sshfs/nfs cause server lockup

[Kris Kennaway]

On Thu, Nov 23, 2006 at 05:25:21AM +0000, Chris wrote:
> On 22/11/06, Kris Kennaway <kris at obsecurity.org> wrote:
> >On Wed, Nov 22, 2006 at 05:49:12AM +0000, Chris wrote:
> >> On a few occasions all different remote servers I have had nfs cause
> >> servers to stop responding so I stopped  using it all the servers were
> >> either 6.0 release 6.1 release or 6-stable.
> >>
> >> We recently discovered sshfs which supports cross platform mounting
> >> server is linux and I mounted on a freebsd 6.1 release using security
> >> branch up to date.
> >>
> >> it was working fine for around 5 to 6 days with some problems with
> >> sshfs not updating files that are updated but wasnt compromising the
> >> stability of the freebsd server I just remounted to keep up to date.
> >> Then today the linux server had network problems so the sshfs timed
> >> out and there is 2 dirs I mount, the first mounted fine a bit slow but
> >> connected but when I ran the command to mount the 2nd dir the server
> >> stopped responding.
> >>
> >> My 2nd ssh terminal was alive I tried to run top to see if sshfs was
> >> hanging or something but when I hit enter top didnt run and the 2nd
> >> terminal was froze, note both terminals didnt timeout and a ircd
> >> running on the server also did not timeout but the box wasnt listening
> >> to any new requests, it was responding to pings fine.
> >>
> >> I have a remote reboot facility on the box but no local access and no
> >> kvm/serial console facility available this is the case for all of my
> >> servers.  I initially tried a soft reboot which uses ctrl-alt-delete
> >> but the pings kept replying so I could see the reboot wasn initiated
> >> indicating some kind of console lockup as well, I then did a hard
> >> reboot which brought the server back.
> >>
> >> All logs stopped when the first lockup occured so no errors etc.
> >> recorded bear in mind I have no local access to this machine.  It does
> >> appear that 6.x has some kind of serious remote mounting bug because I
> >> never had these nfs problems in freebsd 5.x.
> >>
> >> I would be interested in any thoughts as to what could help me I have
> >> rebooted the server now with network mpsafe disabled to see if this
> >> will help it is using a generic kernel with the following changes.
> >
> >Sounds like your "sshfs" is causing the kernel to deadlock in that
> >error situation.  You can confirm by enabling DEBUG_LOCKS and
> >DEBUG_VFS_LOCKS, then breaking to DDB and running 'show lockedvnods'
> >when the deadlock occurs.
> >
> >If you're still having problems with NFS on 6.2, we'd much rather you
> >reported those so that we can investigate and try to fix them.
> >
> >Kris
> >
> >
> >
> 
> Ok thanks, I will make sure this box is updated to 6.2 when it hits
> release, if I enable the options in the kernel I will need local
> access to use ddb?

Yeah, you'll need a form of console access (local or serial).

In principle you could extract the information from a coredump
(i.e. trigger a coredump when the system deadlocks), but I don't think
there's a kgdb macro equivalent of 'show lockedvnods'.

Kris

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