Author:     Noah Misch <noah@leadboat.com>
Commit:     Noah Misch <noah@leadboat.com>

    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.
    Commit 243e9b40f1b2dd09d6e5bf91ebf6e822a2cd3704 introduced this
    regression.  No back-patch, since I've reverted the culprit from
    non-master branches.
    
    Reported by Alexander Lakhin.  Reviewed by FIXME.
    
    Discussion: https://postgr.es/m/10ec0bc3-5933-1189-6bb8-5dec4114558e@gmail.com

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 1748eaf..9a31cdc 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -6214,6 +6214,17 @@ heap_inplace_lock(Relation relation,
 
 	Assert(BufferIsValid(buffer));
 
+	/*
+	 * Construct shared cache inval if necessary.  Because we pass a tuple
+	 * version without our own inplace changes or inplace changes other
+	 * sessions complete while we wait for locks, inplace update mustn't
+	 * change catcache lookup keys.  But we aren't bothering with index
+	 * updates either, so that's true a fortiori.  After LockBuffer(), it
+	 * would be too late, because this might reach a
+	 * CatalogCacheInitializeCache() that locks "buffer".
+	 */
+	CacheInvalidateHeapTupleInplace(relation, oldtup_ptr, NULL);
+
 	LockTuple(relation, &oldtup.t_self, InplaceUpdateTupleLock);
 	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
 
@@ -6309,6 +6320,7 @@ heap_inplace_lock(Relation relation,
 	if (!ret)
 	{
 		UnlockTuple(relation, &oldtup.t_self, InplaceUpdateTupleLock);
+		ForgetInplace_Inval();
 		InvalidateCatalogSnapshot();
 	}
 	return ret;
@@ -6345,14 +6357,6 @@ heap_inplace_update_and_unlock(Relation relation,
 	dst = (char *) htup + htup->t_hoff;
 	src = (char *) tuple->t_data + tuple->t_data->t_hoff;
 
-	/*
-	 * Construct shared cache inval if necessary.  Note that because we only
-	 * pass the new version of the tuple, this mustn't be used for any
-	 * operations that could change catcache lookup keys.  But we aren't
-	 * bothering with index updates either, so that's true a fortiori.
-	 */
-	CacheInvalidateHeapTupleInplace(relation, tuple, NULL);
-
 	/* Like RecordTransactionCommit(), log only if needed */
 	if (XLogStandbyInfoActive())
 		nmsgs = inplaceGetInvalidationMessages(&invalMessages,
@@ -6481,6 +6485,7 @@ heap_inplace_unlock(Relation relation,
 {
 	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
 	UnlockTuple(relation, &oldtup->t_self, InplaceUpdateTupleLock);
+	ForgetInplace_Inval();
 }
 
 #define		FRM_NOOP				0x0001
diff --git a/src/backend/utils/cache/inval.c b/src/backend/utils/cache/inval.c
index 986850c..fc972ed 100644
--- a/src/backend/utils/cache/inval.c
+++ b/src/backend/utils/cache/inval.c
@@ -1202,6 +1202,18 @@ AtInplace_Inval(void)
 }
 
 /*
+ * ForgetInplace_Inval
+ *		Alternative to PreInplace_Inval()+AtInplace_Inval(): discard queued-up
+ *		invalidations.  This lets inplace update enumerate invalidations
+ *		optimistically, before locking the buffer.
+ */
+void
+ForgetInplace_Inval(void)
+{
+	inplaceInvalInfo = NULL;
+}
+
+/*
  * AtEOSubXact_Inval
  *		Process queued-up invalidation messages at end of subtransaction.
  *
diff --git a/src/include/utils/inval.h b/src/include/utils/inval.h
index 3390e7a..299cd75 100644
--- a/src/include/utils/inval.h
+++ b/src/include/utils/inval.h
@@ -30,6 +30,7 @@ extern void AtEOXact_Inval(bool isCommit);
 
 extern void PreInplace_Inval(void);
 extern void AtInplace_Inval(void);
+extern void ForgetInplace_Inval(void);
 
 extern void AtEOSubXact_Inval(bool isCommit);