[Bug 2083845] Re: Setting I/O scheduler to 'none' causes error in oracular

** Tags removed: verification-needed-oracular-linux
** Tags added: verification-done-oracular-linux

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https://bugs.launchpad.net/bugs/2083845

Title:
Setting I/O scheduler to 'none' causes error in oracular

Status in linux package in Ubuntu:
New
Status in linux-gcp package in Ubuntu:
Fix Released

Bug description:
[Impact]
With Oracular linux-gcp kernel version 6.11.0-1002.2, running the google-guest-agent causes an error. The guest-agent sets the I/O scheduler to 'none', causing errors such as below:

```
2024-10-07T09:24:03.262548+00:00 oracular-old-gga-test google_guest_agent[1125]: panic: invalid return from write: got 256 from a write of 4
```

With strace, we can also see that the return value of write is
unexpected:

[pid 3127] write(7, "none", 4) = 256

This is breaking provision of GCP cloud images, so bump it to
Critical.

[Fix]

Fix commit is e3accac1a976e65491a9b9fba82ce8ddbd3d2389 ("block: Fix
elv_iosched_local_module handling of "none" scheduler").

[How to test]

Apply the fix, rebuild the kernel and try to change scheduler in
sysfs, e.g.:

# echo "none" > /sys/devices/virtual/block/loop1/queue/scheduler
# echo $?
0

[Regression potential]

Upstream clean cherry-pick, already part of v6.11.2.

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