Memory modified after free, seemingly geli related

[Ed Maste]

I've encountered a few memory modified after free panics recently,
which seem to be from geli. I don't yet have any debugging to
completely confirm it's geli, but it has not happened on my other test
laptop which configured similarly but without geli.

This has a few local patches from my to-commit-to-HEAD queue.
FreeBSD volta 11.0-CURRENT FreeBSD 11.0-CURRENT #10
r284409+6a002d9(staging): Tue Jul  7 17:57:01 EDT 2015

panic: Memory modified after free 0xfffff80009d504d8(248) val=0 @
0xfffff80009d50518

cpuid = 1
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe011414a880
vpanic() at vpanic+0x189/frame 0xfffffe011414a900
panic() at panic+0x43/frame 0xfffffe011414a960
trash_ctor() at trash_ctor+0x48/frame 0xfffffe011414a970
uma_zalloc_arg() at uma_zalloc_arg+0x573/frame 0xfffffe011414a9e0
g_clone_bio() at g_clone_bio+0x1d/frame 0xfffffe011414aa00
g_eli_start() at g_eli_start+0xbd/frame 0xfffffe011414aa30
g_io_schedule_down() at g_io_schedule_down+0xe6/frame 0xfffffe011414aa60
g_down_procbody() at g_down_procbody+0x7d/frame 0xfffffe011414aa70
fork_exit() at fork_exit+0x84/frame 0xfffffe011414aab0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe011414aab0
--- trap 0, rip = 0, rsp = 0xfffffe011414ab70, rbp = 0 ---