On Wed, Mar 24, 2021 at 12:37:03PM +0000, Gulam Mohamed wrote: > Hi All, > > We are facing a stale link (of the device) issue during the iscsi-logout > process if we use parted command just before the iscsi logout. Here are the > details: > > As part of iscsi logout, the partitions and the disk will be removed. The > parted command, used to list the partitions, will open the disk in RW mode > which results in systemd-udevd re-reading the partitions. This will trigger > the rescan partitions which will also delete and re-add the partitions. So, > both iscsi logout processing and the parted (through systemd-udevd) will be > involved in add/delete of partitions. In our case, the following sequence of > operations happened (the iscsi device is /dev/sdb with partition sdb1): > > 1. sdb1 was removed by PARTED > 2. kworker, as part of iscsi logout, couldn't remove sdb1 as it was > already removed by PARTED > 3. sdb1 was added by parted > 4. sdb was NOW removed as part of iscsi logout (the last part of the > device removal after remoing the partitions) > > Since the symlink /sys/class/block/sdb1 points to > /sys/class/devices/platform/hostx/sessionx/targetx:x:x:x/x:x:x:x/block/sdb/sdb1 > and since sdb is already removed, the symlink /sys/class/block/sdb1 will be > orphan and stale. So, this stale link is a result of the race condition in > kernel between the systemd-udevd and iscsi-logout processing as described > above. We are able to reproduce this even with latest upstream kernel. > > We have come across a patch from Ming Lei which was created for "avoid to > drop & re-add partitions if partitions aren't changed": > https://lore.kernel.org/linux-block/20210216084430.ga23...@lst.de/T/
BTW, there is a newer version of this patchset: https://lore.kernel.org/linux-block/20210224081825.ga1...@lst.de/#r > > This patch could resolve our problem of stale link but it just seems to be a > work-around and not the actual fix for the race. We were looking for help to > fix this race in kernel. Do you have any idea how to fix this race condition? > IMO, that isn't a work-around, kernel shouldn't drop partitions if partition table isn't changed. But Christoph thought the current approach is taken since beginning of kernel, and he suggested to fix systemd-udev. Thanks, Ming
