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Commit19f8232

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Fix ReadRecentBuffer for local buffers.
It incorrectly used GetBufferDescriptor instead ofGetLocalBufferDescriptor, causing it to not find the correct buffer inmost cases, and performing an out-of-bounds memory read in the cornercase that temp_buffers > shared_buffers.It also bumped the usage-count on the buffer, even if it waspreviously pinned. That won't lead to crashes or incorrect results,but it's different from what the shared-buffer case does, anddifferent from the usual code in LocalBufferAlloc. Fix that too, andmake the code ordering match LocalBufferAlloc() more closely, so thatit's easier to verify that it's doing the same thing.Currently, ReadRecentBuffer() is only used with non-temp relations, inWAL redo, so the broken code is currently dead code. However, it couldbe used by extensions.Backpatch-through: 14Discussion:https://www.postgresql.org/message-id/2d74b46f-27c9-fb31-7f99-327a87184cc0%40iki.fiReviewed-by: Thomas Munro, Zhang Mingli, Richard Guo
1 parentbd6cfbf commit19f8232

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‎src/backend/storage/buffer/bufmgr.c

Lines changed: 16 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -636,18 +636,28 @@ ReadRecentBuffer(RelFileNode rnode, ForkNumber forkNum, BlockNumber blockNum,
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637637
if (BufferIsLocal(recent_buffer))
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{
639-
bufHdr=GetBufferDescriptor(-recent_buffer-1);
639+
intb=-recent_buffer-1;
640+
641+
bufHdr=GetLocalBufferDescriptor(b);
640642
buf_state=pg_atomic_read_u32(&bufHdr->state);
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642644
/* Is it still valid and holding the right tag? */
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if ((buf_state&BM_VALID)&&BUFFERTAGS_EQUAL(tag,bufHdr->tag))
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{
645-
/* Bump local buffer's ref and usage counts. */
647+
/*
648+
* Bump buffer's ref and usage counts. This is equivalent of
649+
* PinBuffer for a shared buffer.
650+
*/
651+
if (LocalRefCount[b]==0)
652+
{
653+
if (BUF_STATE_GET_USAGECOUNT(buf_state)<BM_MAX_USAGE_COUNT)
654+
{
655+
buf_state+=BUF_USAGECOUNT_ONE;
656+
pg_atomic_unlocked_write_u32(&bufHdr->state,buf_state);
657+
}
658+
}
659+
LocalRefCount[b]++;
646660
ResourceOwnerRememberBuffer(CurrentResourceOwner,recent_buffer);
647-
LocalRefCount[-recent_buffer-1]++;
648-
if (BUF_STATE_GET_USAGECOUNT(buf_state)<BM_MAX_USAGE_COUNT)
649-
pg_atomic_write_u32(&bufHdr->state,
650-
buf_state+BUF_USAGECOUNT_ONE);
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652662
pgBufferUsage.local_blks_hit++;
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