It then might be a problem with "/dev/loop-control" device node. Which
dynamically find or allocate a free device, but also add and remove loop
devices from the running system.
# drivers/block/loop.c
2090 static void loop_remove(struct loop_device *lo)
2091 {
2092 del_gendisk(lo->lo_disk);
2093 blk_cleanup_queue(lo->lo_queue);
2094 blk_mq_free_tag_set(&lo->tag_set);
2095 put_disk(lo->lo_disk);
2096 kfree(lo);
2097 }
2177 case LOOP_CTL_REMOVE:
2178 ret = loop_lookup(&lo, parm);
2179 if (ret < 0)
2180 break;
2181 if (lo->lo_state != Lo_unbound) {
2182 ret = -EBUSY;
2183 break;
2184 }
2185 if (atomic_read(&lo->lo_refcnt) > 0) {
2186 ret = -EBUSY;
2187 break;
2188 }
2189 lo->lo_disk->private_data = NULL;
2190 idr_remove(&loop_index_idr, lo->lo_number);
2191 loop_remove(lo);
2192 break;
--
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1856871
Title:
i/o error if next unused loop device is queried
Status in linux package in Ubuntu:
Incomplete
Status in snapd package in Ubuntu:
Invalid
Status in systemd package in Ubuntu:
New
Status in udev package in Ubuntu:
New
Bug description:
This is reproducible in Bionic and late.
Here's an example running 'focal':
$ lsb_release -cs
focal
$ uname -r
5.3.0-24-generic
The error is:
blk_update_request: I/O error, dev loop2, sector 0
and on more recent kernel:
kernel: [18135.185709] blk_update_request: I/O error, dev loop18,
sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 0 prio class 0
How to trigger it:
$ sosreport -o block
or more precisely the cmd causing the situation inside the block plugin:
$ parted -s $(losetup -f) unit s print
https://github.com/sosreport/sos/blob/master/sos/plugins/block.py#L52
but if I run it on the next next unused loop device, in this case
/dev/loop3 (which is also unused), no errors.
While I agree that sosreport shouldn't query unused loop devices,
there is definitely something going on with the next unused loop
device.
What is differentiate loop2 and loop3 and any other unused ones ?
3 things so far I have noticed:
* loop2 is the next unused loop device (losetup -f)
* A reboot is needed (if some loop modification (snap install, mount loop,
...) has been made at runtime
* I have also noticed that loop2 (or whatever the next unused one is) have
some stat as oppose to other unused loop devices. The stat exist already right
after the system boot for the next unused loop device.
/sys/block/loop2/stat
::::::::::::::
2 0 10 0 1 0 0 0 0 0 0
2 = number of read I/Os processed
10 = number of sectors read
1 = number of write I/Os processed
Explanation of each column:
https://www.kernel.org/doc/html/latest/block/stat.html
while /dev/loop3 doesn't
/sys/block/loop3/stat
::::::::::::::
0 0 0 0 0 0 0 0 0 0 0
Which tells me that something during the boot process most likely
acquired (on purpose or not) the next unused loop and possibly didn't
released it well enough.
If loop2 is generating errors, and I install a snap, the snap squashfs
will take loop2, making loop3 the next unused loop device.
If I query loop3 with 'parted' right after, no errors.
If I reboot, and query loop3 again, then no I'll have an error.
To triggers the errors it need to be after a reboot and it only impact
the first unused loop device available (losetup -f).
This was tested with focal/systemd whic his very close to latest
upstream code.
This has been test with latest v5.5 mainline kernel as well.
For now, I don't think it's a kernel problem, I'm more thinking of a
userspace misbehaviour dealing with loop device (or block device) at
boot.
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