fuse: fuse_flush must check mapping->flags for errors

fuse_flush() calls write_inode_now() that triggers writeback, but actual
writeback will happen later, on fuse_sync_writes(). If an error happens,
fuse_writepage_end() will set error bit in mapping->flags. So, we have to
check mapping->flags after fuse_sync_writes().

Signed-off-by: Maxim Patlasov <mpatlasov@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 4d99ff8f12 ("fuse: Turn writeback cache on")
Cc: <stable@vger.kernel.org> # v3.15+

fs/fuse/file.c

@@ -417,6 +417,15 @@ static int fuse_flush(struct file *file, fl_owner_t id)
 	fuse_sync_writes(inode);
 	inode_unlock(inode);
 
+	if (test_bit(AS_ENOSPC, &file->f_mapping->flags) &&
+	    test_and_clear_bit(AS_ENOSPC, &file->f_mapping->flags))
+		err = -ENOSPC;
+	if (test_bit(AS_EIO, &file->f_mapping->flags) &&
+	    test_and_clear_bit(AS_EIO, &file->f_mapping->flags))
+		err = -EIO;
+	if (err)
+		return err;
+
 	req = fuse_get_req_nofail_nopages(fc, file);
 	memset(&inarg, 0, sizeof(inarg));
 	inarg.fh = ff->fh;