pgsql: Fix VM buffer pin management in heap_lock_updated_tuple_rec().

Fix VM buffer pin management in heap_lock_updated_tuple_rec().

Sloppy coding in this function could lead to leaking a VM buffer pin,
or to attempting to free the same pin twice.  Repair.  While at it,
reduce the code's tendency to free and reacquire the same page pin.

Back-patch to 9.6; before that, this routine did not concern itself
with VM pages.

Amit Kapila and Tom Lane

Discussion: https://postgr.es/m/CAA4eK1KJKwhc=isgTQHjM76CAdVswzNeAuZkh_cx-6QgGkSEgA@mail.gmail.com

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/96d2df840b0669aad6792b459805367ba70641af

Modified Files
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src/backend/access/heap/heapam.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)