LOR: vfs_mount.c (ufs) / msdosfs_vfsops.c (devfs)
Attilio Rao
attilio at freebsd.org
Mon Feb 8 15:01:59 UTC 2010
2010/2/8 Kostik Belousov <kostikbel at gmail.com>:
> On Mon, Feb 08, 2010 at 09:00:44AM -0500, John Baldwin wrote:
>> On Sunday 07 February 2010 11:00:32 am Bruce Cran wrote:
>> > Running -CURRENT from today, I unmounted the msdosfs filesystem on my
>> > phone and got the following LOR:
>> >
>> > lock order reversal:
>> > 1st 0xffffff00c51279f8 ufs (ufs) @ /usr/src/sys/kern/vfs_mount.c:1204
>> > 2nd 0xffffff010b892278 devfs (devfs) @
>> > /usr/src/sys/modules/msdosfs/../../fs/msdosfs/msdosfs_vfsops.c:944
>> > KDB: stack backtrace:
>> > db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
>> > _witness_debugger() at witness_debugger+0x2e
>> > witness_checkorder() at witness_checkorder+0x81e
>> > __lockmgr_args() at __lockmgr_args+0xd11
>> > vop_stdlock() at vop_stdlock+0x39
>> > VOP_LOCK1_APV() VOP_LOCK1_APV+0x9b
>> > _vn_lock() at _vn_lock+0x47
>> > msdosfs_sync() at msdosfs_sync+0x227
>> > dounmount() at dounmount+0x2ca
>> > unmount() at unmount+0x216
>> > syscall() at syscall+0x2a2
>> > Xfast_syscall() at Xfast_syscall+0xe1
>> > --- syscall (22, FreeBSD ELF64, unmount), rip = 0x8006a1e3c, rsp =
>> > 0x7fffffffe3a8, rbp = 0x800c08010 ---
>>
>> This is due to holding a lock on the coveredvp vnode for most of unmount(2).
>> Probably it should not be held for all of that. Perhaps it is safe to just
>> keep the vnode referenced instead, or could the handling for coveredvp just
>> move to the end of the function where it is now vput?
>
> Among other things, holding vnode lock on covered vnode prevents parallel
> unmounts of the same mount point.
Uhm, I think that this should be hanlded by MNTK_UNMOUNT already (and
thus stopping forced unmounts too).
Attilio
--
Peace can only be achieved by understanding - A. Einstein
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