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fix(kubernetes): keep NFS publish from hanging on a dead server - #4791
Aleksei Sviridkin (lexfrei) wants to merge 1 commit into
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title clearly and concisely describes the main change: preventing NFS publish operations from hanging when the server is unavailable. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
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Actionable comments posted: 1
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only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @packages/apps/kubernetes/images/kubevirt-csi-driver/node.go:
- Line 116: In the node publish migration flow, handle errors from os.Stat(dst)
explicitly: continue to os.Rename(src, dst) only when the destination is absent,
and fail publishing for every other stat error. Add a test covering a
non-NotExist stat error and confirming the rename is not attempted; leave the
rootOpts mount settings unchanged.
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packages/apps/kubernetes/images/kubevirt-csi-driver/node.gopackages/apps/kubernetes/images/kubevirt-csi-driver/node_test.go
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Verdict
LGTM
The three bounded-NFS changes hang together. The concurrency guard matches the CSI contract: Aborted is the right code for a pending op, and kubelet treats it as non-final and retries with backoff. No return path leaks the guard entry, and each new behaviour is pinned by a test that goes red once you revert it. CI on the head is green, and the change still passes after current main is merged in, both the Go suite and the kubernetes chart unittests. Everything below is non-blocking.
Findings
- [MINOR]
packages/apps/kubernetes/images/kubevirt-csi-driver/node.go:153, Stat to Lstat silently strands a legacy root file that collides with a /data symlink
- [NIT]
packages/apps/kubernetes/images/kubevirt-csi-driver/node.go:26, Package-level var lstat is a test seam that becomes a data race under t.Parallel
- [NIT]
packages/apps/kubernetes/images/kubevirt-csi-driver/node.go:134, MkdirAll on the soft temp mount can report a misleading EEXIST, and the error omits the volume id
Notes
- The final
/datamount stays hard with the default foreground retry (~2m) on a dead server. That is bounded and within kubelet's 2m deadline, and the per-target guard keeps retries from piling up, so it is not an indefinite hang. The residual hang cases (TCP up / service hung, a target already hard-mounted, publish/unpublish not coordinated) are scoped out and tracked in #4814. No change requested. - Hermetic review. The image was not rebuilt and not run against a live or dead NFS server; the CSI-level behaviour was reasoned and unit-verified against the fake mounter only. If you want it exercised on a cluster,
cozystack-pr-testcan drive it on a dev cluster.
Findings not anchored to changed lines
These reference code outside this PR's diff (unchanged files, or lines outside a hunk), so GitHub cannot render them inline.
[NIT] packages/apps/kubernetes/images/kubevirt-csi-driver/node.go:134 MkdirAll on the soft temp mount can report a misleading EEXIST, and the error omits the volume id
Now that the temp root is soft, os.MkdirAll(dataDir, 0777) is reachable with the server unreachable: Stat(dataDir) returns EIO, MkdirAll walks up to the already-existing local temp dir, Mkdir returns EEXIST, and the confirming Lstat on the mountpoint EIOs, so MkdirAll surfaces mkdir /tmp/nfs-init-...: file exists on exactly the dead-server failure this PR targets. The node operator then reads a temp-dir-already-exists message for what is really a dead server. os.Mkdir plus errors.Is(err, fs.ErrExist) would surface the real errno. Minor and cosmetic, but note this error (and its temp-mount siblings at node.go:100 and node.go:124) also omit the volume %s that the migration errors at node.go:141/156/163 carry, worth making the publish errors uniformly greppable by volume.
| // Lstat: a user's symlink in /data counts as present whatever it | ||
| // points at, and is not replaced. | ||
| if _, err := lstat(dst); err == nil { | ||
| continue // already exists in /data, skip |
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[MINOR] Stat to Lstat silently strands a legacy root file that collides with a /data symlink
The switch from os.Stat to lstat on the migration destination is deliberate and tested, and it does the right thing for the dangling/looping-symlink case coderabbit raised. One corner changes behaviour with no trace left: if the export root holds a legacy file f and /data already holds a symlink named f, lstat now reports the symlink as present and continue skips the migration, so f stays in the export root, which the pod never mounts. Before this change os.Stat followed a dangling symlink, hit ENOENT, and the rename moved f into /data. No data is lost (the file is still in the export root, recoverable by an admin), and the corner needs the export root written outside the pod, so it is narrow. The gap is diagnosability: this skip has no log, while the comment at node.go:138 promises the publish fails rather than hide user data. A klog.Warningf naming the volume and the skipped entry would let an operator find a stranded file. Please confirm skip-and-leave is intended over migrate-and-replace.
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Yes, skipping is intended: the migration never replaces anything in /data, a symlink included. It was silent though. f76dedf logs a warning with the volume and the entry left in the export root, and a test pins it.
| var _ csi.NodeServer = &WrappedNodeService{} | ||
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| // lstat is replaced in tests: the soft temp mount's EIO cannot be produced locally. | ||
| var lstat = os.Lstat |
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[NIT] Package-level var lstat is a test seam that becomes a data race under t.Parallel
var lstat = os.Lstat is swapped by a test. It is safe today (no test in the package calls t.Parallel, and the swapper uses t.Setenv, which panics under Parallel), but it is a shared mutable global read on the server's publish path, so it turns into a data race the moment any test that reaches the migration loop is marked parallel. Making it a field on WrappedNodeService defaulted to os.Lstat in main.go removes the global without changing the seam.
