Note: This bug is displayed in read-only format because
the product is no longer active in Red Hat Bugzilla.
RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.
device-mapper is unable to load tables that include offlined devices. So far, I can only see this when I manually offline the device with:
# echo offline > /sys/block/<devname>/device/state
Unfortunately, when multipathd tries to add a path to a multipath device with an offlined path device, it needs to reload the device. This will fail. Worse, multipathd will retry the reload, and will livelock.
If you run multipath, it will segfault. When multipath examines the existing multipath devices, it will see the offlined path. However, since the path is offline, multipath will not have gotten any of the path info, and it will crash trying to select a checker without already having the sysfs info.
I have a fix for this. The ideal fix would be for the device-mapper kernel code to allow new tables with offlined devices, if the old table already included the devices. Instead, I fixed the resulting problems in the multipath code.
multipathd will still not be able to reload the table, but it will add the new path device to the pathlist, where it can be adopted from later, and multipathd won't livelock.
Also multipath will now grab the sysfs pathinfo if necessary before trying to select a checker.
To reproduce this bug
1. Setup a multipath device with multiple paths
2. run
# echo offline > /sys/block/<path1>/device/state
3. run
# echo 1 > /sys/block/<path2>/device/delete
This should fail to remove the path, because you can't reload the table with path1 offlined. Then
4. run
# scsi-rescan
This will make multipathd go into a livelock trying to readd the new path2 device. To see the multipath error
5. kill multipathd
6. run
# multipath
This will segfault, since multipath doesn't get the sysfs info from path1 before it tries to select a checker for it.
If this can actually be hit in without manually offlining the device, this fix will still have the problem that multipathd won't be able to reload the table to add the path back to the multipath device, when it adds the path to its list of available paths. This was true in RHEL5 as well. However it never really bothered people since path devices didn't get removed when they failed. To work around this issue in RHEL6, users can set
dev_loss_tmo and fast_io_fail_tmo to high enough values that their devices never get removed when the fail. This will make RHEL6 work like RHEL 5.
However, I have not been able to recreate this without manually offlining the device, and no testers have reported this problem, so I'm not sure that it will ever come up in normal operations.
Comment 4RHEL Program Management
2010-06-25 04:42:54 UTC
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release. Product Management has requested further
review of this request by Red Hat Engineering, for potential inclusion in a Red
Hat Enterprise Linux Major release. This request is not yet committed for
inclusion.
multipathd now only tries to reload 3 times in ev_add_path if the load fails. Also, multipath will now pull in the sysfs information for devices that lack it. This allows multipath and multipathd to cope with this without segfaulting or getting stuck in inifinte loops.
Comment 12releng-rhel@redhat.com
2010-11-10 20:11:31 UTC
Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.