D37458.id114044.diff
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	diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
	--- a/sys/kern/vfs_lookup.c
	+++ b/sys/kern/vfs_lookup.c
	@@ -1265,14 +1265,28 @@
	crosslock = (dp->v_vflag & VV_CROSSLOCK) != 0;
	crosslkflags = compute_cn_lkflags(mp, cnp->cn_lkflags,
	cnp->cn_flags);
	- if (__predict_false(crosslock) &&
	- (crosslkflags & LK_EXCLUSIVE) != 0 &&
	- VOP_ISLOCKED(dp) != LK_EXCLUSIVE) {
	- vn_lock(dp, LK_UPGRADE \| LK_RETRY);
	- if (VN_IS_DOOMED(dp)) {
	- error = ENOENT;
	- goto bad2;
	- }
	+ if (__predict_false(crosslock)) {
	+ /*
	+ * We are going to be holding the vnode lock, which
	+ * in this case is shared by the root vnode of the
	+ * filesystem mounted at mp, across the call to
	+ * VFS_ROOT(). Make the situation clear to the
	+ * filesystem by passing LK_CANRECURSE if the
	+ * lock is held exclusive, or by clearinng
	+ * LK_NODDLKTREAT to allow recursion on the shared
	+ * lock in the presence of an exclusive waiter.
	+ */
	+ if (VOP_ISLOCKED(dp) == LK_EXCLUSIVE) {
	+ crosslkflags &= ~LK_SHARED;
	+ crosslkflags \|= LK_EXCLUSIVE \| LK_CANRECURSE;
	+ } else if ((crosslkflags & LK_EXCLUSIVE) != 0) {
	+ vn_lock(dp, LK_UPGRADE \| LK_RETRY);
	+ if (VN_IS_DOOMED(dp)) {
	+ error = ENOENT;
	+ goto bad2;
	+ }
	+ } else
	+ crosslkflags &= ~LK_NODDLKTREAT;
	}
	if (vfs_busy(mp, 0) != 0)
	continue;