Possible workaround w/ losetup.
# uname -rv
5.15.0-69-generic #76-Ubuntu SMP Fri Mar 17 17:19:29 UTC 2023
# cat /sys/module/loop/parameters/max_loop
8
# losetup -nl | sort
/dev/loop0 0 0 1 1 /var/lib/snapd/snaps/lxd_24322.snap
0 512
/dev/loop1 0 0 1 1 /var/lib/snapd/snaps/snapd_18357.snap
0 512
/dev/loop2 0 0 1 1 /var/lib/snapd/snaps/core20_1822.snap
0 512
# ls -1 /dev/loop*
/dev/loop-control
/dev/loop0
/dev/loop1
/dev/loop2
/dev/loop3
/dev/loop4
/dev/loop5
/dev/loop6
/dev/loop7
# truncate -s 1g test1
# truncate -s 1g test2
# ls -lh test1 test2
-rw-r--r-- 1 root root 1.0G Apr 6 17:40 test1
-rw-r--r-- 1 root root 1.0G Apr 6 17:40 test2
# losetup /dev/loop7 test1
# losetup /dev/loop8 test2
losetup: /dev/loop8: failed to set up loop device: No such device or address
...
# losetup --show --find test1
/dev/loop3
# losetup --show --find test1
/dev/loop4
# losetup --show --find test1
/dev/loop5
# losetup --show --find test1
/dev/loop6
# losetup --show --find test1
/dev/loop8
# losetup --show --find test1
/dev/loop9
# losetup --show --find test1
/dev/loop10
# losetup --show --find test1
/dev/loop11
# losetup --show --find test1
/dev/loop12
# losetup --show --find test1
/dev/loop13
# strace -e ioctl losetup --show --find test1
ioctl(3, LOOP_CTL_GET_FREE) = 14
ioctl(4, LOOP_CONFIGURE, {fd=3, block_size=0, info={lo_offset=0, lo_number=0,
lo_flags=0, lo_file_name="/root/test1", ...}}) = 0
/dev/loop14
+++ exited with 0 +++
# losetup -d /dev/loop3
# losetup -d /dev/loop4
# losetup -d /dev/loop5
# losetup -d /dev/loop6
# losetup -d /dev/loop8
# losetup -d /dev/loop9
# losetup -d /dev/loop10
# losetup -d /dev/loop11
# losetup -d /dev/loop12
# losetup -d /dev/loop13
# losetup /dev/loop8 test2
#
works now.
# cat /sys/module/loop/parameters/max_loop
8
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You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux-hwe-5.15 in Ubuntu.
https://bugs.launchpad.net/bugs/2015400
Title:
losetup with mknod fails on jammy with kernel 5.15.0-69-generic
Status in linux package in Ubuntu:
Confirmed
Status in linux-hwe-5.15 package in Ubuntu:
New
Bug description:
losetup fails with devices created manually by mknod on kernel
5.15.0-69-generic
# fallocate -l 1G test
# mknod -m 660 /dev/loop8 b 7 8
# chown root:disk /dev/loop8
# losetup /dev/loop8 ./test
losetup: ./test: failed to set up loop device: Device or resource busy
Possibly as a result of this patch:
https://lore.kernel.org/lkml/20221208200605.756287-1-isaacmanjar...@google.com/T/
which was introduced in 5.15.0-68:
http://launchpadlibrarian.net/653145495/linux_5.15.0-67.74_5.15.0-68.75.diff.gz
On a machine prior to this change (no issue with losetup):
# cat /sys/module/loop/parameters/max_loop
0
# uname -r
5.15.0-58-generic
On a machine after the change (has losetup issue as described above):
# cat /sys/module/loop/parameters/max_loop
8
# uname -r
5.15.0-69-generic
So it looks like the default changed and the max amount of loop
devices that can be created with mknod (not loop-control) is 8. If we
set max_loop=0 on the kernel command line, it works as before. Cannot
unload and reload module on a running system to change the parameter
because it is built into the kernel.
Another workaround is to use `losetup --find` but that means you
cannot create with named devices created with mknod.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2015400/+subscriptions
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