FreeBSD-HEAD gets stuck on vnode operations

[Konstantin Belousov]

On Mon, May 13, 2013 at 04:33:04PM +0200, Roger Pau Monn? wrote:
> On 13/05/13 13:18, Roger Pau Monn? wrote:
> > The VM can be stuck in this state for quite some time, it generally
> 
> I would like to explain this a little bit more, the syncer process
> doesn't get blocked on the _mtx_trylock_flags_ call, it just continues
> looping forever in what seems to be an endless loop around
> mnt_vnode_next_active/ffs_sync. Also while in this state there is no
> noticeable disk activity, so I'm unsure of what is happening.
How many CPUs does your VM have ?

The loop you describing means that other thread owns the vnode
interlock. Can you track what this thread does ? E.g. look at the
vp->v_interlock.mtx_lock, which is basically a pointer to the struct
thread owning the mutex, clear low bits as needed. Then you can
inspect the thread and get a backtrace.

Does the loop you described stuck on the same vnode during the whole
lock-step time, or is the progress made, possibly slowly ?

I suppose that your HEAD is recent.

> 
> > varies between a couple of minutes (5-10min) to an hour or two, after
> > this the VM recovers itself and resumes normal operation. I still have
> > to test this on a bare metal FreeBSD install, but I would like to ask
> > if someone has seen a similar behaviour, or if someone is suspicious of
> > a change that could cause this.
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