Fix instance of elog() called while holding a spinlock

This broke the project rule to not call any complex code while a spinlock is held. Issue introduced by b89e151. Discussion: https://postgr.es/m/[email protected] Back-through: 9.5

Author: michaelpq

src/backend/replication/logical/logical.c

@@ -972,25 +972,33 @@ LogicalIncreaseRestartDecodingForSlot(XLogRecPtr current_lsn, XLogRecPtr restart
 {
 slot->candidate_restart_valid = current_lsn;
 slot->candidate_restart_lsn = restart_lsn;
+SpinLockRelease(&slot->mutex);
 
 elog(DEBUG1, "got new restart lsn %X/%X at %X/%X",
 (uint32) (restart_lsn >> 32), (uint32) restart_lsn,
 (uint32) (current_lsn >> 32), (uint32) current_lsn);
 }
 else
 {
+XLogRecPtr	candidate_restart_lsn;
+XLogRecPtr	candidate_restart_valid;
+XLogRecPtr	confirmed_flush;
+
+candidate_restart_lsn = slot->candidate_restart_lsn;
+candidate_restart_valid = slot->candidate_restart_valid;
+confirmed_flush = slot->data.confirmed_flush;
+SpinLockRelease(&slot->mutex);
+
 elog(DEBUG1, "failed to increase restart lsn: proposed %X/%X, after %X/%X, current candidate %X/%X, current after %X/%X, flushed up to %X/%X",
 (uint32) (restart_lsn >> 32), (uint32) restart_lsn,
 (uint32) (current_lsn >> 32), (uint32) current_lsn,
-(uint32) (slot->candidate_restart_lsn >> 32),
-(uint32) slot->candidate_restart_lsn,
-(uint32) (slot->candidate_restart_valid >> 32),
-(uint32) slot->candidate_restart_valid,
-(uint32) (slot->data.confirmed_flush >> 32),
-(uint32) slot->data.confirmed_flush
-);
+(uint32) (candidate_restart_lsn >> 32),
+(uint32) candidate_restart_lsn,
+(uint32) (candidate_restart_valid >> 32),
+(uint32) candidate_restart_valid,
+(uint32) (confirmed_flush >> 32),
+(uint32) confirmed_flush);
 }
-SpinLockRelease(&slot->mutex);
 
 /* candidates are already valid with the current flush position, apply */
 if (updated_lsn)