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Commit4d2a844

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Allow callback functions to deregister themselves during a call.
Fetch the next-item pointer before the call not after, so thatwe aren't dereferencing a dangling pointer if the callbackderegistered itself during the call. The risky coding patternappears in CallXactCallbacks, CallSubXactCallbacks, andResourceOwnerReleaseInternal. (There are some other places thatmight be at hazard if they offered deregistration functionality,but they don't.)I (tgl) considered back-patching this, but desisted because itwouldn't be very safe for extensions to rely on this working inpre-v16 branches.Hao WuDiscussion:https://postgr.es/m/CAH+9SWXTiERkmhRke+QCcc+jRH8d5fFHTxh8ZK0-Yn4BSpyaAg@mail.gmail.com
1 parentd84a7b2 commit4d2a844

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2 files changed

+18
-3
lines changed

2 files changed

+18
-3
lines changed

‎src/backend/access/transam/xact.c

Lines changed: 12 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3656,9 +3656,14 @@ static void
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CallXactCallbacks(XactEventevent)
36573657
{
36583658
XactCallbackItem*item;
3659+
XactCallbackItem*next;
36593660

3660-
for (item=Xact_callbacks;item;item=item->next)
3661+
for (item=Xact_callbacks;item;item=next)
3662+
{
3663+
/* allow callbacks to unregister themselves when called */
3664+
next=item->next;
36613665
item->callback(event,item->arg);
3666+
}
36623667
}
36633668

36643669

@@ -3713,9 +3718,14 @@ CallSubXactCallbacks(SubXactEvent event,
37133718
SubTransactionIdparentSubid)
37143719
{
37153720
SubXactCallbackItem*item;
3721+
SubXactCallbackItem*next;
37163722

3717-
for (item=SubXact_callbacks;item;item=item->next)
3723+
for (item=SubXact_callbacks;item;item=next)
3724+
{
3725+
/* allow callbacks to unregister themselves when called */
3726+
next=item->next;
37183727
item->callback(event,mySubid,parentSubid,item->arg);
3728+
}
37193729
}
37203730

37213731

‎src/backend/utils/resowner/resowner.c

Lines changed: 6 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -501,6 +501,7 @@ ResourceOwnerReleaseInternal(ResourceOwner owner,
501501
ResourceOwnerchild;
502502
ResourceOwnersave;
503503
ResourceReleaseCallbackItem*item;
504+
ResourceReleaseCallbackItem*next;
504505
Datumfoundres;
505506

506507
/* Recurse to handle descendants */
@@ -701,8 +702,12 @@ ResourceOwnerReleaseInternal(ResourceOwner owner,
701702
}
702703

703704
/* Let add-on modules get a chance too */
704-
for (item=ResourceRelease_callbacks;item;item=item->next)
705+
for (item=ResourceRelease_callbacks;item;item=next)
706+
{
707+
/* allow callbacks to unregister themselves when called */
708+
next=item->next;
705709
item->callback(phase,isCommit,isTopLevel,item->arg);
710+
}
706711

707712
CurrentResourceOwner=save;
708713
}

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