kern/182842: lock order reversal

[Berend de Boer]

>Number:         182842
>Category:       kern
>Synopsis:       lock order reversal
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Oct 08 22:50:01 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Berend de Boer
>Release:        FreeBSD 10.0-ALPHA5 (latest svn)
>Organization:
Xplain Hosting
>Environment:
FreeBSD bmach.nederware.nl 10.0-ALPHA5 FreeBSD 10.0-ALPHA5 #0 r256132: Wed Oct  9 07:55:11 NZDT 2013     root at bmach.nederware.nl:/usr/obj/usr/src/head/sys/BMACH  amd64

>Description:
Oct  9 11:35:00 bmach kernel: lock order reversal:
Oct  9 11:35:00 bmach kernel: 1st 0xfffffe00f2c25f90 bufwait (bufwait) @ /usr/src/head/sys/kern/vfs_bio.c:3049
Oct  9 11:35:00 bmach kernel: 2nd 0xfffff80120adb530 snaplk (snaplk) @ /usr/src/head/sys/ufs/ffs/ffs_snapshot.c:2297
Oct  9 11:35:00 bmach kernel: KDB: stack backtrace:
Oct  9 11:35:00 bmach kernel: db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe011e5e85d0
Oct  9 11:35:00 bmach kernel: kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe011e5e8680
Oct  9 11:35:00 bmach kernel: witness_checkorder() at witness_checkorder+0xd23/frame 0xfffffe011e5e8710
Oct  9 11:35:00 bmach kernel: __lockmgr_args() at __lockmgr_args+0x86c/frame 0xfffffe011e5e8840
Oct  9 11:35:00 bmach kernel: ffs_copyonwrite() at ffs_copyonwrite+0x17a/frame 0xfffffe011e5e88f0
Oct  9 11:35:00 bmach kernel: ffs_geom_strategy() at ffs_geom_strategy+0xdd/frame 0xfffffe011e5e8920
Oct  9 11:35:00 bmach kernel: bufwrite() at bufwrite+0x170/frame 0xfffffe011e5e8970
Oct  9 11:35:00 bmach kernel: ffs_sbupdate() at ffs_sbupdate+0x1c8/frame 0xfffffe011e5e89e0
Oct  9 11:35:00 bmach kernel: ffs_sync() at ffs_sync+0x526/frame 0xfffffe011e5e8ab0
Oct  9 11:35:00 bmach kernel: sync_fsync() at sync_fsync+0x129/frame 0xfffffe011e5e8ae0
Oct  9 11:35:00 bmach kernel: VOP_FSYNC_APV() at VOP_FSYNC_APV+0xf0/frame 0xfffffe011e5e8b10
Oct  9 11:35:00 bmach kernel: sched_sync() at sched_sync+0x34c/frame 0xfffffe011e5e8bb0
Oct  9 11:35:00 bmach kernel: fork_exit() at fork_exit+0x84/frame 0xfffffe011e5e8bf0
Oct  9 11:35:00 bmach kernel: fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe011e5e8bf0
Oct  9 11:35:00 bmach kernel: --- trap 0, rip = 0, rsp = 0xfffffe011e5e8cb0, rbp = 0 ---

>How-To-Repeat:
Happens after reboot.
>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: