Old LOR between devfs & devfsmount resurfacing?
attilio at freebsd.org
Thu Feb 7 10:16:11 UTC 2008
2008/2/7, Kostik Belousov <kostikbel at gmail.com>:
> On Wed, Feb 06, 2008 at 11:11:06AM -0800, Marcel Moolenaar wrote:
> > All,
> > I just ran into the following LOR after upgrading my PowerPC box:
> > lock order reversal:
> > 1st 0xdbee94 devfs (devfs) @ /nfs/freebsd/8.x/src/sys/kern/
> > vfs_subr.c:2061
> > 2nd 0xdfb014 devfsmount (devfsmount) @ /nfs/freebsd/8.x/src/sys/fs/
> > devfs/devfs_vnops.c:201
> > KDB: stack backtrace:
> > 0xdc0febc8: at kdb_backtrace+0x4c
> > 0xdc0febd8: at witness_checkorder+0x704
> > 0xdc0fec28: at _sx_xlock+0x8c
> > 0xdc0fec48: at devfs_allocv+0x138
> > 0xdc0fec88: at devfs_root+0x5c
> > 0xdc0fecb8: at set_rootvnode+0x44
> > 0xdc0fece8: at vfs_mountroot+0x344
> > 0xdc0fed48: at start_init+0x88
> > 0xdc0feda8: at fork_exit+0xb4
> > 0xdc0fedc8: at fork_trampoline+0xc
> > KDB: enter: witness_checkorder
> > [thread pid 1 tid 100001 ]
> > Stopped at 0x28ee68: addi r0, r0, 0x0
> > It seems that this is a LOR reported in 2006 and fixed
> > in 2006 as well. Do other people see this too, or should
> > I suspect my sources?
> I believe this is a false positive, caused by the way the witness works.
> Attilio recently added the witness support for the lockmgr, that caused
> this and at least two more LORs to be printed on startup.
> Correct lock order is devfs vnode -> devfs mount sx lock. When
> allocating new devfs vnode, see devfs_allocv(), the newly created
> vnode is locked while devfs mount lock already held (see line 250 of
> fs/devfs/devfs_vnops.c). Nonetheless, this cannot cause deadlock since
> no other thread can find the new vnode, and thus perform the other lock
> order for this vnode lock.
> The fix is to shut the witness in this particular case. Attilio, how to
> do this ?
Just add LK_NOWITNESS for one of the lock involved in the lockinit().
Peace can only be achieved by understanding - A. Einstein
More information about the freebsd-current