Rafał,

Am Montag, 22. Oktober 2018, 17:34:44 CEST schrieb Rafał Miłecki:
> Then I took a close look at ovl_copy_up_locked() and it seems above
> info isn't accurate. It seems to me that setxattr() happens between
> fsync and link. I modified my C app to follow that order (open, write,
> fsync, setxattr, link) and I can reproduce the problem now!
> 
> Steps to reproduce the problem:
> 1) compile tmptest.c
> 2) tmptest /overlay/upper/foo.txt user.bar baz
> 3) wait 5 seconds (so ubifs writes to flash)
> 4) power cut
> 5) boot again and check content of /overlay/upper/foo.txt
> 6) in my case content appears to be 00 00 00 00

Just returned from Edinburgh and had a chance to look at the problem.
The problem is not that no write-back happens, in fact it happens just fine.
But we have a problem upon journal replay if an unlinked file (O_TMPFILE)
gets relinked in combination with xattrs.

Can you please give the attached patch a try? It is not perfect but if I 
understand the problem correctly it should fix the issues you're facing.

Thanks,
//richard