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Re: Xen hangs (NetBSD 7.0.1, amd64, Xen 4.5.3)

On Wed, Nov 09, 2016 at 09:16:47PM +0000, Alaric Snell-Pym wrote:
> On 17/10/16 18:43, Manuel Bouyer wrote:
> > this means that they're all stuck on a lock.
> > The first thing would be to use ddb (or crash(8), if this works on Xen)
> > to find where in the kernel these processes are stuck.
> > 
> > The next step would be to which which process is actaully holding the lock
> > (this one is probably not in tstile state)
> > 
> Thanks, Manuel... looks like crash(8) works, I'll check that out next
> time it happens! Does the lock show as the "wait channel" as shown by
> ps/w?

yes, but you won't probably find anything interesting this way.
ps/a is more usefull because you can then use tr/a with the lwp address.

> How do I find what process currently holds it? And then I guess I
> do a "trace/t" on the pids involved to see what's what? I'm a little
> green with ddb.

To find the process holding the lock you have to poke around.
Usually it's waiting on something else. You're probably looking for a
Xen-related process.

Also, rebuilding a kernel with options LOCKDEBUG may help.

Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference

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