2010/2/8 Kostik Belousov <kostikbel_at_gmail.com>: > On Mon, Feb 08, 2010 at 04:06:56PM +0100, Attilio Rao wrote: >> 2010/2/8 Attilio Rao <attilio_at_freebsd.org>: >> > 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) _at_ /usr/src/sys/kern/vfs_mount.c:1204 >> >>> > 2nd 0xffffff010b892278 devfs (devfs) _at_ >> >>> > /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). >> >> In other words probabilly keeping coveredvnode held until MNTK_UNMOUNT >> and then refcounting it should be fine. > > Actually, the coveredvp then might be reclaimed ? Failed unmount then > cannot recover. I thought on domount() we did holdcount the coveredvp for the time being? If we don't, maybe we should. Attilio -- Peace can only be achieved by understanding - A. EinsteinReceived on Mon Feb 08 2010 - 14:40:31 UTC
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