[FS#4100] SQUASHFS errors with OpenWrt 21.02

[OpenWrt Bugs]

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A new Flyspray task has been opened.  Details are below. 

User who did this - crowston (crowston) 

Attached to Project - OpenWrt/LEDE Project
Summary - SQUASHFS errors with OpenWrt 21.02
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - Supply the following if possible:
 - Device problem occurs on

Western Digital My Net N750

 - Software versions of OpenWrt/LEDE release, packages, etc.

openwrt-21.02.0 

strongswan, dnscrypt-proxy2, avahi-utils, luci-app-ddns

 - Steps to reproduce

I installed openwrt-21.02.0-ath79-generic-wd_mynet-n750-squashfs-sysupgrade.bin on a Western Digital My Net N750 that had been running openwrt-19. 

The router seemed okay initially but after power cycling, it started reporting errors:

Oct 17 12:20:37 router2 kernel: [   38.613970] SQUASHFS error: xz decompression failed, data probably corrupt
Oct 17 12:20:37 router2 kernel: [   38.621029] SQUASHFS error: squashfs_read_data failed to read block 0x23686e
Oct 17 12:20:37 router2 kernel: [   38.628199] SQUASHFS error: Unable to read fragment cache entry [23686e]
Oct 17 12:20:37 router2 kernel: [   38.635010] SQUASHFS error: Unable to read page, block 23686e, size 16b28

The filesystem problem would leave some random file damaged, so different services would fail. Over time, the router became less and less functional as various files became inaccessible and after a few cycles, wouldn't boot at all. 

I wondered if there was a problem with my old configuration on the new release (though I'm not sure how that could damage the squashfs), so I reinstalled a few more times in different ways, e.g., doing a factory install (openwrt-21.02.0-ath79-generic-wd_mynet-n750-squashfs-factory.bin and then the upgrade) instead of just the upgrade, and configuring from scratch rather than from the backup. But each time I had the same problem with the router.  

It wasn't the same block on different installs, I noticed, but it seemed to be consistent for a particular installation attempt. 

Oct 17 16:11:14 router2 kernel: [   53.182571] SQUASHFS error: xz decompression failed, data probably corrupt
Oct 17 16:11:14 router2 kernel: [   53.189582] SQUASHFS error: squashfs_read_data failed to read block 0x21e9e6
Oct 17 16:11:14 router2 kernel: [   53.196749] SQUASHFS error: Unable to read fragment cache entry [21e9e6]
Oct 17 16:11:14 router2 kernel: [   53.203559] SQUASHFS error: Unable to read page, block 21e9e6, size fd9c

Once there were two blocks (I think this is a reboot of the install above):

Oct 17 16:29:04 router2 kernel: [   78.505075] SQUASHFS error: xz decompression failed, data probably corrupt
Oct 17 16:29:04 router2 kernel: [   78.512103] SQUASHFS error: squashfs_read_data failed to read block 0x1e6e76
Oct 17 16:29:05 router2 kernel: [   79.111366] SQUASHFS error: xz decompression failed, data probably corrupt
Oct 17 16:29:05 router2 kernel: [   79.118386] SQUASHFS error: squashfs_read_data failed to read block 0x21e9e6
Oct 17 16:29:05 router2 kernel: [   79.125565] SQUASHFS error: Unable to read fragment cache entry [21e9e6]
Oct 17 16:29:05 router2 kernel: [   79.132445] SQUASHFS error: Unable to read page, block 21e9e6, size fd9c

One time there was first a jffs error, followed by lots of squashfs errors. Sorry, I don't have the log for that one. 

I now realize that I should have tried power cycling a clean install a few times to see if there were errors right away or if they only happened after files were installed/changed. 

To check whether the router was just having a hardware problem, I reinstalled openwrt-19.07.8 and configured it the same. I have not seen any errors after a few power cycles, which points to a problem with the new release. I did not see any bug reports on this tracker that mention squashfs problems and googling, I did not find any useful discussions, hence this bug report. 

I guess it could be that the new release uses a bad bit of memory that the earlier release managed to miss. I looked for but didn't find a memory test utility, so I don't know how to examine that possibility. Though the fact that it was different blocks each time makes it not sound like a hardware problem. 

More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=4100

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