Anyone facing this..
Could you please make sure to propagate I/O errors properly to
filesystem in order for it to call its automatically shutdown procedure.
After that, the mount won't reference the super block in kernel and that
will allow the device mapper to be destroyed (this can be seen by
checking existence of device-mapper node in
/sys/fs/{xfs,ext3,ext4}/node, saying that the super block is still being
referenced).
I had a recent case where not propagating the error would cause the
filesystem to hang forever, causing lockups and not allowing the device-
mapper tables to be flushed by multipath (or even the OS to be
operational). In this case, if the network is turned off (or
interrupted) before the ISCSI is logged out, then the multipath (dm) and
iscsi (transport) layers HAVE TO propagate the I/O error to the
filesystem for it to shutdown BEFORE the device mapper flush logic is
attempted (by issuing ioctls to /dev/dm-X by multipath or lvm, example).
This is can be done by:
node.session.timeo.replacement_timeout = 0 (iscsid.conf)
(This parameter might be persistent on already discovered LUNs)
USAGE:
iscsiadm -m node -T $target_name -p $target_ip:$port -o update -n \
node.session.timeo.replacement_timeout -v $timeout_value
on already logged/discovered LUNs.
---- AND ----
dev_loss_tmo 10 (multipath.conf)
The fact that the network was removed BEFORE the ISCSI logout happened
is NOT an issue if ROOT device is NOT on ISCSI: You just have to allow
the block device <-> device mapper <-> transport layer SHUTDOWN logic to
WORK before flushing the device-mapper. (Hopefully the umount on _netdev
devices is done, causes an I/O error, filesystem shuts down, multipath
service closes multipath device-mapper devices).
Pay attention because if filesystem is umounted and ISCSI is gone, the
timeout will have to be waited before the error is PROPAGATED to other
layer. So if filesystem is umounted, ONE last superblock inode UPDATE
will be attempted (if no cache in pagecache). This update is to sync
superblock state and update metadata for the filesystem itself. This
update attempt will create an I/O error for the superblock inode (after
time timeout you configured). This will make the filesystem to be
shutdown (a half unmounted state). After shutdown, the logic trying to
umount (synchronously) the filesystem will continue (possibly in
systemd).
If the problem is because of you tried to flush the device mapper and
the filesystem was still referencing the device mapper super block, this
will fade away if the error is propagated and the filesystem is
shutdown, you can attempt doing the flush of device-mapper right after
filesystem shutdown happened.
Could you please try setting the timeouts properly for lower timings and
let me know if that mitigated the issue ?
Thank you
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https://bugs.launchpad.net/bugs/1569925
Title:
Shutdown hang on 16.04 with iscsi targets
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