reboot after panic: vm_page_unwire: invalid wire count: 0

Kris Kennaway kris at
Tue Nov 13 16:49:36 PST 2007

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.


>  -Kip
> On Nov 13, 2007 1:59 PM, Vivek Khera <vivek at> 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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