for-linus-rseq

of TIF_NOTIFY_RESUME, e.g. for task migration, clears the flag without
informing rseq and leads to stale data in userspace's rseq struct.

I'm sending this as a separate pull request since it's not code
that I usually touch.  In particular, patch 2 ("entry: rseq: Call
rseq_handle_notify_resume() in tracehook_notify_resume()") is just a
cleanup to try and make future bugs less likely.  If you prefer this to
be sent via Thomas and only in 5.16, please speak up.