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Re: [Xen-devel] xenolinux /dev/random

Are you also using Linux as an NFS server? We use Linux extensively
in-house for client machines and have not seen this. Although I'm sure
we don't use the default Linux settings.


On Thu, 13 May 2004, Steven Hand wrote:

> >My goodness!  See the message I just now posted to xen-devel about NFS
> >root hangs; could this be what we're hitting?  The most recent hang we
> >saw happened while an rsync was running over ssh *and* someone restarted
> >apache...
> >
> >This wouldn't cause the "NFS server not responding/NFS server OK"
> >messages on the domain's console, though (or does that show up as a
> >symptom of this too?)
> I don't think this is the cause of the NFS hangs you've been seeing; that
> appears to be a generic linux thing (at least we see it with our regular
> linux boxes as well as with xen boxes); however if you want to test the
> theory the easiest thing to do is to change the /dev/random device node
> to be an alias for /dev/urandom (a non-blocking but potentiallyweaker
> source of randomness).
> The /dev/random bug only really manifested for us during boot, only on
> Xen, and resulted in a permanenent hang.
> The "NFS server foo not responding" followed by later "NFS server foo OK"
> messages from linux appear to be due to a combination of stupid timeouts
> in the linux sunrpc code and another bug which can cause automounters
> to fall into an uninterruptible sleep. If you check "ps auwwx" on a
> machine which is having problems and notice proceesses in state 'D'
> then this is biting you. Even if this doesn't occur, the crappy timeouts
> in the regular linux code mean that linux perfroms very badly if it gets
> any errors/loss/congestion during nfs operations.
> cheers,
> S.
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