this post was submitted on 09 Dec 2023
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PSA: Do not upgrade to linux 6.1.64-1 (sopuli.xyz)
submitted 11 months ago by [email protected] to c/[email protected]
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If you are on the stable kernel and use ext4, do not upgrade to linux kernel package 6.1.64-1

It has a bad data corruption bug

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1057843

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[–] [email protected] 5 points 11 months ago

Its in several more kernels than that.

That patch was backported into known (and probably more): v5.10.202, v5.15.140, v6.1.64

ext4 data corruption in 6.1 stable tree (was Re: [PATCH 5.15 000/297] 5.15.140-rc1 review

So I've got back to this and the failure is a subtle interaction between iomap code and ext4 code. In particular that fact that commit 936e114a245b6 ("iomap: update ki_pos a little later in iomap_dio_complete") is not in stable causes that file position is not updated after direct IO write and thus we direct IO writes are ending in wrong locations effectively corrupting data. The subtle detail is that before this commit if ->end_io handler returns non-zero value (which the new ext4 ->end_io handler does), file pos doesn't get updated, after this commit it doesn't get updated only if the return value is < 0.

The commit got merged in 6.5-rc1 so all stable kernels that have 91562895f803 ("ext4: properly sync file size update after O_SYNC direct IO") before 6.5 are corrupting data - I've noticed at least 6.1 is still carrying the problematic commit. Greg, please take out the commit from all stable kernels before 6.5 as soon as possible, we'll figure out proper backport once user data are not being corrupted anymore. Thanks!

https://lore.kernel.org/stable/20231205122122.dfhhoaswsfscuhc3@quack3/