From d0a724c5ea93e561bccfbe91219710009bc553e4 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Mon, 1 Aug 2011 19:07:03 +0000
Subject: [PATCH] Fix the LK_NOSHARE lockmgr flag interaction with LK_UPGRADE
 and LK_DOWNGRADE lock ops. Namely, the ops should be NOP since LK_NOSHARE
 locks are always exclusive.

Reported by:	rmacklem
Reviewed by:	attilio
Tested by:	pho
Approved by:	re (kensmith)
MFC after:	1 week
---
 sys/kern/kern_lock.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/sys/kern/kern_lock.c b/sys/kern/kern_lock.c
index 8e5546ee307..73118726e3a 100644
--- a/sys/kern/kern_lock.c
+++ b/sys/kern/kern_lock.c
@@ -477,8 +477,18 @@ __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
 		return (0);
 	}
 
-	if (op == LK_SHARED && (lk->lock_object.lo_flags & LK_NOSHARE))
-		op = LK_EXCLUSIVE;
+	if (lk->lock_object.lo_flags & LK_NOSHARE) {
+		switch (op) {
+		case LK_SHARED:
+			op = LK_EXCLUSIVE;
+			break;
+		case LK_UPGRADE:
+		case LK_DOWNGRADE:
+			_lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED,
+			    file, line);
+			return (0);
+		}
+	}
 
 	wakeup_swapper = 0;
 	switch (op) {