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Commit96d2df8

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Fix VM buffer pin management in heap_lock_updated_tuple_rec().
Sloppy coding in this function could lead to leaking a VM buffer pin,or to attempting to free the same pin twice. Repair. While at it,reduce the code's tendency to free and reacquire the same page pin.Back-patch to 9.6; before that, this routine did not concern itselfwith VM pages.Amit Kapila and Tom LaneDiscussion:https://postgr.es/m/CAA4eK1KJKwhc=isgTQHjM76CAdVswzNeAuZkh_cx-6QgGkSEgA@mail.gmail.com
1 parent529137c commit96d2df8

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1 file changed

+16
-8
lines changed

1 file changed

+16
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lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 16 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -5661,6 +5661,7 @@ heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
56615661
new_xmax;
56625662
TransactionIdpriorXmax=InvalidTransactionId;
56635663
boolcleared_all_frozen= false;
5664+
boolpinned_desired_page;
56645665
Buffervmbuffer=InvalidBuffer;
56655666
BlockNumberblock;
56665667

@@ -5682,7 +5683,8 @@ heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
56825683
* chain, and there's no further tuple to lock: return success to
56835684
* caller.
56845685
*/
5685-
returnHeapTupleMayBeUpdated;
5686+
result=HeapTupleMayBeUpdated;
5687+
gotoout_unlocked;
56865688
}
56875689

56885690
l4:
@@ -5695,9 +5697,12 @@ heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
56955697
* to recheck after we have the lock.
56965698
*/
56975699
if (PageIsAllVisible(BufferGetPage(buf)))
5700+
{
56985701
visibilitymap_pin(rel,block,&vmbuffer);
5702+
pinned_desired_page= true;
5703+
}
56995704
else
5700-
vmbuffer=InvalidBuffer;
5705+
pinned_desired_page=false;
57015706

57025707
LockBuffer(buf,BUFFER_LOCK_EXCLUSIVE);
57035708

@@ -5706,8 +5711,13 @@ heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
57065711
* all visible while we were busy locking the buffer, we'll have to
57075712
* unlock and re-lock, to avoid holding the buffer lock across I/O.
57085713
* That's a bit unfortunate, but hopefully shouldn't happen often.
5714+
*
5715+
* Note: in some paths through this function, we will reach here
5716+
* holding a pin on a vm page that may or may not be the one matching
5717+
* this page. If this page isn't all-visible, we won't use the vm
5718+
* page, but we hold onto such a pin till the end of the function.
57095719
*/
5710-
if (vmbuffer==InvalidBuffer&&PageIsAllVisible(BufferGetPage(buf)))
5720+
if (!pinned_desired_page&&PageIsAllVisible(BufferGetPage(buf)))
57115721
{
57125722
LockBuffer(buf,BUFFER_LOCK_UNLOCK);
57135723
visibilitymap_pin(rel,block,&vmbuffer);
@@ -5733,8 +5743,8 @@ heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
57335743
*/
57345744
if (TransactionIdDidAbort(HeapTupleHeaderGetXmin(mytup.t_data)))
57355745
{
5736-
UnlockReleaseBuffer(buf);
5737-
returnHeapTupleMayBeUpdated;
5746+
result=HeapTupleMayBeUpdated;
5747+
gotoout_locked;
57385748
}
57395749

57405750
old_infomask=mytup.t_data->t_infomask;
@@ -5941,20 +5951,18 @@ heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
59415951
priorXmax=HeapTupleHeaderGetUpdateXid(mytup.t_data);
59425952
ItemPointerCopy(&(mytup.t_data->t_ctid),&tupid);
59435953
UnlockReleaseBuffer(buf);
5944-
if (vmbuffer!=InvalidBuffer)
5945-
ReleaseBuffer(vmbuffer);
59465954
}
59475955

59485956
result=HeapTupleMayBeUpdated;
59495957

59505958
out_locked:
59515959
UnlockReleaseBuffer(buf);
59525960

5961+
out_unlocked:
59535962
if (vmbuffer!=InvalidBuffer)
59545963
ReleaseBuffer(vmbuffer);
59555964

59565965
returnresult;
5957-
59585966
}
59595967

59605968
/*

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