pgsql: Fix inplace update buffer self-deadlock.

Fix inplace update buffer self-deadlock.

A CacheInvalidateHeapTuple* callee might call
CatalogCacheInitializeCache(), which needs a relcache entry. Acquiring
a valid relcache entry might scan pg_class. Hence, to prevent
undetected LWLock self-deadlock, CacheInvalidateHeapTuple* callers must
not hold BUFFER_LOCK_EXCLUSIVE on buffers of pg_class. Move the
CacheInvalidateHeapTupleInplace() before the BUFFER_LOCK_EXCLUSIVE. No
back-patch, since I've reverted commit
243e9b40f1b2dd09d6e5bf91ebf6e822a2cd3704 from non-master branches.

Reported by Alexander Lakhin. Reviewed by Alexander Lakhin.

Discussion: https://postgr.es/m/10ec0bc3-5933-1189-6bb8-5dec4114558e@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0bada39c83a150079567a6e97b1a25a198f30ea3

Modified Files
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src/backend/access/heap/heapam.c | 21 +++++++++++++--------
src/backend/utils/cache/inval.c | 12 ++++++++++++
src/include/utils/inval.h | 1 +
3 files changed, 26 insertions(+), 8 deletions(-)