From owner-freebsd-current@FreeBSD.ORG Tue Dec 12 10:22:15 2006 Return-Path: X-Original-To: freebsd-current@freebsd.org Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 19A3016A49E; Tue, 12 Dec 2006 10:22:15 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from fw.zoral.com.ua (fw.zoral.com.ua [213.186.206.134]) by mx1.FreeBSD.org (Postfix) with ESMTP id 0487C43EEB; Tue, 12 Dec 2006 10:18:00 +0000 (GMT) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (root@deviant.kiev.zoral.com.ua [10.1.1.148]) by fw.zoral.com.ua (8.13.4/8.13.4) with ESMTP id kBCAJ4ap092429 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 12 Dec 2006 12:19:04 +0200 (EET) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (kostik@localhost [127.0.0.1]) by deviant.kiev.zoral.com.ua (8.13.8/8.13.8) with ESMTP id kBCAJ4Gg073302; Tue, 12 Dec 2006 12:19:04 +0200 (EET) (envelope-from kostikbel@gmail.com) Received: (from kostik@localhost) by deviant.kiev.zoral.com.ua (8.13.8/8.13.8/Submit) id kBCAJ3md073301; Tue, 12 Dec 2006 12:19:03 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: deviant.kiev.zoral.com.ua: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 12 Dec 2006 12:19:03 +0200 From: Kostik Belousov To: Suleiman Souhlal Message-ID: <20061212101903.GF311@deviant.kiev.zoral.com.ua> References: <456950AF.3090308@sh.cvut.cz> <20061127092146.GA69556@deviant.kiev.zoral.com.ua> <457E6C06.1020405@FreeBSD.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="J4XPiPrVK1ev6Sgr" Content-Disposition: inline In-Reply-To: <457E6C06.1020405@FreeBSD.org> User-Agent: Mutt/1.4.2.2i X-Virus-Scanned: ClamAV version 0.88.4, clamav-milter version 0.88.4 on fw.zoral.com.ua X-Virus-Status: Clean X-Spam-Status: No, score=1.4 required=5.0 tests=SPF_NEUTRAL, UNPARSEABLE_RELAY autolearn=no version=3.1.4 X-Spam-Level: * X-Spam-Checker-Version: SpamAssassin 3.1.4 (2006-07-25) on fw.zoral.com.ua X-Mailman-Approved-At: Tue, 12 Dec 2006 13:10:27 +0000 Cc: freebsd-stable@freebsd.org, V??clav Haisman , tegge@freebsd.org, bde@freebsd.org, freebsd-current@freebsd.org Subject: Re: kqueue LOR X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 12 Dec 2006 10:22:15 -0000 --J4XPiPrVK1ev6Sgr Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Dec 12, 2006 at 12:44:54AM -0800, Suleiman Souhlal wrote: > Kostik Belousov wrote: > >On Sun, Nov 26, 2006 at 09:30:39AM +0100, V??clav Haisman wrote: > > > >>Hi, > >>the attached lor.txt contains LOR I got this yesterday. It is FreeBSD 6= .1 > >>with relatively recent kernel, from last week or so. > >> > >>-- > >>VH > > > > > >>+lock order reversal: > >>+ 1st 0xc537f300 kqueue (kqueue) @ /usr/src/sys/kern/kern_event.c:1547 > >>+ 2nd 0xc45c22dc struct mount mtx (struct mount mtx) @=20 > >>/usr/src/sys/ufs/ufs/ufs_vnops.c:138 > >>+KDB: stack backtrace: > >>+kdb_backtrace(c07f9879,c45c22dc,c07fd31c,c07fd31c,c080c7b2,...) at=20 > >>kdb_backtrace+0x2f > >>+witness_checkorder(c45c22dc,9,c080c7b2,8a,c07fc6bd,...) at=20 > >>witness_checkorder+0x5fe > >>+_mtx_lock_flags(c45c22dc,0,c080c7b2,8a,e790ba20,...) at=20 > >>_mtx_lock_flags+0x32 > >>+ufs_itimes(c47a0dd0,c47a0e90,e790ba78,c060e1cc,c47a0dd0,...) at=20 > >>ufs_itimes+0x6c > >>+ufs_getattr(e790ba54,e790baec,c0622af6,c0896f40,e790ba54,...) at=20 > >>ufs_getattr+0x20 > >>+VOP_GETATTR_APV(c0896f40,e790ba54,c08a5760,c47a0dd0,e790ba74,...) at= =20 > >>VOP_GETATTR_APV+0x3a > >>+filt_vfsread(c4cf261c,6,c07f445e,60b,0,...) at filt_vfsread+0x75 > >>+knote(c4f57114,6,1,1f30c2af,1f30c2af,...) at knote+0x75 > >>+VOP_WRITE_APV(c0896f40,e790bbec,c47a0dd0,227,e790bcb4,...) at=20 > >>VOP_WRITE_APV+0x148 > >>+vn_write(c45d5120,e790bcb4,c5802a00,0,c4b73a80,...) at vn_write+0x201 > >>+dofilewrite(c4b73a80,1b,c45d5120,e790bcb4,ffffffff,...) at=20 > >>dofilewrite+0x84 > >>+kern_writev(c4b73a80,1b,e790bcb4,8220c71,0,...) at kern_writev+0x65 > >>+write(c4b73a80,e790bd04,c,c07d899c,3,...) at write+0x4f > >>+syscall(3b,3b,bfbf003b,0,bfbfeae4,...) at syscall+0x295 > >>+Xint0x80_syscall() at Xint0x80_syscall+0x1f > >>+--- syscall (4, FreeBSD ELF32, write), eip =3D 0x2831d727, esp =3D=20 > >>0xbfbfea1c, ebp =3D 0xbfbfea48 --- > > > > > >Thank you for the report. The LOR is caused by my commit into > >sys/ufs/ufs/ufs_vnops.c, rev. 1.280. >=20 > Is the mount lock really required, if all we're doing is a single read of= a=20 > single word (mnt_kern_flags) (v_mount should be read-only for the whole= =20 > lifetime of the vnode, I believe)? After all, reads of a single word are= =20 > atomic on all our supported architectures. > The only situation I see where there MIGHT be problems are forced unmount= s,=20 > but I think there are bigger issues with those. > Sorry for noticing this email only now. The problem is real with snapshotting. Ignoring MNTK_SUSPEND/MNTK_SUSPENDED flags (in particular, reading stale value of mnt_kern_flag) while setting IN_MODIFIED caused deadlock at ufs vnode inactivation time. This was the big trouble with nfsd and snapshots. As such, I think that precise value of mmnt_kern_flag is critical there, and mount interlock is needed. Practically speaking, I agree with claim that reading of m_k_f is surrounded by enough locked operations that would make sure that the read value is not stale. But there is no such guarantee on future/non-i386 arches, isn't it ? As a side note, mount interlock scope could be reduced there. Index: ufs/ufs/ufs_vnops.c =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D RCS file: /usr/local/arch/ncvs/src/sys/ufs/ufs/ufs_vnops.c,v retrieving revision 1.283 diff -u -r1.283 ufs_vnops.c --- ufs/ufs/ufs_vnops.c 6 Nov 2006 13:42:09 -0000 1.283 +++ ufs/ufs/ufs_vnops.c 12 Dec 2006 10:18:04 -0000 @@ -133,19 +134,19 @@ { struct inode *ip; struct timespec ts; - int mnt_locked; =20 ip =3D VTOI(vp); - mnt_locked =3D 0; if ((vp->v_mount->mnt_flag & MNT_RDONLY) !=3D 0) { VI_LOCK(vp); goto out; } MNT_ILOCK(vp->v_mount); /* For reading of mnt_kern_flags. */ - mnt_locked =3D 1; VI_LOCK(vp); - if ((ip->i_flag & (IN_ACCESS | IN_CHANGE | IN_UPDATE)) =3D=3D 0) - goto out_unl; + if ((ip->i_flag & (IN_ACCESS | IN_CHANGE | IN_UPDATE)) =3D=3D 0) { + MNT_IUNLOCK(vp->v_mount); + VI_UNLOCK(vp); + return; + } =20 if ((vp->v_type =3D=3D VBLK || vp->v_type =3D=3D VCHR) && !DOINGSOFTDEP(v= p)) ip->i_flag |=3D IN_LAZYMOD; @@ -155,6 +156,7 @@ ip->i_flag |=3D IN_MODIFIED; else if (ip->i_flag & IN_ACCESS) ip->i_flag |=3D IN_LAZYACCESS; + MNT_IUNLOCK(vp->v_mount); vfs_timestamp(&ts); if (ip->i_flag & IN_ACCESS) { DIP_SET(ip, i_atime, ts.tv_sec); @@ -172,10 +174,7 @@ =20 out: ip->i_flag &=3D ~(IN_ACCESS | IN_CHANGE | IN_UPDATE); - out_unl: VI_UNLOCK(vp); - if (mnt_locked) - MNT_IUNLOCK(vp->v_mount); } =20 /* --J4XPiPrVK1ev6Sgr Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (FreeBSD) iD8DBQFFfoIWC3+MBN1Mb4gRAmA8AKCrbt+mT1HCNj3VnFFQVu+fb2JzZQCcCr0L n4DVdlGDbEkZAwaaBZhEFo8= =7yaQ -----END PGP SIGNATURE----- --J4XPiPrVK1ev6Sgr--