[systemd-devel] BTRFS bug with parallel mounts?

[Mike Kazantsev]

On Wed, 10 Nov 2010 15:52:51 -0200
Gustavo Sverzut Barbieri <barbieri at profusion.mobi> wrote:

> On Wed, Nov 10, 2010 at 2:11 PM, Greg KH <greg at kroah.com> wrote:
> > On Wed, Nov 10, 2010 at 01:02:51PM -0200, Gustavo Sverzut Barbieri wrote:
> >> On Wed, Nov 10, 2010 at 9:33 AM, Gustavo Sverzut Barbieri
> >>
> >> Part of the log (sorry, I had no way but to type it all):
> >>
> >> BUG: unable to handle kernel NULL pointer dereference at 0000000000000128
> >> IP: [<ffffffff811329fb>] btrfs_test_super+0xb/0x30
> >> PGD: 26b5b1067 PUD 26a465067 PMD 0
> >> last sysfs file: /sys/devices/virtual/bdi/btrfs-2/uevent
> >> CPU 0
> >> Modules linked in: nvidia(P) lib80211_crypt_tkip wl(P)
> >> Pid: 434, comm: mount Tainted: P     2.6.36 #3 Mac-F22586C8/MacBookPro6,2
> >> RIP: ... btrfs_test_super+0xb/0x30
> >
> > Sounds like a btrfs issue, have you contacted those developers?
> 
> No, I just mailed systemd as people (kay?) seems to be using it, at
> least I saw people here advertising its usage, even the readahead have
> specific code, so maybe people had (or not) issues with it.
> 
> Let's face that mounting multiple points simultaneously is not what
> one would expect.
> 
> 
> > Also, you really are going to have to be able to reproduce this without
> > the closed source kernel modules linked in (broadcom and nvidia) for
> > anyone to even be able to help you out.
> 
> yeah, I'm pretty sure about that ;-)
> 

I can reliably reproduce the issue on my hardware and similar vm setup
with several btrfs mounts, activated during boot.
Kernel spits some backtrace into terminal, then, after a few seconds it
enters some kind of crazy endless error-loop, flooding terminal with
more backtraces.
Vanilla 2.6.36 kernel, no proprietary code.

Since none of these mounts are critical to boot (I didn't trust btrfs
much at the time), I've worked around the issue by
comment=systemd.automount, so they got mounted after boot with systemd.

I thought about reporting the issue when I've encountered it, but been
a bit busy adapting the system for systemd, so it kina slipped off my
mind.
Guess I'll get all these traces, clean my vm from possible private
stuff (I rsync it from a real machine) and report the setup to btrfs
maintainers in a few days.
Thanks for reminder! ;)


-- 
Mike Kazantsev // fraggod.net
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