ZTS: fix spurious failures in mv_files

[chrisrd]

Fix spurious failures in mv_files.

Description

The test could fail because of a race condition between the files being generated in the background and attempting to move the files. Wait for all file generation to complete before trying to move the files around.

Also, clean up the waiting: the 'wait' command without arguments waits for all child pids. There's no need to imperfectly look to see if each pid exists and then wait for that pid explicitly. (Imperfectly: no need to look at all pids on the system with -e, just our own pids would have been fine, and looking for pid 123 with grep would find 1234 thus negating the purpose of the check).

Note: the leading whitespace in this file is atrocious, but fixing it all hides what's being fixed.

Motivation and Context

Spurious failures are annoying and time wasting.

How Has This Been Tested?

Run zfs-tests

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.
• Change has been approved by a ZFS on Linux member.

[gmelikov]

LGTM, thanks, great find!

[codecov]

Codecov Report

Merging #7258 into master will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7258      +/-   ##
==========================================
- Coverage   76.57%   76.42%   -0.16%     
==========================================
  Files         327      327              
  Lines      103866   103866              
==========================================
- Hits        79537    79380     -157     
- Misses      24329    24486     +157

Flag	Coverage Δ
#kernel	76.18% <ø> (-0.21%)	⬇️
#user	65.7% <ø> (-0.22%)	⬇️

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[chrisrd]

Worth mentioning: I checked for similar faulty idioms in the rest of tests and didn't find any...

Look for cut/pasted code:

$ grep -riI 'GANGPIDS' tests || grep none
none

Manually inspect for backgrounding without waiting:

$ pat='[^&]&[[:space:]]*$'; vi +/"$pat" $(grep -rlI "$pat" tests)

[behlendorf]

Thanks!