CUREENT issue with ballon.c

[Outback Dingo]

--- trap 0, rip = 0, rsp = 0xfffffe00002c6b70, rbp = 0 ---
uma_zalloc_arg: zone "16" with the following non-sleepable locks held:
exclusive sleep mutex balloon_lock (balloon_lock) r = 0
(0xffffffff816e9c58) locked @ /usr/src/sys/dev/xen/balloon/balloon.c:339
exclusive sleep mutex balloon_mutex (balloon_mutex) r = 0
(0xffffffff816e9c38) locked @ /usr/src/sys/dev/xen/balloon/balloon.c:373
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame
0xfffffe00002c67c0
kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe00002c6870
witness_warn() at witness_warn+0x4a8/frame 0xfffffe00002c6930
uma_zalloc_arg() at uma_zalloc_arg+0x3b/frame 0xfffffe00002c69a0
malloc() at malloc+0x101/frame 0xfffffe00002c69f0
balloon_process() at balloon_process+0x44a/frame 0xfffffe00002c6a70
fork_exit() at fork_exit+0x84/frame 0xfffffe00002c6ab0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe00002c6ab0
--- trap 0, rip = 0, rsp = 0xfffffe00002c6b70, rbp = 0 ---
uma_zalloc_arg: zone "16" with the following non-sleepable locks held:
exclusive sleep mutex balloon_lock (balloon_lock) r = 0
(0xffffffff816e9c58) locked @ /usr/src/sys/dev/xen/balloon/balloon.c:339
exclusive sleep mutex balloon_mutex (balloon_mutex) r = 0
(0xffffffff816e9c38) locked @ /usr/src/sys/dev/xen/balloon/balloon.c:373
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame
0xfffffe00002c67c0
kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe00002c6870
witness_warn() at witness_warn+0x4a8/frame 0xfffffe00002c6930
uma_zalloc_arg() at uma_zalloc_arg+0x3b/frame 0xfffffe00002c69a0
malloc() at malloc+0x101/frame 0xfffffe00002c69f0
balloon_process() at balloon_process+0x44a/frame 0xfffffe00002c6a70
fork_exit() at fork_exit+0x84/frame 0xfffffe00002c6ab0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe00002c6ab0
--- trap 0, rip = 0, rsp = 0xfffffe00002c6b70, rbp = 0 ---
uma_zalloc_arg: zone "16" with the following non-sleepable locks held: