mdadm race condition causes drop to busybox prompt

[James E. Blair]

Description: Ubuntu 12.04 LTS
Release: 12.04

There seems to be a race condition with mdadm in initramfs-tools. When my server boots, I get a "Dropping to shell." message and a busybox prompt, but no explanation whatsoever for why that happened.

The local-premount/mdadm script does the following:

  degraded_arrays || exit 0
  mountroot_fail || panic "Dropping to a shell."

degraded_arrays calls mdadm and checks its exit code. mountroot_fails also calls degraded_arrays, which calls mdadm again. By changing the degraded_arrays function to echo the exit code from mdadm, I determined that on my server, the first call to mdadm from degraded_arrays returned 4, but the second call from mountroot_fail returned 0. mountroot_fail uses its call to determine whether to output a message about why the user is being dropped into a shell and whether to try to boot in degraded mode. If it's called, but mdadm returns 0, mountroot_fail always exits with an error but no explanation.

It seems very likely that this is a race condition since the two calls to mdadm, which are _very_ close together return different values, with no intervening work having been done by initramfs-tools.

I have corrected this locally by adding a local-top/ script that invokes "wait_for_udev 10".

It seems like there are two issues that should be corrected:

1) The mdadm/udev race condition -- initramfs-tools should have a more solid method of being sure that all the mdadm work is done before it checks if the array is degraded.

2) The lack of explanation for being dropped at a busybox prompt. The code path that checks for a degraded array, checks again, and drops the user at a prompt with no explanation if the values are _different_ makes little sense.