Date:	Thu, 25 Jun 2015 23:49:05 +0200
From:	Christian Hesse <list@...rm.de>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: Linux 4.0.6 breaks my disk/lvm/filesystem setup

David Herrmann <dh.herrmann@...il.com> on Thu, 2015/06/25 14:01:
> Hi
> 
> On Thu, Jun 25, 2015 at 9:05 AM, Christian Hesse <list@...rm.de> wrote:
> > Hello everybody,
> >
> > I kind of nailed the issue. Adding CC to Greg for kdbus and to Herbert for
> > the bad commit. Details are below.
> >
> > Christian Hesse <list@...rm.de> on Tue, 2015/06/23 10:14:
> >> with Linux 4.0.5 everything was perfectly fine, Linux 4.0.6 breaks the
> >> setup on one of my systems: Only three of my logical volumes are
> >> available, systemd reports:
> >>
> >> lvm2-pvscan@254:3.service: State 'stop-sigterm' timed out. Killing.
> >>
> >> Followed by a lot of failed dependencies. The setup looks like this:
> >>
> >> NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
> >> sda                   8:0    0 953,9G  0 disk
> >> |-sda1                8:1    0     1M  0 part
> >> |-sda2                8:2    0   256M  0 part  /boot/efi
> >> |-sda3                8:3    0   7,8G  0 part
> >> | |-vg-iso          254:0    0     4G  0 lvm   /srv/iso
> >> | |-vg-persist      254:1    0     2G  0 lvm   /srv/iso/persist
> >> | `-vg-boot         254:2    0   128M  0 lvm   /boot
> >> |-sda4                8:4    0 913,9G  0 part
> >> | `-cvg             254:3    0 913,9G  0 crypt
> >> |   |-cvg-swap      254:4    0     4G  0 lvm   [SWAP]
> >> |   |-cvg-root      254:5    0    40G  0 lvm   /
> >> |   |-cvg-log       254:6    0     1G  0 lvm   /var/log
> >> |   |-cvg-home      254:7    0   500G  0 lvm   /home
> >> |   |-cvg-vbox_win7 254:8    0    32G  0 lvm
> >> |   |-cvg-vbox_win8 254:9    0    32G  0 lvm
> >> |   |-cvg-git       254:10   0    12G  0 lvm   /srv/git
> >> |   `-cvg-chroots   254:11   0    16G  0 lvm   /var/lib/archbuild
> >> `-sda5                8:5    0    32G  0 part
> >>
> >> Another system is just fine, the only difference is a logical volume with
> >> btrfs (cvg-chroots). Possibly the btrfs fixes are involved?
> >
> > I am running Linux 4.0.x with kdbus from Greg's char-misc tree kdbus
> > branch [0] merged, last commit is b69af624a0 ("kdbus: optimize if
> > statements in kdbus_conn_disconnect()"). Everything works fine with Linux
> > 4.0.5 but breaks with 4.0.6 on one of my systems.
> >
> > I bisected the problem and found this to be the bad commit [1]:
> >
> >   From cf8befcc1a5538b035d478424efcc2d50e66928e Mon Sep 17 00:00:00 2001
> >   From: Herbert Xu <herbert@...dor.apana.org.au>
> >   Date: Sat, 16 May 2015 21:16:28 +0800
> >   Subject: netlink: Disable insertions/removals during rehash
> >
> >   [ Upstream commit: Not applicable ]
> >
> >   The current rhashtable rehash code is buggy and can't deal with
> >   parallel insertions/removals without corrupting the hash table.
> >
> >   This patch disables it by partially reverting
> >   c5adde9468b0714a051eac7f9666f23eb10b61f7 ("netlink: eliminate
> >   nl_sk_hash_lock").
> >
> > I can fix my system by booting with kdbus=0 to disable kdbus or by
> > reverting this single commit. Looks like anything deadlocks... Any idea?
> 
> Greg's kdbus tree does not work on 4.0. How exactly did you do the
> back-merge? You need to revert these patches at least to make it work
> on 4.0 (in this order):
>     kdbus: no need to ref current->mm
>     kdbus: use rcu to access exe file in metadata
>     kdbus: pool: use __vfs_read()
> Furthermore, we don't support kdbus on 4.0. So if this does not happen
> on 4.1, I'd recommend staying with 4.1. It'd still be interesting to
> see whether the netlink-locking back-port is indeed broken.

Probably I borked it with my back-merge then...
Everything else worked perfectly fine, though.

I am on 4.1.0 now, which did not have any issues so far.

> Regardless: It is highly unlikely that the netlink commit and kdbus
> are in any way related. Either kdbus triggers some uncommon user-space
> path, or you have a borked kdbus-merge.

I don't know... Possibly the latter. Let's ignore this as it is
unsupported. ;)

Thanks for your support!
-- 
main(a){char*c=/*    Schoene Gruesse                         */"B?IJj;MEH"
"CX:;",b;for(a/*    Chris           get my mail address:    */=0;b=c[a++];)
putchar(b-1/(/*               gcc -o sig sig.c && ./sig    */b/42*2-3)*42);}

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