Revert "nfs: clear SB_RDONLY before getting superblock"

This reverts commit 8cd9b78.

Silently ignoring the "ro" and "rw" mount options causes user confusion,
and regressions.

Reported-by: Alkis Georgopoulos<alkisg@gmail.com>
Cc: Li Lingfeng <lilingfeng3@huawei.com>
Fixes: 8cd9b78 ("nfs: clear SB_RDONLY before getting superblock")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: Trond Myklebust

fs/nfs/super.c

@@ -1308,17 +1308,8 @@ int nfs_get_tree_common(struct fs_context *fc)
 	if (IS_ERR(server))
 		return PTR_ERR(server);
 
-	/*
-	 * When NFS_MOUNT_UNSHARED is not set, NFS forces the sharing of a
-	 * superblock among each filesystem that mounts sub-directories
-	 * belonging to a single exported root path.
-	 * To prevent interference between different filesystems, the
-	 * SB_RDONLY flag should be removed from the superblock.
-	 */
 	if (server->flags & NFS_MOUNT_UNSHARED)
 		compare_super = NULL;
-	else
-		fc->sb_flags &= ~SB_RDONLY;
 
 	/* -o noac implies -o sync */
 	if (server->flags & NFS_MOUNT_NOAC)