Trap 12 in vm_page_alloc_after()

[Garrett Wollman]

<<On Mon, 19 Nov 2018 07:09:44 +0200, Konstantin Belousov <kostikbel at gmail.com> said:

> On Sun, Nov 18, 2018 at 08:24:38PM -0500, Garrett Wollman wrote:
>> Has anyone seen this before?  It's on a busy NFS server, but hasn't
>> been observed on any of our other NFS servers.
>> 
>> ------------------------------------------------------------------------
>> Fatal trap 12: page fault while in kernel mode

>> --- trap 0xc, rip = 0xffffffff809a903d, rsp = 0xfffffe17eb8d0710, rbp = 0xfffffe17eb8d0750 ---
>> vm_page_alloc_after() at vm_page_alloc_after+0x15d/frame 0xfffffe17eb8d0750

> What is the line number for vm_page_alloc_after+0x15d ?
> Do you have NUMA enabled on 11 ?

If gdb is to be believed, the trap is at line 1687:

        /*
         *  At this point we had better have found a good page.
         */
        KASSERT(m != NULL, ("missing page"));
        free_count = vm_phys_freecnt_adj(m, -1);
>>>>>>  if ((m->flags & PG_ZERO) != 0)
                vm_page_zero_count--;
        mtx_unlock(&vm_page_queue_free_mtx);
        vm_page_alloc_check(m);

The faulting instruction is:

0xffffffff809a903d <vm_page_alloc_after+349>:   testb  $0x8,0x5a(%r14)

There are no options matching /numa/i in the configuration.  (This is
a non-debugging configuration so the KASSERT is inoperative, I
assume.)  I have about a dozen other servers with the same kernel and
they're not crashing, but obviously they all have different loads and
sets of active clients.

-GAWollman