Unable to dump to multipath root filesystem on ppc64el

[Dave Chiluk]

Reproducer
1. Deploy trusty on a multipath rooted machine *(tested on ppc64el, may affect x86 as well).
2. Install 3.16 kernel *(has not been verified with other kernels).
3. sudo apt-get install linux-crashdump
4. Set USE_KDUMP=1 in /etc/default/kdump-tools
5. Set crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M@32M
in /etc/default/grub.d/kexec-tools.cfg
6. update-grub
7. reboot
8. echo 1 > /proc/sys/kernel/sysrq
9. echo c > /proc/sysrq-trigger

Full console output attached.
 --------------------------------------Interesting parts of console output --------------------------------------
[ 33.160186] sd 0:2:5:0: alua: port group c289 state A preferred supports TOlUSNA
[ 33.160324] sd 0:2:5:0: alua: Attached
[ 33.160396] alua: device handler registered
done.
Begin: Running /scripts/init-premount ... done.
Begin: Mounting root file system ... Begin: Running /scripts/local-top ... Begin: Loading multipath modules ... Success: loaded module dm-multipath.
Failure: failed to load module dm-emc.
done.
Begin: Starting multipathd ... [ 33.194232] multipathd (253): /proc/253/oom_adj is deprecated, please use /proc/253/oom_score_adj instead.
[ 33.197208] random: nonblocking pool is initialized
done.
Begin: Loading essential drivers ... done.
Begin: Running /scripts/init-premount ... done.
Begin: Mounting root file system ... Begin: Running /scripts/local-top ... Begin: Loading multipath modules ... Success: loaded module dm-multipath.
Failure: failed to load module dm-emc.
done.
Begin: Starting multipathd ... done.
Gave up waiting for root device. Common problems:
 - Boot args (cat /proc/cmdline)
   - Check rootdelay= (did the system wait long enough?)
   - Check root= (did the system wait for the right device?)
 - Missing modules (cat /proc/modules; ls /dev)
ALERT! /dev/mapper/mpath0-part2 does not exist. Dropping to a shell!
[ 213.258259] hidraw: raw HID events driver (C) Jiri Kosina

BusyBox v1.21.1 (Ubuntu 1:1.21.0-1ubuntu1) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) [ 396.459853] ipr 0003:04:00.0: 9076: Configuration error, missing remote IOA
[ 396.459935] ipr 0003:04:00.0: Attached Adapter not discovered within allotted time [PRC: 17101541]
[ 396.460023] ipr 0003:04:00.0: Remote IOA VPID/SN: 00000000
[ 396.460085] ipr 0003:04:00.0: Remote IOA WWN: 0000000000000000
[ 396.460148] ipr: 00000000: 01000000 00000100 F4220000 00000000
[ 396.460210] ipr: 00000010: 4C494344 49424D20 20202020 35374438
[ 396.460271] ipr: 00000020: 30303153 4953494F 41202020 00000000
[ 396.460333] ipr: 00000030: 30303431 4A303337 50050760 5EC28900

[Dave Chiluk (chiluk)]

This may also affect initramfs-tools, as that will likely be the place that any fix needs to be implemented.