10.2-STABLE amd64 panic: page fault while in kernel mode

[Frank Razenberg]

After upgrading from 9.2 to 10.1 I first started noticing panics. They 
occurred roughly weekly and since this storage machine isn't frequently 
used I didn't look into it much further. After updating for 10.2-STABLE 
the panics have gone from weekly to daily.
The machine has 32GB of non-registered ECC DDR3-1066 RAM. There's also a 
10-disk raidz2 pool. I've ran memtest86+ for 72 hours straight with no 
errors.

Crash dumps all feature the following:

Fatal trap 12: page fault while in kernel mode
cpuid = 2; apic id = 12
fault virtual address   = 0x1d1c0bec0
fault code              = supervisor read data, page not present
instruction pointer     = 0x20:0xffffffff804fda65
stack pointer           = 0x28:0xfffffe0698f21870
frame pointer           = 0x28:0xfffffe0698f218d0
code segment            = base 0x0, limit 0xfffff, type 0x1b
                         = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 6106 (pickup)
trap number             = 12
panic: page fault
cpuid = 2


(kgdb) bt
#0  doadump (textdump=<value optimized out>) at pcpu.h:219
#1  0xffffffff8053ce32 in kern_reboot (howto=260) at 
/usr/src/sys/kern/kern_shutdown.c:455
#2  0xffffffff8053d215 in vpanic (fmt=<value optimized out>, ap=<value 
optimized out>) at /usr/src/sys/kern/kern_shutdown.c:762
#3  0xffffffff8053d0a3 in panic (fmt=0x0) at 
/usr/src/sys/kern/kern_shutdown.c:691
#4  0xffffffff807755db in trap_fatal (frame=<value optimized out>, 
eva=<value optimized out>) at /usr/src/sys/amd64/amd64/trap.c:851
#5  0xffffffff807758dd in trap_pfault (frame=0xfffffe0698dbc7c0, 
usermode=<value optimized out>) at /usr/src/sys/amd64/amd64/trap.c:674
#6  0xffffffff80774f7a in trap (frame=0xfffffe0698dbc7c0) at 
/usr/src/sys/amd64/amd64/trap.c:440
#7  0xffffffff8075b0f2 in calltrap () at 
/usr/src/sys/amd64/amd64/exception.S:236
#8  0xffffffff804fda65 in kqueue_close (fp=0xfffff803e4967190, 
td=0xfffff80014b094a0) at /usr/src/sys/kern/kern_event.c:1750
#9  0xffffffff804f25f9 in _fdrop (fp=0xfffff803e4967190, 
td=0xfffff802b5d2a000) at file.h:343
#10 0xffffffff804f4e9e in closef (fp=<value optimized out>, td=<value 
optimized out>) at /usr/src/sys/kern/kern_descrip.c:2338
#11 0xffffffff804f4ab9 in fdescfree (td=0xfffff80014b094a0) at 
/usr/src/sys/kern/kern_descrip.c:2106
#12 0xffffffff805013a9 in exit1 (td=0xfffff80014b094a0, rv=<value 
optimized out>) at /usr/src/sys/kern/kern_exit.c:369
#13 0xffffffff80500e3e in sys_sys_exit (td=0xfffffe000782e060, 
uap=<value optimized out>) at /usr/src/sys/kern/kern_exit.c:179
#14 0xffffffff80775efd in amd64_syscall (td=0xfffff80014b094a0, 
traced=0) at subr_syscall.c:134
#15 0xffffffff8075b3db in Xfast_syscall () at 
/usr/src/sys/amd64/amd64/exception.S:396
#16 0x000000080120335a in ?? ()

Most of the dumps list 'pickup' as current process. All of them have 
'kqueue_close' in the backtrace.
I'm not sure what the next step in diagnosing the issue is. Any pointers 
would be greatly appreciated.

-Frank