dm-multipath + scsi_transport_fc interop problems

Bug #163075 reported by Tore Anderson
4
Affects Status Importance Assigned to Milestone
linux (Ubuntu)
Wishlist
Unassigned
linux-source-2.6.22 (Ubuntu)
Undecided
Unassigned

Bug Description

Hi guys. Just want to notify about troubles with using dm-multipath with scsi_transport_fc (a very common combination).

The SCSI transport copes with loss of remote rports by removing the device node. However dm-multipath isn't designed to cope with this, and keeps the internal kernel structures open, preventing them from being removed completely. When the lost rport is revived, the re-addition of the device-node fails with an -EEXIST error. See http://thread.gmane.org/gmane.linux.scsi/36123 for more information.

In addition the device removal causes multipathd to remove paths from the dm map, causing the map to be suspended (also discussed in the post above). This breaks queue_if_no path due to lacking use of no_flush (as I understand it). This is supposedly fixed by multipath-tools 0.4.8, but Ubuntu has yet to upgrade to this version unfortunately.

The other enterprise distros has worked around these problems by adding a patch that allows the user to disable the devnode removal on rport loss. This patch was submitted upstream here http://thread.gmane.org/gmane.linux.scsi/25318 but never made it into the upstream kernels. I get the impression the SCSI people believes they're doing the Right Thing (probably true) and take the hard stance that the dm team is the ones that should fix their end instead, and forcing this by not providing a workaround in the SCSI layer. This of course hurts users, which is probably why SuSE and Red Hat have added the workaround anyway.

I ask you to at least consider following RH and SuSE on this one for the next LTS release (unless dm-multipath is fixed of course).

Regards
Tore Anderson

Revision history for this message
Leann Ogasawara (leannogasawara) wrote :

Hi Tore,

Thank you for your report and helping to make Ubuntu better. Beginning with the Hardy release, the kernel source package naming convention has changed from linux-source-2.6.24 to just linux. Therefore, I'm reassigning to the 'linux' package.

I'll also assign this request to the kernel team. However, note that It is a lot of extra work for the Ubuntu kernel team to maintain out of tree patches. As you probably already know, they typically prefer upstream acceptance before considering to maintain community patches locally. I'll leave it to their discretion regarding the maintenance of this patch in Ubuntu. Thanks!

Changed in linux-source-2.6.24:
assignee: nobody → ubuntu-kernel-team
importance: Undecided → Wishlist
status: New → Triaged
Revision history for this message
Leann Ogasawara (leannogasawara) wrote :

Also just a note, a new task against the actively developed kernel has been opened. However, against linux-source-2.6.22 this does not meet the criteria for a stable release update and will be closed. You can learn more about the stable release update process at https://wiki.ubuntu.com/StableReleaseUpdates . Thanks!

Changed in linux-source-2.6.22:
status: New → Won't Fix
Changed in linux:
assignee: ubuntu-kernel-team → amitk
status: Triaged → In Progress
Revision history for this message
Amit Kucheria (amitk) wrote :

commit d2db70a501ee23037850427e74fc4f2524fa16e4 in the hardy tree

Changed in linux:
status: In Progress → Fix Committed
Revision history for this message
Tim Gardner (timg-tpi) wrote :

Ubuntu-2.6.24-4.7

Changed in linux:
assignee: amitk → nobody
status: Fix Committed → Fix Released
Revision history for this message
Amit Kucheria (amitk) wrote :

It is actually 425c672b07ee537ffe355abae7543eb6da82d295, titled "UBUNTU: SAUCE: make fc transport removal of target configurable"

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