reboot after panic: vm_page_unwire: invalid wire count: 0

[Kip Macy]

Various calls that downgrade permissions or virtually copy a pmap in
pmap.c now remove PG_W (and did not 6 months ago). This may be the
cause of the regression. It would probably be better (and faster) if
the pages were "held" instead of wired.

    -Kip

On Nov 13, 2007 4:49 PM, Kris Kennaway <kris at freebsd.org> wrote:
> Kip Macy wrote:
> > Unfortunately, ZERO_COPY_SOCKETs have long been a known source of
> > problems. I think also, when a page is copied as part of COW the new
> > page is unwired (see pmap_copy et al.), this could lead to
> > socow_iodone unwiring after send a page that was not wired. An added
> > issue is that parts of the VM assume that COW and wired are mutually
> > exclusive which the socow code violates.
> >
> > At some point in the near future I may be adding support for doing
> > zero copy send without COW for blocking sockets. The one down side of
> > this approach is that if you have multiple threads in your process it
> > widens the window during which they can stomp on data that you're
> > sending. Nonetheless, this would be a bug in the application code.
> > More complicated would be zero-copy non-COW send on non-blocking
> > sockets as it would require an extension to kevent for completion
> > notification.
> >
> > In the meantime, your best bet is to disable ZERO_COPY_SOCKETS.
>
> There is a chance this was a recent regression, previously in 7.0 they
> were believed to work.
>
> Kris
>
>
> >
> >
> >  -Kip
> >
> >
> >
> > On Nov 13, 2007 1:59 PM, Vivek Khera <vivek at khera.org> wrote:
> >> On Nov 13, 2007, at 4:50 PM, Vlad GALU wrote:
> >>
> >>>>        vmio = 1
> >>>>        offset = Unhandled dwarf expression opcode 0x93
> >>>> (kgdb)
> >>>>
> >>>    Do you happen to have ZERO_COPY_SOCKETS in your kernel config?
> >>>
> >>>
> >> Yes, I do.  Are they known to be bad under certain loads or just in
> >> general.  I don't have this issue with any other web server running
> >> the same kernel config but those are amd64 boxes mostly.
> >>
> >>
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>
>