linux-kernel - Re: [REGRESSION] 4.11-rc: systemd doesn't see most devices

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Date:   Tue, 11 Apr 2017 16:31:48 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: [REGRESSION] 4.11-rc: systemd doesn't see most devices

On Tue, Apr 11, 2017 at 05:38:35PM +0200, Greg KH wrote:
> I haven't seen this at all, nor heard of it.  As systemctl only gets
> what udev reports to it, have you tried using 'udevadm' to monitor your
> devices when you plug them in, to ensure it is really seeing them?

The problem is that the problem happens at boot, so I can't really use
"udevadm monitor" --- so I'm not sure whats the best way to debug
this.  I can seen some journalctl logs which do show that it's not
detecting the dm-crypt volume --- but that's insane, because my root
partition is also on the dm-crypt, and it was unlocked in the initrd.
So systemd and udev might not think it exists, but it most definitely
does --- or the boot wouldn't have been able to proceed at all.  

In any case, here is the "udevadm info -e" output from a good and bad
boot, as well as a dmesg from a good and a bad boot.  I'm not seeing
anything obvious, but it does seem interesting that "udevadm info -e"
shows a lot of devices which "systemctl | grep device" doesn't.  Is
there any recent change in the kernel's interfaces that udev depends
on that might make a difference?  For that matter, what does udev
depend on?  Should I be looking at differences in sysfs?  Or does udev
use something else?

I'd do more debugging, but there's a lot of magic these days in the
kernel to udev/systemd communications that I'm quite ignorant about.
Is this a good place I can learn more about how this all works, other
than diving into the udev and systemd sources?  :-(

						- Ted

Download attachment "udevadm.good.gz" of type "application/gzip" (21596 bytes)

Download attachment "udevadm.bad.gz" of type "application/gzip" (15617 bytes)

Download attachment "dmesg.good.gz" of type "application/gzip" (19888 bytes)

Download attachment "dmesg.bad.gz" of type "application/gzip" (16012 bytes)