Date: Mon, 8 Feb 2010 17:29:44 +0100 From: Attilio Rao <attilio@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: bzeeb+freebsd+lor@zabbadoz.net, Bruce Cran <bruce@cran.org.uk>, freebsd-current@freebsd.org Subject: Re: LOR: vfs_mount.c (ufs) / msdosfs_vfsops.c (devfs) Message-ID: <3bbf2fe11002080829l4d5bb55ue82e3ce5f65f2ae2@mail.gmail.com> In-Reply-To: <20100208154158.GM9991@deviant.kiev.zoral.com.ua> References: <20100207160031.GA27434@muon.cran.org.uk> <201002080900.44745.jhb@freebsd.org> <20100208145354.GJ9991@deviant.kiev.zoral.com.ua> <3bbf2fe11002080701u35a3e419ke562735f4f00ce97@mail.gmail.com> <3bbf2fe11002080706k11275a9evbf8a7fa1b14b447f@mail.gmail.com> <20100208150818.GL9991@deviant.kiev.zoral.com.ua> <3bbf2fe11002080740q1da560c8r8c8d92a1053d021b@mail.gmail.com> <20100208154158.GM9991@deviant.kiev.zoral.com.ua>
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2010/2/8 Kostik Belousov <kostikbel@gmail.com>: > On Mon, Feb 08, 2010 at 04:40:29PM +0100, Attilio Rao wrote: >> 2010/2/8 Kostik Belousov <kostikbel@gmail.com>: >> > On Mon, Feb 08, 2010 at 04:06:56PM +0100, Attilio Rao wrote: >> >> 2010/2/8 Attilio Rao <attilio@freebsd.org>: >> >> > 2010/2/8 Kostik Belousov <kostikbel@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). >> >> >> >> 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. > Hold or ref does not prevent reclaim. Oh right, I readed recycle. Attilio -- Peace can only be achieved by understanding - A. Einstein
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