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Commit126552c

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Fix race in SSI interaction with gin fast path.
The ginfast.c code previously checked for conflicts in before lockingthe relevant buffer, leaving a window where a RW conflict could bemissed. Re-order.There was also a place where buffer ID and block number were confusedwhile trying to predicate-lock a page, noted by visual inspection.Back-patch to all supported releases. Fixes one more problem discoveredwith the reproducer from bug #17949, in this case when Dmitry triedother index types.Reported-by: Artem Anisimov <artem.anisimov.255@gmail.com>Reported-by: Dmitry Dolgov <9erthalion6@gmail.com>Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>Discussion:https://postgr.es/m/17949-a0f17035294a55e2%40postgresql.org
1 parentbcc93a3 commit126552c

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2 files changed

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-3
lines changed

2 files changed

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lines changed

‎src/backend/access/gin/ginfast.c

Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -245,9 +245,10 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
245245
/*
246246
* An insertion to the pending list could logically belong anywhere in the
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* tree, so it conflicts with all serializable scans. All scans acquire a
248-
* predicate lock on the metabuffer to represent that.
248+
* predicate lock on the metabuffer to represent that. Therefore we'll
249+
* check for conflicts in, but not until we have the page locked and are
250+
* ready to modify the page.
249251
*/
250-
CheckForSerializableConflictIn(index,NULL,GIN_METAPAGE_BLKNO);
251252

252253
if (collector->sumsize+collector->ntuples*sizeof(ItemIdData)>GinListPageSize)
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{
@@ -291,6 +292,8 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
291292
LockBuffer(metabuffer,GIN_EXCLUSIVE);
292293
metadata=GinPageGetMeta(metapage);
293294

295+
CheckForSerializableConflictIn(index,NULL,GIN_METAPAGE_BLKNO);
296+
294297
if (metadata->head==InvalidBlockNumber)
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{
296299
/*
@@ -353,6 +356,8 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
353356
char*ptr;
354357
char*collectordata;
355358

359+
CheckForSerializableConflictIn(index,NULL,GIN_METAPAGE_BLKNO);
360+
356361
buffer=ReadBuffer(index,metadata->tail);
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LockBuffer(buffer,GIN_EXCLUSIVE);
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page=BufferGetPage(buffer);

‎src/backend/access/gin/ginget.c

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -140,7 +140,9 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
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* Predicate lock entry leaf page, following pages will be locked by
141141
* moveRightIfItNeeded()
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*/
143-
PredicateLockPage(btree->index,stack->buffer,snapshot);
143+
PredicateLockPage(btree->index,
144+
BufferGetBlockNumber(stack->buffer),
145+
snapshot);
144146

145147
for (;;)
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{

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