geom: fix initialization order
There's a race between the initialization of devsoftc.mtx (by devinit)
and the creation of the geom worker thread g_run_events, which calls
devctl_queue_data_f. Both of those are initialized at SI_SUB_DRIVERS
and SI_ORDER_FIRST, which means the geom worked thread can be created
before the mutex has been initialized, leading to the panic below:
wpanic: mtx_lock() of spin mutex (null) @ /usr/home/osstest/build.135317.build-amd64-freebsd/freebsd/sys/kern/subr_bus.c:620
cpuid = 3
time = 1
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe003b968710
vpanic() at vpanic+0x19d/frame 0xfffffe003b968760
panic() at panic+0x43/frame 0xfffffe003b9687c0
mtx_lock_flags() at mtx_lock_flags+0x145/frame 0xfffffe003b968810
devctl_queue_data_f() at devctl_queue_data_f+0x6a/frame 0xfffffe003b968840
g_dev_taste() at g_dev_taste+0x463/frame 0xfffffe003b968a00
g_load_class() at g_load_class+0x1bc/frame 0xfffffe003b968a30
g_run_events() at g_run_events+0x197/frame 0xfffffe003b968a70
fork_exit() at fork_exit+0x84/frame 0xfffffe003b968ab0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe003b968ab0
- trap 0, rip = 0, rsp = 0, rbp = 0 --- KDB: enter: panic [ thread pid 13 tid 100029 ] Stopped at kdb_enter+0x3b: movq $0,kdb_why
Fix this by initializing geom at SI_ORDER_SECOND instead of
SI_ORDER_FIRST.
Sponsored by: Citrix Systems R&D
Reviewed by: kevans, markj
Differential revision: https://reviews.freebsd.org/D20148