For the context on this, please see Chris Siebenmann's blog entry on
Wandering Thoughts:

https://utcc.utoronto.ca/~cks/space/blog/linux/AlpineOverNFSFix

As of 2019-05-13, this has only been tested and verified on Ubuntu
18.04 LTS's standard 4.15.x server kernel. We have not tested it on
other kernels, and we don't know if the flock() behavior we're relying
on to fix the Alpine problem is guaranteed Linux NFS client behavior or
not.

See also:

https://utcc.utoronto.ca/~cks/space/blog/linux/KernelNFSPageBug
https://utcc.utoronto.ca/~cks/space/blog/tech/ExplicitSpecImportance

Chris Siebenmann, 2019-05-13