[COMMITTERS] pgsql: Avoid bogus TwoPhaseState locking sequences

Avoid bogus TwoPhaseState locking sequences

The optimized code in 728bd991c3c4 contains a few invalid locking
sequences.  To wit, the original code would try to acquire an lwlock
that it already holds.  Avoid this by moving lock acquisitions to
higher-level code, and install appropriate assertions in low-level that
the correct mode is held.

Authors: Michael Paquier, Álvaro Herrera
Reported-By: chuanting wang
Bug: #14680
Discussion: https://postgr.es/m/20170531033228.1487.10124@wrigleys.postgresql.org

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/e90ceeaa495f5f40f224bcf84d2b0700eae8d7a3

Modified Files
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src/backend/access/transam/twophase.c | 87 +++++++++++++++++++----------------
src/backend/access/transam/xact.c     | 68 ++++++++++++++-------------
2 files changed, 83 insertions(+), 72 deletions(-)