Date: Fri, 3 Feb 2006 16:40:34 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: freebsd-hackers@freebsd.org Subject: [possible patch] fdescfs vop_lookup and parent vnode locking Message-ID: <c781d7f30602030640i31762e4bk8aa1234abc099613@mail.gmail.com>
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Is it correct that filesystem-specific vop_lookup is expected to
take the directory vnode (dvp) locked, and shall return with dvp locked ?
vnode_if.src specifies this behaviour as dependent on the flags in the cnp
arguments. My reading of the sources suggest that the statement in the firs=
t
sentence is true, and note from vnode_if.src applies to
sys/kern/vfs_lookup.c:lookup() procedure itself.
If it is true, the fdescfs break this rule, dropping the lock on the dvp. S=
ee
sys/fs/fdescfs/fdesc_vnops.c, line 196. As result, having fdescfs mounted,
most accesses to files on it cause warning from the lockmgr,
lockmgr: thread XXX unlocking unheld lock
I did some testing with the following patch
Index: sys/fs/fdescfs/fdesc_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/fs/fdescfs/fdesc_vnops.c,v
retrieving revision 1.100
diff -u -r1.100 fdesc_vnops.c
--- sys/fs/fdescfs/fdesc_vnops.c=0910 Aug 2005 07:08:14 -0000=091.100
+++ sys/fs/fdescfs/fdesc_vnops.c=093 Feb 2006 14:35:11 -0000
@@ -193,11 +193,9 @@
=09=09goto bad;
=09}
-=09VOP_UNLOCK(dvp, 0, td);
=09if (cnp->cn_namelen =3D=3D 1 && *pname =3D=3D '.') {
=09=09*vpp =3D dvp;
=09=09VREF(dvp);
-=09=09vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY, td);
=09=09return (0);
=09}
@@ -228,12 +226,12 @@
=09if (error)
=09=09goto bad;
=09VTOFDESC(fvp)->fd_fd =3D fd;
-=09vn_lock(fvp, LK_EXCLUSIVE | LK_RETRY, td);
+=09if (fvp !=3D dvp)
+=09=09vn_lock(fvp, LK_EXCLUSIVE | LK_RETRY, td);
=09*vpp =3D fvp;
=09return (0);
bad:
-=09vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY, td);
=09*vpp =3D NULL;
=09return (error);
}
and do not see the warnings anymore. The system does not deadlock.
What do you think about the problem ?
Best regards,
Kostik Belousov
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