overlayfs: propagate errors from upper to overlay sb in sync_fs

Peek at the upper layer's errseq_t at mount time for volatile mounts,
and record it in the per-sb info. In sync_fs, check for an error since
the recorded point and set it in the overlayfs superblock if there was
one.

Signed-off-by: Jeff Layton <jlayton@kernel.org>

fs/overlayfs/ovl_entry.h

@@ -81,6 +81,7 @@ struct ovl_fs {
 	atomic_long_t last_ino;
 	/* Whiteout dentry cache */
 	struct dentry *whiteout;
+	errseq_t err_mark;
 };
 
 static inline struct vfsmount *ovl_upper_mnt(struct ovl_fs *ofs)

fs/overlayfs/super.c

@@ -267,8 +267,13 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
 	if (!ovl_upper_mnt(ofs))
 		return 0;
 
-	if (!ovl_should_sync(ofs))
-		return 0;
+	if (!ovl_should_sync(ofs)) {
+		/* Propagate errors from upper to overlayfs */
+		ret = errseq_check(&upper_sb->s_wb_err, ofs->err_mark);
+		errseq_set(&sb->s_wb_err, ret);
+		return ret;
+	}
+
 	/*
 	 * Not called for sync(2) call or an emergency sync (SB_I_SKIP_SYNC).
 	 * All the super blocks will be iterated, including upper_sb.
@@ -2007,8 +2012,11 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 		sb->s_stack_depth = ovl_upper_mnt(ofs)->mnt_sb->s_stack_depth;
 		sb->s_time_gran = ovl_upper_mnt(ofs)->mnt_sb->s_time_gran;
-
 	}
+
+	if (ofs->config.ovl_volatile)
+		ofs->err_mark = errseq_peek(&ovl_upper_mnt(ofs)->mnt_sb->s_wb_err);
+
 	oe = ovl_get_lowerstack(sb, splitlower, numlower, ofs, layers);
 	err = PTR_ERR(oe);
 	if (IS_ERR(oe))