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Bug#787561: marked as done (modules virtio_net and virtio_pci are allowed to be removed but they should not be)

Your message dated Sat, 24 Apr 2021 05:13:48 -0700 (PDT)
with message-id <60840b7c.1c69fb81.1fca9.7c15@mx.google.com>
and subject line Closing this bug (BTS maintenance for src:linux bugs)
has caused the Debian Bug report #787561,
regarding modules virtio_net and virtio_pci are allowed to be removed but they should not be
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
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-- 
787561: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787561
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message --- 
Package: linux-image-3.16.0-4-amd64
Version: 3.16.7-ckt9-3~deb8u1
Severity: important

Note: I'm not sure which package to blame here. I chose the kernel
because I believe the kernel knows better than anybody else which
modules are suitable to be unloaded and which modules are not, but
this could also be a bug in qemu or a bug in kmod, so feel free to
reassign.


rmmod(8) says:

  -f, --force
      This option can be extremely dangerous: it has no effect unless CONFIG_MODULE_FORCE_UNLOAD was set when
      the kernel was compiled. With this option, you can remove modules which are being used, or which are not
      designed to be removed, or have been marked as unsafe (see lsmod(8)).

which implicitly means that as long as you don't use --force, rmmod
will refuse to remove a module if it's being used.

Well, I tried this today on a virtual machine running qemu:

lsmod | awk '$3 == 0 { print $1 }' | xargs -r rmmod

and the machine *crashed*, which I think it should count as
"module being used" or "not designed to be removed".


To debug this, I tried to remove modules one by one until problems
started to appear. This is the result:

Attach "lsmod-starting-point.txt" is the output of lsmod before the tests.

Attach "modules-that-may-be-removed.txt" is the list of modules that may
be removed safely, this way:

rmmod `cat modules-that-may-be-removed.txt`

After that, the output of lsmod is like this:

Module                  Size  Used by
evdev                  17445  1
autofs4                35529  2
ext4                  473802  1
crc16                  12343  1 ext4
mbcache                17171  1 ext4
jbd2                   82413  1 ext4
virtio_net             26553  0
virtio_blk             17345  3
virtio_pci             17389  0
virtio_ring            17513  3 virtio_blk,virtio_net,virtio_pci
virtio                 13058  3 virtio_blk,virtio_net,virtio_pci

and now it comes the fun part:

I'm not using the console but ssh. So I'm using the net.
However:

rmmod virtio_net

works and makes the ssh connection to be lost.

I think this should not happen.


Then it comes the really fun part:

rmmod virtio_pci

also works, but the result is I/O error in the root partition,
which becomes read-only and the system needs to be rebooted.
See last attach "screenshot.png".

I think this should not happen either.


Thanks.
Module                  Size  Used by
joydev                 17063  0 
hid_generic            12393  0 
ppdev                  16782  0 
usbhid                 44460  0 
evdev                  17445  2 
hid                   102264  2 hid_generic,usbhid
psmouse                99143  0 
serio_raw              12849  0 
pcspkr                 12595  0 
virtio_console         22655  0 
virtio_balloon         13047  0 
pvpanic                12563  0 
parport_pc             26300  0 
parport                35749  2 ppdev,parport_pc
ttm                    77862  0 
drm_kms_helper         49210  0 
processor              28221  0 
thermal_sys            27642  1 processor
drm                   249955  2 ttm,drm_kms_helper
i2c_piix4              20864  0 
i2c_core               46012  3 drm,i2c_piix4,drm_kms_helper
button                 12944  0 
autofs4                35529  2 
ext4                  473802  1 
crc16                  12343  1 ext4
mbcache                17171  1 ext4
jbd2                   82413  1 ext4
virtio_net             26553  0 
virtio_blk             17345  3 
ata_generic            12490  0 
crc32c_intel           21809  0 
ehci_pci               12512  0 
uhci_hcd               43499  0 
ehci_hcd               69837  1 ehci_pci
usbcore               195340  4 uhci_hcd,ehci_hcd,ehci_pci,usbhid
usb_common             12440  1 usbcore
ata_piix               33592  0 
floppy                 65068  0 
virtio_pci             17389  0 
virtio_ring            17513  5 virtio_blk,virtio_net,virtio_pci,virtio_balloon,virtio_console
virtio                 13058  5 virtio_blk,virtio_net,virtio_pci,virtio_balloon,virtio_console
libata                177457  2 ata_generic,ata_piix
scsi_mod              191405  1 libata

joydev
hid_generic
ppdev
usbhid
hid
psmouse
serio_raw
pcspkr
virtio_console
virtio_balloon
pvpanic
parport_pc
parport
ttm
drm_kms_helper
processor
thermal_sys
drm
i2c_piix4
i2c_core
button
ata_generic
crc32c_intel
ehci_pci
uhci_hcd
ehci_hcd
usbcore
usb_common
ata_piix
floppy
libata
scsi_mod

Attachment: screenshot.png
Description: PNG image


--- End Message ---
--- Begin Message --- 
Hi

This bug was filed for a very old kernel or the bug is old itself
without resolution.

If you can reproduce it with

- the current version in unstable/testing
- the latest kernel from backports

please reopen the bug, see https://www.debian.org/Bugs/server-control
for details.

Regards,
Salvatore

--- End Message ---
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