OpenZFS 9690 - metaslab of vdev with no space maps was flushed during removal

[behlendorf]

Motivation and Context

OpenZFS-issue: https://www.illumos.org/issues/9690
OpenZFS-commit: openzfs/openzfs@4e75ba6826

Description

This seems to point to that the space map's dnode has been freed probably through dnode_sync_free() as this is the function that actually frees the dnode and zeroes out all the above fields.

The failure occurs while we were trying to flush a metaslab in spa_sync() and these code paths have assertions everywhere that we only flush metaslabs that have a space map (e.g. went through metaslab_sync() at least once since the creation of the pool). There is a contradiction then where the metaslab's spacemap information in memory (ms_sm data) exist but the actual space map on-disk have been freed.

To fix this, we first want to try calling vdev_remove_empty() only for log devices in vdev_sync().

How Has This Been Tested?

Locally built, merged to illumos, pending CI results.

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.

[gmelikov]

Lgtm

[codecov]

Codecov Report

Merging #8039 into master will decrease coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #8039      +/-   ##
==========================================
- Coverage   78.46%   78.35%   -0.12%     
==========================================
  Files         377      377              
  Lines      114404   114405       +1     
==========================================
- Hits        89768    89639     -129     
- Misses      24636    24766     +130

Flag	Coverage Δ
#kernel	78.72% <100%> (-0.01%)	⬇️
#user	66.83% <14.28%> (-0.74%)	⬇️

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