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Commiteb706fd

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Fix newly introduced bug in slab.c
d21ded7 changed the way slab.c works but introduced a bug that meant wecould end up with the slab's curBlocklistIndex pointing to the wrong list.The condition which was checking for this was failing to account for twothings:1. The curBlocklistIndex could be 0 as we've currently got no non-fullblocks to put chunks on. In this case, the dlist_is_empty() check cannotbe performed as there can be any number of completely full blocks at thatindex.2. The curBlocklistIndex may be greater than the index we just moved theblock onto. Since we need to ensure we fill up fuller blocks first, wemust reset curBlocklistIndex when changing any blocklist element that'sless than the curBlocklistIndex too.Reported-by: Takamichi OsumiDiscussion:https://postgr.es/m/TYCPR01MB8373329C6329768D7E093D68EDEB9@TYCPR01MB8373.jpnprd01.prod.outlook.com
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‎src/backend/utils/mmgr/slab.c

Lines changed: 11 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -691,16 +691,20 @@ SlabFree(void *pointer)
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dlist_push_head(&slab->blocklist[newBlocklistIdx],&block->node);
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/*
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*It's possible that we've no blocks in the blocklist at the
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*curBlocklistIndex position. When this happens we must find the
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*next blocklist index which contains blocks. We can be certain
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*we'll find a block as at leastonemust exist for the chunk we're
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*currently freeing.
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*The blocklist[curBlocklistIdx] may now be empty or we may now be
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*able to use a lower-element blocklist. We'll need to redetermine
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*what the slab->curBlocklistIndex is if the current blocklist was
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*changed or if a lower elementonewas changed. We must ensure we
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*use the list with the fullest block(s).
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*/
700-
if (slab->curBlocklistIndex==curBlocklistIdx&&
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dlist_is_empty(&slab->blocklist[curBlocklistIdx]))
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if (slab->curBlocklistIndex >=curBlocklistIdx)
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{
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slab->curBlocklistIndex=SlabFindNextBlockListIndex(slab);
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/*
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* We know there must be a block with at least 1 unused chunk as
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* we just pfree'd one. Ensure curBlocklistIndex reflects this.
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*/
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Assert(slab->curBlocklistIndex>0);
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}
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}

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