From 9095719e2b05d6e1673b755809128a6ad3ea1388 Mon Sep 17 00:00:00 2001 From: KATO Takenori Date: Tue, 15 Apr 1997 12:56:57 +0000 Subject: [PATCH] Quick-hack to avoid `lock against myself' panic. It is not the real fix! The ufs_link() assumes that vnode is not unlocked and tries to lock it in certain case. Because union_link calls VOP_LINK after locking vnode, vn_lock in ufs_link causes above panic. Currently, I don't know the real fix for a locking violation in union_link, but I think it is important to avoid panic. A vnode is unlocked before calling VOP_LINK and is locked after it if the vnode is not union fs. Even though panic went away, the process that access the union fs in which link was made will hang-up. Hang-up can be easily reproduced by following operation: mount -t union a b cd b ln foo bar ls --- sys/fs/unionfs/union_vnops.c | 17 +++++++++++++++-- sys/miscfs/union/union_vnops.c | 17 +++++++++++++++-- 2 files changed, 30 insertions(+), 4 deletions(-) diff --git a/sys/fs/unionfs/union_vnops.c b/sys/fs/unionfs/union_vnops.c index e05372f5b663..4b70f2c5a4bd 100644 --- a/sys/fs/unionfs/union_vnops.c +++ b/sys/fs/unionfs/union_vnops.c @@ -35,7 +35,7 @@ * SUCH DAMAGE. * * @(#)union_vnops.c 8.32 (Berkeley) 6/23/95 - * $Id: union_vnops.c,v 1.22 1997/04/13 13:12:12 kato Exp $ + * $Id: union_vnops.c,v 1.23 1997/04/14 05:13:55 kato Exp $ */ #include @@ -1058,6 +1058,7 @@ union_link(ap) struct union_node *un; struct vnode *vp; struct vnode *tdvp; + int isvnunlocked = 0; un = VTOUNION(ap->a_tdvp); @@ -1096,7 +1097,19 @@ union_link(ap) un->un_flags |= UN_KLOCK; vput(ap->a_tdvp); - return (VOP_LINK(vp, tdvp, cnp)); + /* + * XXX -- This is a quick-hack to avoid panic. Problem still remains! + * The process which access the union filesystem will be hang-up after + * making link in the union fs. + */ + if (VOP_ISLOCKED(tdvp) && (tdvp->v_op != union_vnodeop_p)) { + isvnunlocked = 1; + VOP_UNLOCK(tdvp, 0, p); + } + error = VOP_LINK(vp, tdvp, cnp); + if (isvnunlocked) + vn_lock(tdvp, LK_EXCLUSIVE | LK_RETRY, p); + return error; } int diff --git a/sys/miscfs/union/union_vnops.c b/sys/miscfs/union/union_vnops.c index e05372f5b663..4b70f2c5a4bd 100644 --- a/sys/miscfs/union/union_vnops.c +++ b/sys/miscfs/union/union_vnops.c @@ -35,7 +35,7 @@ * SUCH DAMAGE. * * @(#)union_vnops.c 8.32 (Berkeley) 6/23/95 - * $Id: union_vnops.c,v 1.22 1997/04/13 13:12:12 kato Exp $ + * $Id: union_vnops.c,v 1.23 1997/04/14 05:13:55 kato Exp $ */ #include @@ -1058,6 +1058,7 @@ union_link(ap) struct union_node *un; struct vnode *vp; struct vnode *tdvp; + int isvnunlocked = 0; un = VTOUNION(ap->a_tdvp); @@ -1096,7 +1097,19 @@ union_link(ap) un->un_flags |= UN_KLOCK; vput(ap->a_tdvp); - return (VOP_LINK(vp, tdvp, cnp)); + /* + * XXX -- This is a quick-hack to avoid panic. Problem still remains! + * The process which access the union filesystem will be hang-up after + * making link in the union fs. + */ + if (VOP_ISLOCKED(tdvp) && (tdvp->v_op != union_vnodeop_p)) { + isvnunlocked = 1; + VOP_UNLOCK(tdvp, 0, p); + } + error = VOP_LINK(vp, tdvp, cnp); + if (isvnunlocked) + vn_lock(tdvp, LK_EXCLUSIVE | LK_RETRY, p); + return error; } int