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diff --git a/sys/fs/unionfs/union_vfsops.c b/sys/fs/unionfs/union_vfsops.c
--- a/sys/fs/unionfs/union_vfsops.c
+++ b/sys/fs/unionfs/union_vfsops.c
@@ -73,6 +73,8 @@
{
struct vnode *lowerrootvp;
struct vnode *upperrootvp;
+ struct vnode *lvp1;
+ struct vnode *lvp2;
struct unionfs_mount *ump;
char *target;
char *tmp;
@@ -276,11 +278,32 @@
*/
VOP_UNLOCK(ump->um_uppervp);
+ /*
+ * Detect common cases in which constructing a unionfs hierarchy
+ * would produce deadlock (or failed locking assertions) upon
+ * use of the resulting unionfs vnodes. This typically happens
+ * when the requested upper and lower filesytems (which themselves
+ * may be unionfs instances and/or nullfs aliases) end up resolving
+ * to the same base-layer files. Note that this is not meant to be
+ * an exhaustive check of all possible deadlock-producing scenarios.
+ */
+ lvp1 = lvp2 = NULL;
+ VOP_GETLOWVNODE(ump->um_lowervp, &lvp1, FREAD);
+ VOP_GETLOWVNODE(ump->um_uppervp, &lvp2, FREAD);
+ if (lvp1 != NULL && lvp1 == lvp2)
+ error = EDEADLK;
+ if (lvp1 != NULL)
+ vrele(lvp1);
+ if (lvp2 != NULL)
+ vrele(lvp2);
+
/*
* Get the unionfs root vnode.
*/
- error = unionfs_nodeget(mp, ump->um_uppervp, ump->um_lowervp,
- NULL, &(ump->um_rootvp), NULL);
+ if (error == 0) {
+ error = unionfs_nodeget(mp, ump->um_uppervp, ump->um_lowervp,
+ NULL, &(ump->um_rootvp), NULL);
+ }
if (error != 0) {
vrele(upperrootvp);
free(ump, M_UNIONFSMNT);
diff --git a/sys/fs/unionfs/union_vnops.c b/sys/fs/unionfs/union_vnops.c
--- a/sys/fs/unionfs/union_vnops.c
+++ b/sys/fs/unionfs/union_vnops.c
@@ -2105,6 +2105,51 @@
return (error);
}
+static int
+unionfs_getlowvnode(struct vop_getlowvnode_args *ap)
+{
+ struct unionfs_node *unp;
+ struct vnode *vp, *basevp;
+
+ vp = ap->a_vp;
+ VI_LOCK(vp);
+ unp = VTOUNIONFS(vp);
+ if (unp == NULL) {
+ VI_UNLOCK(vp);
+ return (EBADF);
+ }
+
+ if (ap->a_flags & FWRITE) {
+ basevp = unp->un_uppervp;
+ /*
+ * If we're being asked to resolve a write and an upper
+ * vnode is not present, tell the caller that our unionfs
+ * vnode will resolve the write so that we can do the
+ * copy-up if/when the write eventually happens.
+ * We could proactively do the copy-up here, but that would
+ * require additional locking as well as the addition of
+ * a 'cred' argument to VOP_GETLOWVNODE(). Such a copy-up
+ * could also ultimately be redundant or unnecessary
+ * depending upon what the caller proceeds to do.
+ */
+ if (basevp == NULL) {
+ VI_UNLOCK(vp);
+ return (vop_stdgetlowvnode(ap));
+ }
+ } else {
+ basevp = (unp->un_uppervp != NULL) ?
+ unp->un_uppervp : unp->un_lowervp;
+ }
+
+ VNASSERT(basevp != NULL, vp, ("%s: no upper/lower vnode", __func__));
+
+ vholdnz(basevp);
+ VI_UNLOCK(vp);
+ VOP_GETLOWVNODE(basevp, ap->a_vplp, ap->a_flags);
+ vdrop(basevp);
+ return (0);
+}
+
static int
unionfs_inactive(struct vop_inactive_args *ap)
{
@@ -3000,6 +3045,7 @@
.vop_getattr = unionfs_getattr,
.vop_getextattr = unionfs_getextattr,
.vop_getwritemount = unionfs_getwritemount,
+ .vop_getlowvnode = unionfs_getlowvnode,
.vop_inactive = unionfs_inactive,
.vop_need_inactive = vop_stdneed_inactive,
.vop_islocked = vop_stdislocked,
@@ -3039,5 +3085,6 @@
.vop_unp_bind = unionfs_unp_bind,
.vop_unp_connect = unionfs_unp_connect,
.vop_unp_detach = unionfs_unp_detach,
+ .vop_copy_file_range = vop_stdcopy_file_range,
};
VFS_VOP_VECTOR_REGISTER(unionfs_vnodeops);
diff --git a/sys/kern/vfs_default.c b/sys/kern/vfs_default.c
--- a/sys/kern/vfs_default.c
+++ b/sys/kern/vfs_default.c
@@ -77,13 +77,11 @@
static int vop_stdis_text(struct vop_is_text_args *ap);
static int vop_stdunset_text(struct vop_unset_text_args *ap);
static int vop_stdadd_writecount(struct vop_add_writecount_args *ap);
-static int vop_stdcopy_file_range(struct vop_copy_file_range_args *ap);
static int vop_stdfdatasync(struct vop_fdatasync_args *ap);
static int vop_stdgetpages_async(struct vop_getpages_async_args *ap);
static int vop_stdread_pgcache(struct vop_read_pgcache_args *ap);
static int vop_stdstat(struct vop_stat_args *ap);
static int vop_stdvput_pair(struct vop_vput_pair_args *ap);
-static int vop_stdgetlowvnode(struct vop_getlowvnode_args *ap);
/*
* This vnode table stores what we want to do if the filesystem doesn't
@@ -1426,7 +1424,7 @@
return (0);
}
-static int
+int
vop_stdcopy_file_range(struct vop_copy_file_range_args *ap)
{
int error;
@@ -1636,7 +1634,7 @@
return (0);
}
-static int
+int
vop_stdgetlowvnode(struct vop_getlowvnode_args *ap)
{
vref(ap->a_vp);
diff --git a/sys/kern/vnode_if.src b/sys/kern/vnode_if.src
--- a/sys/kern/vnode_if.src
+++ b/sys/kern/vnode_if.src
@@ -469,7 +469,7 @@
OUT struct mount **mpp;
};
-%% getwritevnode vp = = =
+%% getlowvnode vp = = =
vop_getlowvnode {
IN struct vnode *vp;
diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -906,6 +906,8 @@
int vop_stdunp_connect(struct vop_unp_connect_args *ap);
int vop_stdunp_detach(struct vop_unp_detach_args *ap);
int vop_stdadd_writecount_nomsync(struct vop_add_writecount_args *ap);
+int vop_stdcopy_file_range(struct vop_copy_file_range_args *ap);
+int vop_stdgetlowvnode(struct vop_getlowvnode_args *ap);
int vop_eopnotsupp(struct vop_generic_args *ap);
int vop_ebadf(struct vop_generic_args *ap);
int vop_einval(struct vop_generic_args *ap);

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