Default Can't set /data back to ro

I set /data to rw in order to make some changes.

Now, I'm trying to set it back to ro and I keep getting:
root@D6503:/ # mount -o ro,remount /dev/block/platform/msm_sdcc.1/by-name/userdata /data
latform/msm_sdcc.1/by-name/userdata /data <
mount: Device or resource busy
/data is used by all kinds of apps so I not sure how to make it not be busy. I tried doing ADB in recovery, but thats another issue. My device refuses to boot into recovery.
For Myself:
Sony Xperia Z2 D6503 Rooted with Stock Rom
N5100 Galaxy Note 8.0 (the one with a phone in it.) Rooted with Stock Rom

For the Wife:
Galaxy Note 3
Rooted with Stock Rom

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