(cloudberry) 04/50: Don't release index root page pin in ginFindParents().

[le...@apache.org]

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leborchuk pushed a commit to branch REL_2_STABLE
in repository https://gitbox.apache.org/repos/asf/cloudberry.git

commit 306025e0a81e7e993b196ba40cff864e21a6f936
Author: Tom Lane <tg...@sss.pgh.pa.us>
AuthorDate: Mon Nov 13 11:44:35 2023 -0500

    Don't release index root page pin in ginFindParents().
    
    It's clearly stated in the comments that ginFindParents() must keep
    the pin on the index's root page that's associated with the topmost
    GinBtreeStack item.  However, the code path for the case that the
    desired downlink has been pushed down to the next index level
    ignored this proviso, and would release the pin anyway if we were
    still examining the root level.  That led to an assertion failure
    or "buffer NNNN is not owned by resource owner" error later, when
    we try to release the pin again at the end of the insertion.
    
    This is quite hard to reproduce, since it can only happen if an
    index root page split occurs concurrently with our own insertion.
    Thanks to Jeff Janes for finding a test case that triggers it
    often enough to allow investigation.
    
    This has been there since the beginning of GIN, so back-patch
    to all supported branches.
    
    Discussion: https://postgr.es/m/CAMkU=1yCAKtv86dMrD__Ja-7KzjE=uMeKX8y__cx5W-OEWy2ow@mail.gmail.com
    (cherry picked from commit d900e74e054816cfa94d99a272e174baa7608716)
---
 src/backend/access/gin/ginbtree.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/backend/access/gin/ginbtree.c b/src/backend/access/gin/ginbtree.c
index 482cf10877c..4fb9aa6f257 100644
--- a/src/backend/access/gin/ginbtree.c
+++ b/src/backend/access/gin/ginbtree.c
@@ -274,7 +274,11 @@ ginFindParents(GinBtree btree, GinBtreeStack *stack)
 			blkno = GinPageGetOpaque(page)->rightlink;
 			if (blkno == InvalidBlockNumber)
 			{
-				UnlockReleaseBuffer(buffer);
+				/* Link not present in this level */
+				LockBuffer(buffer, GIN_UNLOCK);
+				/* Do not release pin on the root buffer */
+				if (buffer != root->buffer)
+					ReleaseBuffer(buffer);
 				break;
 			}
 			buffer = ginStepRight(buffer, btree->index, GIN_EXCLUSIVE);


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