mv loses file permissions on some linux systems

[staticfloat]

Over the course of debugging JuliaLang/Pkg.jl#261, @KristofferC and I discovered that, on some Linux systems, moving a file from /tmp/ to a folder on the local filesystem loses permissions set on it, e.g. a file goes from 0775 to 0664. This seems to have some interaction with it being moved from one filesystem to another.

Example:

shell> mkdir /home/sabae/file_test

shell> mkdir /tmp/file_test

shell> cd /tmp/file_test
/tmp/file_test

shell> touch foo

shell> chmod +x foo

shell> ls -la
total 0
drwxr-xr-x   2 sabae sabae   60 Apr 25 14:17 .
drwxrwxrwt 198 root  root  4720 Apr 25 14:16 ..
-rwxr-xr-x   1 sabae sabae    0 Apr 25 14:17 foo

julia> mv("foo", "/home/sabae/file_test/foo")

shell> ls -la /home/sabae/file_test/
total 8
drwxr-xr-x  2 sabae sabae 4096 Apr 25 14:17 .
drwx------ 53 sabae sabae 4096 Apr 25 14:16 ..
-rw-r--r--  1 sabae sabae    0 Apr 25 14:17 foo

This is happening on the latest master:

Julia Version 0.7.0-DEV.4941
Commit 9f5351c36a (2018-04-24 14:26 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Xeon(R) CPU E3-1230 v6 @ 3.50GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, skylake)
Environment:

The relevant lines from mount:

$ mount
/dev/sda2 on / type ext4 (rw,relatime,data=ordered)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev)

[fredrikekre]

See also #20925

[KristofferC]

Anything that can be done to work around this?

[staticfloat]

Confirmed that #27295 fixes this.