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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Fri, 14 Aug 2009 10:59:17 +0000 (UTC)
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Subject: svn commit: r196205 - head/sys/nfsclient
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Author: kib
Date: Fri Aug 14 10:59:17 2009
New Revision: 196205
URL: http://svn.freebsd.org/changeset/base/196205

Log:
  In nfs_upgrade_vnlock(), assert that the vnode is locked. It is for all
  pathes, as far as I see and testing seems to confirm it. Comparision of
  old_lock with LK_SHARED make sense only if vnode is locked by current
  thread.
  
  When downgrading, pass LK_RETRY to the vn_lock(), since otherwise
  vn_lock() unlocks the doomed vnode, causing extra unlock.
  
  Reported and tested by:	pho
  Approved by:	re (rwatson)
  MFC after:	3 weeks

Modified:
  head/sys/nfsclient/nfs_subs.c

Modified: head/sys/nfsclient/nfs_subs.c
==============================================================================
--- head/sys/nfsclient/nfs_subs.c	Fri Aug 14 10:57:57 2009	(r196204)
+++ head/sys/nfsclient/nfs_subs.c	Fri Aug 14 10:59:17 2009	(r196205)
@@ -409,28 +409,25 @@ int
 nfs_upgrade_vnlock(struct vnode *vp)
 {
 	int old_lock;
-	
- 	if ((old_lock = VOP_ISLOCKED(vp)) != LK_EXCLUSIVE) {
- 		if (old_lock == LK_SHARED) {
- 			/* Upgrade to exclusive lock, this might block */
- 			vn_lock(vp, LK_UPGRADE | LK_RETRY);
- 		} else {
- 			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
- 		}
+
+	ASSERT_VOP_LOCKED(vp, "nfs_upgrade_vnlock");
+	old_lock = VOP_ISLOCKED(vp);
+	if (old_lock != LK_EXCLUSIVE) {
+		KASSERT(old_lock == LK_SHARED,
+		    ("nfs_upgrade_vnlock: wrong old_lock %d", old_lock));
+		/* Upgrade to exclusive lock, this might block */
+		vn_lock(vp, LK_UPGRADE | LK_RETRY);
   	}
-	return old_lock;
+	return (old_lock);
 }
 
 void
 nfs_downgrade_vnlock(struct vnode *vp, int old_lock)
 {
 	if (old_lock != LK_EXCLUSIVE) {
- 		if (old_lock == LK_SHARED) {
- 			/* Downgrade from exclusive lock, this might block */
- 			vn_lock(vp, LK_DOWNGRADE);
- 		} else {
- 			VOP_UNLOCK(vp, 0);
- 		}
+		KASSERT(old_lock == LK_SHARED, ("wrong old_lock %d", old_lock));
+		/* Downgrade from exclusive lock. */
+		vn_lock(vp, LK_DOWNGRADE | LK_RETRY);
   	}
 }