CIFS server / filesystem that worked fine in Ubuntu 20.04 breaks in Ubuntu 20.10

[Jonathan Kamens]

After upgrading from 20.04 to 20.10 yesterday, my backup overnight failed. rclone reported these errors trying to read from the CIFS filesystem being backed up:

2020/10/26 18:45:00 ERROR : 2006/0713: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:45:00 ERROR : 2019/0417: error reading source directory: directory not found
2020/10/26 18:45:01 ERROR : 2018/0518: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:45:02 ERROR : 2018/1112: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:45:03 ERROR : [private path one elided]/2017-08-29: error reading source directory: failed to read directory entry: readdirent: interrupted system call
2020/10/26 18:45:04 ERROR : [private path one elided]/2018-07-22: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:45:04 ERROR : [private path one elided]/Hangouts/[private path two elided]: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:45:11 ERROR : Encrypted drive 'B2-encrypted:pictures': not deleting files as there were IO errors
2020/10/26 18:45:11 ERROR : Encrypted drive 'B2-encrypted:pictures': not deleting directories as there were IO errors
2020/10/26 18:45:11 ERROR : Attempt 1/3 failed with 8 errors and: march failed with 7 error(s): first error: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:46:20 ERROR : 2016/1229: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:46:21 ERROR : [private path one elided]/2017-12-31 - 2018-01-01: error reading source directory: failed to read directory entry: readdirent: interrupted system call
2020/10/26 18:46:22 ERROR : [private path one elided]/2018-03-19: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:46:22 ERROR : [private path one elided]/2018-07-19: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:46:27 ERROR : [private path one elided]/backup/Screenshots: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:46:27 ERROR : Encrypted drive 'B2-encrypted:pictures': not deleting files as there were IO errors
2020/10/26 18:46:27 ERROR : Encrypted drive 'B2-encrypted:pictures': not deleting directories as there were IO errors
2020/10/26 18:46:27 ERROR : Attempt 2/3 failed with 6 errors and: march failed with 5 error(s): first error: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:47:32 ERROR : [private path one elided]: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:47:33 ERROR : 2014/0606: error reading source directory: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:47:36 ERROR : Encrypted drive 'B2-encrypted:pictures': not deleting files as there were IO errors
2020/10/26 18:47:36 ERROR : Encrypted drive 'B2-encrypted:pictures': not deleting directories as there were IO errors
2020/10/26 18:47:36 ERROR : Attempt 3/3 failed with 3 errors and: march failed with 2 error(s): first error: failed to read directory entry: readdirent: no such file or directory
2020/10/26 18:47:36 Failed to sync with 3 errors: last error was: march failed with 2 error(s): first error: failed to read directory entry: readdirent: no such file or directory

In addition I see the following in dmesg:

[ 371.203517] CIFS: VFS: \\[private LAN host name elided]\photo Close interrupted close
[ 373.131953] CIFS: VFS: \\[private LAN host name elided]\photo Close interrupted close
[ 374.421419] CIFS: VFS: \\[private LAN host name elided]\photo Close interrupted close

I want to emphasize that this worked fine in 20.04 basically forever, and then stopped working immediately after upgrading to 20.10. I tried rebooting, didn't help.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: linux-image-5.8.0-25-generic 5.8.0-25.26
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Mon Oct 26 18:51:48 2020
InstallationDate: Installed on 2019-01-02 (663 days ago)
InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.3)
MachineType: Acer Predator G6-710
ProcFB:

ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.8.0-25-generic root=/dev/mapper/ubuntu--vg-root ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-5.8.0-25-generic N/A
 linux-backports-modules-5.8.0-25-generic N/A
 linux-firmware 1.190
SourcePackage: linux
UpgradeStatus: Upgraded to groovy on 2020-10-25 (1 days ago)
dmi.bios.date: 05/18/2016
dmi.bios.release: 5.11
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: R01-A4
dmi.board.name: Predator G6-710
dmi.board.vendor: Acer
dmi.chassis.type: 3
dmi.chassis.vendor: Acer
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrR01-A4:bd05/18/2016:br5.11:svnAcer:pnPredatorG6-710:pvr:rvnAcer:rnPredatorG6-710:rvr:cvnAcer:ct3:cvr:
dmi.product.family: Acer Desktop
dmi.product.name: Predator G6-710
dmi.sys.vendor: Acer
modified.conffile..etc.apport.crashdb.conf: [modified]
mtime.conffile..etc.apport.crashdb.conf: 2020-04-17T14:48:03.262066

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This change was made by a bot.