have a tuple predicate lock. We
3709-
* only have shared LW locks now; release those, and get
3710-
* exclusive locks only while we modify things.
3711-
*/
3712-
LWLockRelease(SerializableXactHashLock);
3713-
LWLockRelease(partitionLock);
3714-
LWLockAcquire(SerializablePredicateLockListLock,LW_SHARED);
3715-
LWLockAcquire(partitionLock,LW_EXCLUSIVE);
3716-
LWLockAcquire(SerializableXactHashLock,LW_EXCLUSIVE);
3717-
3718-
/*
3719-
* Remove the predicate lock from shared memory, if it wasn't
3720-
* removed while the locks were released. One way that could
3721-
* happen is from autovacuum cleaning up an index.
3722-
*/
3723-
predlockhashcode=PredicateLockHashCodeFromTargetHashCode
3724-
(&(predlock->tag),targettaghash);
3725-
rmpredlock= (PREDICATELOCK*)
3726-
hash_search_with_hash_value(PredicateLockHash,
3727-
&(predlock->tag),
3728-
predlockhashcode,
3729-
HASH_FIND,NULL);
3730-
if (rmpredlock)
3731-
{
3732-
Assert(rmpredlock==predlock);
3733-
3734-
SHMQueueDelete(predlocktargetlink);
3735-
SHMQueueDelete(&(predlock->xactLink));
3736-
3737-
rmpredlock= (PREDICATELOCK*)
3738-
hash_search_with_hash_value(PredicateLockHash,
3739-
&(predlock->tag),
3740-
predlockhashcode,
3741-
HASH_REMOVE,NULL);
3742-
Assert(rmpredlock==predlock);
3743-
3744-
RemoveTargetIfNoLongerUsed(target,targettaghash);
3745-
3746-
LWLockRelease(SerializableXactHashLock);
3747-
LWLockRelease(partitionLock);
3748-
LWLockRelease(SerializablePredicateLockListLock);
3749-
3750-
locallock= (LOCALPREDICATELOCK*)
3751-
hash_search_with_hash_value(LocalPredicateLockHash,
3752-
targettag,targettaghash,
3753-
HASH_FIND,NULL);
3754-
3755-
/*
3756-
* Remove entry in local lock table if it exists and has
3757-
* no children. It's OK if it doesn't exist; that means
3758-
* the lock was transferred to a new target by a different
3759-
* backend.
3760-
*/
3761-
if (locallock!=NULL)
3762-
{
3763-
locallock->held= false;
3764-
3765-
if (locallock->childLocks==0)
3766-
{
3767-
rmlocallock= (LOCALPREDICATELOCK*)
3768-
hash_search_with_hash_value(LocalPredicateLockHash,
3769-
targettag,targettaghash,
3770-
HASH_REMOVE,NULL);
3771-
Assert(rmlocallock==locallock);
3772-
}
3773-
}
3774-
3775-
DecrementParentLocks(targettag);
3776-
3777-
/*
3778-
* If we've cleaned up the last of the predicate locks for
3779-
* the target, bail out before re-acquiring the locks.
3780-
*/
3781-
if (rmtarget)
3782-
return;
3783-
3784-
/*
3785-
* The list has been altered. Start over at the front.
3786-
*/
3787-
LWLockAcquire(partitionLock,LW_SHARED);
3788-
nextpredlock= (PREDICATELOCK*)
3789-
SHMQueueNext(&(target->predicateLocks),
3790-
&(target->predicateLocks),
3791-
offsetof(PREDICATELOCK,targetLink));
3792-
3793-
LWLockAcquire(SerializableXactHashLock,LW_SHARED);
3794-
}
3795-
else
3796-
{
3797-
/*
3798-
* The predicate lock was cleared while we were attempting
3799-
* to upgrade our lightweight locks. Revert to the shared
3800-
* locks.
