Date: Mon, 8 Feb 2010 17:08:18 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Attilio Rao <attilio@freebsd.org> 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: <20100208150818.GL9991@deviant.kiev.zoral.com.ua> In-Reply-To: <3bbf2fe11002080706k11275a9evbf8a7fa1b14b447f@mail.gmail.com> 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>
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--Jbyekxk18hnEXT0m Content-Type: text/plain; charset=koi8-r Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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: > >>> > =9A1st 0xffffff00c51279f8 ufs (ufs) @ /usr/src/sys/kern/vfs_mount.c= :1204 > >>> > =9A2nd 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 =3D 0x8006a1e3c, rsp = =3D > >>> > 0x7fffffffe3a8, rbp =3D 0x800c08010 --- > >>> > >>> This is due to holding a lock on the coveredvp vnode for most of unmo= unt(2). > >>> Probably it should not be held for all of that. =9APerhaps it is safe= to just > >>> keep the vnode referenced instead, or could the handling for coveredv= p just > >>> move to the end of the function where it is now vput? > >> > >> Among other things, holding vnode lock on covered vnode prevents paral= lel > >> unmounts of the same mount point. > > > > Uhm, I think that this should be hanlded by MNTK_UNMOUNT already (and > > thus stopping forced unmounts too). >=20 > 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. --Jbyekxk18hnEXT0m Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD) iEYEARECAAYFAktwKOIACgkQC3+MBN1Mb4gN8ACfbyEy0RlFkxwuUEhLTVLcLB8W 6WYAn2amrTTHMvBTD2Gd1YD21OnqwDsN =tT1w -----END PGP SIGNATURE----- --Jbyekxk18hnEXT0m--
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