FBSD 10.0-S (r261289M) under XenServer 6.2 - Stuck sshd in urdlck?

[Roger Pau Monné]

On 17/03/14 17:59, Karl Pielorz wrote:
> 
> Hi,
> 
> I setup a VM a while ago under XenServer 6.2 - it's an amd64 FBSD 10.0-S
> box (based on r261289) - it's running under Xen PVHVM.
> 
> I set it up - and left it for a while (46 days). I went to ssh to it
> today, and got:
> 
> "
> ssh_exchange_identification: Connection closed by remote host
> "
> 
> Getting on to the boxes console there's lots of what look to be 'stuck'
> sshd processes?
> 
> 0  3933  895 0  20  0 84868 6944 urdlck Is -  0:00.01 sshd: unknown
> [priv] (sshd)
> 22  3934 3933 0  20  0     0    0 -      Z  -  0:00.00 <defunct>
> 0  3935 3933 0  20  0 84868 6952 sbwait I  -  0:00.00 sshd: unknown
> [pam] (sshd)
> 0  4338  895 0  20  0 84868 6944 urdlck Is -  0:00.01 sshd: unknown
> [priv] (sshd)
> 22  4339 4338 0  20  0     0    0 -      Z  -  0:00.00 <defunct>
> 
> 
> Anyone know what 'urdlck' is?

It seems like the process is stuck while trying to acquire a rw mutex in
read mode. Could you obtain a backtrace of the process with gdb? Also a
kernel-space dump might be useful, could you also run procstat -k <pid>?

> 
> There's 126 of these processes, e.g.
> 
> 5446  -  I         0:00.00 sshd: unknown [pam] (sshd)
> 5450  -  Is        0:00.01 sshd: unknown [priv] (sshd)
> 5452  -  I         0:00.00 sshd: unknown [pam] (sshd)
> 5453  -  Is        0:00.01 sshd: unknown [priv] (sshd)
> 
> 
> Bearing in mind the box is firewalled from ssh access, and no one (apart
> from me today) has attempted to get onto the box with ssh - this is a
> little concerning. Every about 5-10 connects will actually 'connect' -
> the rest just result in the 'key exchange' error.
> 
> Kernel is GENERIC with:
> 
>   options NO_ADAPTIVE_MUTEXES
>   options NO_ADAPTIVE_RWLOCKS
>   options NO_ADAPTIVE_SX
> 
> There's nothing logged in dmesg, or syslog.
> 
> Is there anything worth doing to this VM before I restart it - i.e. to
> try and figure out what's happened? / troubleshoot?
> 
> -Karl
> 
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