3801-
*/
3802-
LWLockRelease(SerializableXactHashLock);
3803-
LWLockRelease(partitionLock);
3804-
LWLockRelease(SerializablePredicateLockListLock);
3805-
LWLockAcquire(partitionLock,LW_SHARED);
3806-
3807-
/*
3808-
* The list may have been altered by another process while
3809-
* we weren't holding the partition lock. Start over at
3810-
* the front.
3811-
*/
3812-
nextpredlock= (PREDICATELOCK*)
3813-
SHMQueueNext(&(target->predicateLocks),
3814-
&(target->predicateLocks),
3815-
offsetof(PREDICATELOCK,targetLink));
3816-
3817-
LWLockAcquire(SerializableXactHashLock,LW_SHARED);
3818-
}
3701+
mypredlock=predlock;
3702+
mypredlocktag=predlock->tag;
38193703
}
38203704
}
38213705
elseif (!SxactIsRolledBack(sxact)
@@ -3849,6 +3733,73 @@ CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag)
38493733
}
38503734
LWLockRelease(SerializableXactHashLock);
38513735
LWLockRelease(partitionLock);
3736+
3737+
/*
3738+
* If we found one of our own SIREAD locks to remove, remove it
3739+
* now.
3740+
*
3741+
* At this point our transaction already has an ExclusiveRowLock
3742+
* on the relation, so we are OK to drop the predicate lock on the
3743+
* tuple, if found, without fearing that another write against the
3744+
* tuple will occur before the MVCC information makes it to the
3745+
* buffer.
3746+
*/
3747+
if (mypredlock!=NULL)
3748+
{
3749+
uint32predlockhashcode;
3750+
PREDICATELOCK*rmpredlock;
3751+
3752+
LWLockAcquire(SerializablePredicateLockListLock,LW_SHARED);
3753+
LWLockAcquire(partitionLock,LW_EXCLUSIVE);
3754+
LWLockAcquire(SerializableXactHashLock,LW_EXCLUSIVE);
3755+
3756+
/*
3757+
* Remove the predicate lock from shared memory, if it wasn't
3758+
* removed while the locks were released. One way that could
3759+
* happen is from autovacuum cleaning up an index.
3760+
*/
3761+
predlockhashcode=PredicateLockHashCodeFromTargetHashCode
3762+
(&mypredlocktag,targettaghash);
3763+
rmpredlock= (PREDICATELOCK*)
3764+
hash_search_with_hash_value(PredicateLockHash,
3765+
&mypredlocktag,
3766+
predlockhashcode,
3767+
HASH_FIND,NULL);
3768+
if (rmpredlock!=NULL)
3769+
{
3770+
Assert(rmpredlock==mypredlock);
3771+
3772+
SHMQueueDelete(&(mypredlock->targetLink));
3773+
SHMQueueDelete(&(mypredlock->xactLink));
3774+
3775+
rmpredlock= (PREDICATELOCK*)
3776+
hash_search_with_hash_value(PredicateLockHash,
3777+
&mypredlocktag,
3778+
predlockhashcode,
3779+
HASH_REMOVE,NULL);
3780+
Assert(rmpredlock==mypredlock);
3781+
3782+
RemoveTargetIfNoLongerUsed(target,targettaghash);
3783+
}
3784+
3785+
LWLockRelease(SerializableXactHashLock);
3786+
LWLockRelease(partitionLock);
3787+
LWLockRelease(SerializablePredicateLockListLock);
3788+
3789+
if (rmpredlock!=NULL)
3790+
{
3791+
/*
3792+
* Remove entry in local lock table if it exists. It's OK
3793+
* if it doesn't exist; that means the lock was
3794+
* transferred to a new target by a different backend.
3795+
*/
3796+
hash_search_with_hash_value(LocalPredicateLockHash,
3797+
targettag,targettaghash,
3798+
HASH_REMOVE,NULL);
3799+
3800+
DecrementParentLocks(targettag);
3801+
}
3802+
}
38523803
}
38533804

38543805
/*

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