I don't believe CPython should be working around a bug in specific Linux kernel versions in the standard library unless they are extremely pernicious and not considered to be a bug and thus ever be fixed in the OS kernel.

As the sendfile system call appears to infinitely return one of EAGAIN, EALREADY, EWOULDBLOCK, or EINPROGRESS in this case, there isn't anything CPython could do.  A retry/backoff loop won't help.

This should be worked around at the application level by whatever means are appropriate.