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To: "freebsd-mips@freebsd.org" <freebsd-mips@freebsd.org>
From: Eugene Grosbein <eugen@grosbein.net>
Subject: LOR on umount
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Date: Sun, 8 Nov 2015 23:51:23 +0700
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Hi!

While trying to reproduce kernel panic using debugging kernel I've got lock order reversal
trying to umount UFS1 /dev/ufs/extflash (/dev/da0s1d) mounted using USB pen
as "async,noatime" (no soft-updates):

# lock order reversal:
 1st 0x81a6ab74 ufs (ufs) @ /home/src/sys/kern/vfs_mount.c:1224
 2nd 0x8276a4b4 devfs (devfs) @ /home/src/sys/ufs/ffs/ffs_vfsops.c:1375
KDB: stack backtrace:
db_trace_thread+30 (?,?,?,?) ra c3b4789000000018 sp 0 sz 0
db_trace_self+1c (?,?,?,?) ra c3b478a800000018 sp 0 sz 0
8008e500+34 (?,?,?,?) ra c3b478c0000001a0 sp 0 sz 0
kdb_backtrace+44 (?,?,?,?) ra c3b47a6000000018 sp 0 sz 0
801ccfd8+34 (?,?,?,?) ra c3b47a7800000020 sp 0 sz 0
witness_checkorder+b24 (?,?,?,55f) ra c3b47a9800000058 sp 0 sz 0
__lockmgr_args+9a8 (?,?,8276a4d4,?) ra c3b47af000000080 sp 0 sz 1
vop_stdlock+4c (?,?,?,?) ra c3b47b7000000028 sp 0 sz 0
VOP_LOCK1_APV+f4 (?,?,?,?) ra c3b47b9800000020 sp 0 sz 0
_vn_lock+8c (?,?,?,?) ra c3b47bb800000050 sp 0 sz 0
ffs_flushfiles+98 (?,?,?,?) ra c3b47c0800000038 sp 0 sz 0
802b4ea8+bc (?,?,?,?) ra c3b47c4000000040 sp 0 sz 0
dounmount+9f0 (80e74560,?,?,?) ra c3b47c8000000060 sp 100000000 sz 0
sys_unmount+2f8 (?,?,?,?) ra c3b47ce0000000e0 sp 0 sz 0
trap+7f0 (?,?,?,?) ra c3b47dc0000000c0 sp 0 sz 0
MipsUserGenException+e8 (?,?,?,4046f520) ra c3b47e8000000000 sp 0 sz 0
pid 694

That's head at r290541.

It was unmounted, though. Seems to be harmless, but who knows...