From 06c85cef9d1d8a709730843fe9dbef7d341f79fc Mon Sep 17 00:00:00 2001
From: Doug Rabson <dfr@FreeBSD.org>
Date: Fri, 9 May 2008 10:34:23 +0000
Subject: [PATCH] When blocking on an F_FLOCK style lock request which is
 upgrading a shared lock to exclusive, drop the shared lock before deadlock
 detection.

MFC after: 2 days
---
 sys/kern/kern_lockf.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/sys/kern/kern_lockf.c b/sys/kern/kern_lockf.c
index 045a3ba2f76..8cab502a6f8 100644
--- a/sys/kern/kern_lockf.c
+++ b/sys/kern/kern_lockf.c
@@ -1369,6 +1369,18 @@ lf_setlock(struct lockf *state, struct lockf_entry *lock, struct vnode *vp,
 			goto out;
 		}
 
+		/*
+		 * For flock type locks, we must first remove
+		 * any shared locks that we hold before we sleep
+		 * waiting for an exclusive lock.
+		 */
+		if ((lock->lf_flags & F_FLOCK) &&
+		    lock->lf_type == F_WRLCK) {
+			lock->lf_type = F_UNLCK;
+			lf_activate_lock(state, lock);
+			lock->lf_type = F_WRLCK;
+		}
+
 		/*
 		 * We are blocked. Create edges to each blocking lock,
 		 * checking for deadlock using the owner graph. For
@@ -1388,17 +1400,6 @@ lf_setlock(struct lockf *state, struct lockf_entry *lock, struct vnode *vp,
 			goto out;
 		}
 
-		/*
-		 * For flock type locks, we must first remove
-		 * any shared locks that we hold before we sleep
-		 * waiting for an exclusive lock.
-		 */
-		if ((lock->lf_flags & F_FLOCK) &&
-		    lock->lf_type == F_WRLCK) {
-			lock->lf_type = F_UNLCK;
-			lf_activate_lock(state, lock);
-			lock->lf_type = F_WRLCK;
-		}
 		/*
 		 * We have added edges to everything that blocks
 		 * us. Sleep until they all go away.