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Fixed in f76dedf. lstat is a field on WrappedNodeService now, nil means os.Lstat, so main.go doesn't change. mkdir got the same treatment for the MkdirAll note.
The kubevirt-csi node plugin mounts the NFS export root into a temp dir to create /data and migrate old files. That mount was hard, so with the server gone the mkdir, readdir and rename calls on it never returned. kubelet gives up after 2m and retries, and every retry blocked the same way, piling up goroutines and nfs-init-* dirs. Mount the temp root soft, so its RPCs fail once the connection to the server is declared dead instead of blocking forever; it only does metadata work that a retried publish redoes. retry=0 keeps mount.nfs from retrying a failed temp mount for 2m. timeo and retrans keep their defaults, because the first mount of a server sets them for the connection the pods' mounts of it share. The volume mount the pod gets stays hard, since a soft mount can report a failed write the server applied. Over NFSv4 that soft failure takes minutes, and a stat of a target that is already hard-mounted can block for good, so a publish for a target path that already has one running now returns Aborted instead of starting another. A soft stat can fail with EIO on a file /data already holds, and a rename issued once the server is back would replace it, so the migration now fails the publish on any stat error other than a missing destination. It checks the destination with lstat, so a user's symlink in /data that loops or dangles counts as present instead of failing every publish or being replaced by the rename. The skip it makes for a destination already in /data leaves the root entry where the pod cannot see it, so it is now logged as a warning. /data is created with a plain mkdir, since with the server gone MkdirAll fails its stat on the mount point and then reports the local temp dir as already existing instead of the EIO. The temp mount errors now name the volume, like the migration errors do. Assisted-by: LLM Signed-off-by: Aleksei Sviridkin <[email protected]>
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IvanHunters f76dedf takes all three notes. For the out-of-diff one, /data is created with a plain mkdir now, so a dead server reports EIO instead of "file exists", and the temp mount errors name the volume. The push dropped your approval, could you take another look? |
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Verdict
LGTM
The push closes all three notes from the earlier round. Every fix carries a test that goes back to red once you revert it, the branch still passes after a merge of current main, and the head is green in CI.
Checked and correct
The migration skip now logs the volume and the entry it leaves in the export root, and a stat that fails for anything other than "not found" fails the publish rather than renaming over what it could not see (node.go:165, node.go:167). The test seam moved off a package-level var onto nil-defaulted struct fields (node.go:38), so nothing shared and mutable sits on the publish path anymore. WrappedNodeService is only ever taken by pointer, so its sync.Map never gets copied, and -race stays clean on the concurrency tests. /data is created with a plain os.Mkdir now, so a dead server surfaces its EIO instead of a masked "already exists"; the fs.ErrExist case stays the no-op it always was, and the temp-mount and temp-dir errors name the volume (node.go:145).
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What this PR does
When the kubevirt-csi node plugin publishes an NFS volume, it first mounts the export root into an
nfs-init-*temp dir to create/dataand move old files into it. That temp mount was hard. If the NFS server stopped answering at that point, the publish call never returned. kubelet gives up after 2m and retries, each retry blocked the same way, and goroutines and temp dirs piled up until the server came back or the plugin restarted.The fix does three things:
softwithretry=0. It only does metadata work that a retried publish redoes, so an error there is harmless, and a stuck call now ends on its own once the connection to the server is declared dead. The mount the pod gets stays hard, because a soft mount can report a failed write that the server did apply.Abortedinstead of starting another. This is what stops the pile-up: at most one call per target path is stuck at a time./datanow checks the destination withlstatand fails the publish on any error other than a missing file. With the soft mount, the check can fail with EIO on a file that/dataalready holds, and a rename issued after the server comes back would replace that file.lstatkeeps a user's symlink in/datathat loops or dangles from failing every publish. Such a symlink counts as present and is left alone, while before this change the rename replaced a dangling one.I kept the default retry timeouts on purpose, although the issue suggested lowering
timeoandretrans. The Linux client shares one connection per server for all of that server's mounts on the node, and the first mount sets the connection's TCP timeouts. Lowering them on the temp mount would have changed the timeouts of the pods' hard mounts too. Over NFSv4, a soft RPC fails only after the connection is declared dead, so a stuck call takes minutes to end, longer than kubelet's 2m deadline. The guard keeps kubelet's retries from adding new calls during that time.The guard works per target path, not per volume. Two pods on one node that use the same RWX volume still publish in parallel, and each pod can have at most one stuck call.
The unit tests pin the mount options on both mounts, the guard behaviour including its release after a failed publish, and the destination check: a failed check stops the move, and a symlink in
/datastays in place. They use the fake mounter. I did not test against a real NFS server that went away.Not covered here, and tracked in #4814:
Mountfrom mount-utils runsmountwith no deadline. This predates this change, and the guard bounds it the same way.umount.nfsafter a timeout, and a possiblestatbeforeumount2. Both may end sooner now that the temp mount is soft, but I have not verified either.Refs #4581
Screenshots
Not a UI change.
Downstream repositories
The change is limited to the kubevirt-csi node plugin's Go code. None of the triggers in the contributing guide's map apply: no package added or renamed, no platform values, variants, release assets, ApplicationDefinition semantics or developer tooling touched.
Release note
Summary by CodeRabbit
Abortederror. Different targets remain available, and a target can be used again after a request finishes, including after a failed attempt.