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Date:      Mon, 28 Sep 2009 17:52:23 +0200
From:      Borja Marcos <borjam@sarenet.es>
To:        freebsd-stable@freebsd.org
Subject:   [LOR] unmounting a filesystem
Message-ID:  <800887B3-34CB-49D5-8C0D-F1BB2DC5CA64@sarenet.es>

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Sep 28 19:47:46  kernel: lock order reversal:
Sep 28 19:47:46  kernel: 1st 0xffffff0002a9a308 ufs (ufs) @ /usr/src/ 
sys/kern/vfs_mount.c:1200
Sep 28 19:47:46  kernel: 2nd 0xffffff0002a63a58 devfs (devfs) @ /usr/ 
src/sys/ufs/ffs/ffs_vfsops.c:1194
Sep 28 19:47:46  kernel: KDB: stack backtrace:
Sep 28 19:47:46  kernel: db_trace_self_wrapper() at  
db_trace_self_wrapper+0x2a
Sep 28 19:47:46  kernel: _witness_debugger() at _witness_debugger+0x2e
Sep 28 19:47:46  kernel: witness_checkorder() at witness_checkorder 
+0x81e
Sep 28 19:47:46  kernel: __lockmgr_args() at __lockmgr_args+0xd03
Sep 28 19:47:46  kernel: vop_stdlock() at vop_stdlock+0x39
Sep 28 19:47:46  kernel: VOP_LOCK1_APV() at VOP_LOCK1_APV+0x9b
Sep 28 19:47:46  kernel: _vn_lock() at _vn_lock+0x57
Sep 28 19:47:46  kernel: ffs_flushfiles() at ffs_flushfiles+0xc5
Sep 28 19:47:46  kernel: softdep_flushfiles() at softdep_flushfiles+0x63
Sep 28 19:47:46  kernel: ffs_unmount() at ffs_unmount+0x2e1
Sep 28 19:47:46  kernel: dounmount() at dounmount+0x2e6
Sep 28 19:47:46  kernel: unmount() at unmount+0x27e
Sep 28 19:47:46  kernel: syscall() at syscall+0x1d0
Sep 28 19:47:46  kernel: Xfast_syscall() at Xfast_syscall+0xe1
Sep 28 19:47:46  kernel: --- syscall (22, FreeBSD ELF64, unmount), rip  
= 0x8006a09bc, rsp = 0x7fffffffe3b8, rbp = 0 ---

FreeBSD  8.0-RC1 FreeBSD 8.0-RC1 #0: Fri Sep 25 16:55:06 CEST 2009      
root@:/usr/obj/usr/src/sys/DEBUG  amd64

I'm running it on VMWare Fussion, but it shouldn't matter.

The system has two disks, one of them just a root partition and the  
other one has two filesystems, one for /usr/src and the other for /usr/ 
obj

How to reproduce?

Right after boot, I have mounted /usr/src and /usr/obj.

Unmounting /usr/obj has given this LOR.

I can reproduce it easily, please let me know if I can do anything else.





Borja.




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