xfs: remove the NULL fork handling in xfs_bmapi_read

Now that we fully verify the inode forks before they are added to the
inode cache, the crash reported in

  https://bugzilla.kernel.org/show_bug.cgi?id=204031

can't happen anymore, as we'll never let an inode that has inconsistent
nextents counts vs the presence of an in-core attr fork leak into the
inactivate code path.  So remove the work around to try to handle the
case, and just return an error and warn if the fork is not present.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_bmap.c

@@ -3891,7 +3891,8 @@ xfs_bmapi_read(
 	int			flags)
 {
 	struct xfs_mount	*mp = ip->i_mount;
-	struct xfs_ifork	*ifp;
+	int			whichfork = xfs_bmapi_whichfork(flags);
+	struct xfs_ifork	*ifp = XFS_IFORK_PTR(ip, whichfork);
 	struct xfs_bmbt_irec	got;
 	xfs_fileoff_t		obno;
 	xfs_fileoff_t		end;
@@ -3899,12 +3900,14 @@ xfs_bmapi_read(
 	int			error;
 	bool			eof = false;
 	int			n = 0;
-	int			whichfork = xfs_bmapi_whichfork(flags);
 
 	ASSERT(*nmap >= 1);
 	ASSERT(!(flags & ~(XFS_BMAPI_ATTRFORK | XFS_BMAPI_ENTIRE)));
 	ASSERT(xfs_isilocked(ip, XFS_ILOCK_SHARED|XFS_ILOCK_EXCL));
 
+	if (WARN_ON_ONCE(!ifp))
+		return -EFSCORRUPTED;
+
 	if (XFS_IS_CORRUPT(mp, !xfs_ifork_has_extents(ip, whichfork)) ||
 	    XFS_TEST_ERROR(false, mp, XFS_ERRTAG_BMAPIFORMAT)) {
 		return -EFSCORRUPTED;
@@ -3915,21 +3918,6 @@ xfs_bmapi_read(
 
 	XFS_STATS_INC(mp, xs_blk_mapr);
 
-	ifp = XFS_IFORK_PTR(ip, whichfork);
-	if (!ifp) {
-		/*
-		 * A missing attr ifork implies that the inode says we're in
-		 * extents or btree format but failed to pass the inode fork
-		 * verifier while trying to load it.  Treat that as a file
-		 * corruption too.
-		 */
-#ifdef DEBUG
-		xfs_alert(mp, "%s: inode %llu missing fork %d",
-				__func__, ip->i_ino, whichfork);
-#endif /* DEBUG */
-		return -EFSCORRUPTED;
-	}
-
 	if (!(ifp->if_flags & XFS_IFEXTENTS)) {
 		error = xfs_iread_extents(NULL, ip, whichfork);
 		if (error)