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Commit255a925

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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 parent17b8887 commit255a925

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2 files changed

+10
-3
lines changed

2 files changed

+10
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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
@@ -244,9 +244,10 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
244244
/*
245245
* 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
247-
* predicate lock on the metabuffer to represent that.
247+
* predicate lock on the metabuffer to represent that. Therefore we'll
248+
* check for conflicts in, but not until we have the page locked and are
249+
* ready to modify the page.
248250
*/
249-
CheckForSerializableConflictIn(index,NULL,metabuffer);
250251

251252
if (collector->sumsize+collector->ntuples*sizeof(ItemIdData)>GinListPageSize)
252253
{
@@ -290,6 +291,8 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
290291
LockBuffer(metabuffer,GIN_EXCLUSIVE);
291292
metadata=GinPageGetMeta(metapage);
292293

294+
CheckForSerializableConflictIn(index,NULL,metabuffer);
295+
293296
if (metadata->head==InvalidBlockNumber)
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{
295298
/*
@@ -352,6 +355,8 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
352355
char*ptr;
353356
char*collectordata;
354357

358+
CheckForSerializableConflictIn(index,NULL,metabuffer);
359+
355360
buffer=ReadBuffer(index,metadata->tail);
356361
LockBuffer(buffer,GIN_EXCLUSIVE);
357362
page=BufferGetPage(buffer);

‎src/backend/access/gin/ginget.c

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -139,7 +139,9 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
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* Predicate lock entry leaf page, following pages will be locked by
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* moveRightIfItNeeded()
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*/
142-
PredicateLockPage(btree->index,stack->buffer,snapshot);
142+
PredicateLockPage(btree->index,
143+
BufferGetBlockNumber(stack->buffer),
144+
snapshot);
143145

144146
for (;;)
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{

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