6-stable locking problem

[Pavel Merdin]

Hello.

There's  a problem with a very busy server (ad server, CPU is close to
0% idle most of the time).
Configuration: Dual AMD Opteron 252 2.6GHz
Chipset: AMD 8131
Integrated LAN Controller: Broadcom BCM5704 dual-channel GbE Gigabit
Adaptec AIC-7902W Ultra 320 SCSI controller
amr0: <LSILogic MegaRAID 1.53>

We tried both 6.1-RELEASE and 6-STABLE amd64 kernels. (bge driver is
always from recent stable with full Broadcom support).

The  server hangs one or more times a day. It even hangs for some time
right  after  boot  sequence  finishes  (when "login:" prompt occurs).
During  a hang everything stops, even keyboard (interrupts).

We already removed PREEMPTION and linux support.
Sometimes the server can panic with:
  Sleeping thread (tid 100006, pid 4) owns a non-sleepable lock
  panic: sleeping thread
  cpuid=0
  KDB: enter: panic
and hangs there without even starting a debugger.
pid 4 seems to be [g_down]

Today I compiled a kernel with INVARIANTS and WITTNESS.
Right after booting sequence I got the following:

Aug 10 04:37:09 ad1 kernel: lock order reversal: (Giant after non-sleepable)
Aug 10 04:37:09 ad1 kernel: 1st 0xffffff026c4ebe70 AMR List Lock (AMR List Lock) @ dev/amr/amr.c:403
Aug 10 04:37:09 ad1 kernel: 2nd 0xffffffff8073adc0 Giant (Giant) @ vm/vm_contig.c:579
Aug 10 04:37:09 ad1 kernel: KDB: stack backtrace:
Aug 10 04:37:09 ad1 kernel: kdb_backtrace() at kdb_backtrace+0x37
Aug 10 04:37:09 ad1 kernel: witness_checkorder() at witness_checkorder+0x6fb
Aug 10 04:37:09 ad1 kernel: _mtx_lock_flags() at _mtx_lock_flags+0x9a
Aug 10 04:37:09 ad1 kernel: contigmalloc() at contigmalloc+0x57
Aug 10 04:37:09 ad1 kernel: alloc_bounce_pages() at alloc_bounce_pages+0x75
Aug 10 04:37:09 ad1 kernel: bus_dmamap_create() at bus_dmamap_create+0x149
Aug 10 04:37:09 ad1 kernel: amr_alloccmd_cluster() at amr_alloccmd_cluster+0x102
Aug 10 04:37:09 ad1 kernel: amr_alloccmd() at amr_alloccmd+0x55
Aug 10 04:37:09 ad1 kernel: amr_bio_command() at amr_bio_command+0x27
Aug 10 04:37:09 ad1 kernel: amr_startio() at amr_startio+0x6a
Aug 10 04:37:09 ad1 kernel: amr_submit_bio() at amr_submit_bio+0x51
Aug 10 04:37:09 ad1 kernel: amrd_strategy() at amrd_strategy+0x23
Aug 10 04:37:09 ad1 kernel: g_disk_start() at g_disk_start+0x17d
Aug 10 04:37:09 ad1 kernel: g_io_schedule_down() at g_io_schedule_down+0x189
Aug 10 04:37:09 ad1 kernel: g_down_procbody() at g_down_procbody+0x80
Aug 10 04:37:09 ad1 kernel: fork_exit() at fork_exit+0xdf
Aug 10 04:37:09 ad1 kernel: fork_trampoline() at fork_trampoline+0xe
Aug 10 04:37:09 ad1 kernel: --- trap 0, rip = 0, rsp = 0xffffffffb8e8bd00, rbp = 0 ---

Any advice (except suggestion of switching to Linux) ?

-- 
/ Pavel Merdin
Fotki Inc.