Linux 5.12-rc2 Likely Coming Early Due To That Nasty File-System Corruption Bug
Written by Michael Larabel in Linux Kernel on 4 March 2021 at 01:50 PM EST. 5 Comments
LINUX KERNEL --
Linus Torvalds has now warned developers over using Linux 5.12-rc1 as a basis for their future branches and is looking to release 5.12-rc2 ahead of schedule as a result of that problematic file-system corruption bug stemming from a swap file bug.

Linus issued a warning over using 5.12-rc1 and renamed the Git tag to "v5.12-rc1-dontuse".
The reason is fairly straightforward: this merge window, we had a very innocuous code cleanup and simplification that raised no red flags at all, but had a subtle and very nasty bug in it: swap files stopped working right. And they stopped working in a particularly bad way: the offset of the start of the swap file was lost.

Swapping still happened, but it happened to the wrong part of the filesystem, with the obvious catastrophic end results.
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Yes, this is very unfortunate, but it really wasn't a very obvious bug, and it didn't even show up in normal testing, exactly because swapfiles just aren't normal. So I'm not blaming the developers in question, and it also wasn't due to the odd timing of the merge window, it was just simply an unusually nasty bug that did get caught and is fixed in the current tree.

But I want everybody to be aware of because _if_ it bites you, it bites you hard, and you can end up with a filesystem that is essentially overwritten by random swap data. This is what we in the industry call "double ungood".

Linus went on to add in a message today that he is looking at carrying out an accelerated Linux 5.12-rc2 release, likely happening tomorrow (Friday) rather than on his usual Sunday cadence.


Linux 5.12-rc1 - or Git prior to yesterday - can easily wreck your file-system if using a swap file... It had been wreaking havoc on test systems here for more than one week.


Of course, if you are a devoted Phoronix reader this shouldn't be surprising: last week I was already warning of data loss issues on Linux 5.12 Git with several of my test systems seeing this nasty file-system corruption on Ubuntu where swapfiles are used several days before 5.12-rc1 was even issued.

The bisecting in such case was slow and then wasn't until Intel's CI systems began seeing corruption and being voiced along with their engineering resources to further investigate was a fix published and merged that landed into Linux 5.12 Git yesterday.

For those enjoying my kernel benchmarking and other Linux performance testing, you can show your support by joining Phoronix Premium or a PayPal tip. Or at the very least, just turn off any ad-blocker. Now that this corruption issue is resolved, I've already been working on some interesting Linux 5.12 performance tests that will begin rolling out shortly.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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