From 19feaba08bc6b84c117bd21cc71e139c6d086ed7 Mon Sep 17 00:00:00 2001
From: jhb <jhb@FreeBSD.org>
Date: Thu, 8 Mar 2012 20:27:20 +0000
Subject: Add KTR_VFS traces to track modifications to a vnode's writecount.

---
 sys/fs/unionfs/union_subr.c |  4 ++++
 sys/kern/vfs_syscalls.c     | 10 ++++++++--
 sys/kern/vfs_vnops.c        |  7 ++++++-
 sys/ufs/ufs/ufs_extattr.c   |  2 ++
 sys/vm/vnode_pager.c        |  6 ++++++
 5 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/sys/fs/unionfs/union_subr.c b/sys/fs/unionfs/union_subr.c
index 2e74844..074958c 100644
--- a/sys/fs/unionfs/union_subr.c
+++ b/sys/fs/unionfs/union_subr.c
@@ -952,6 +952,8 @@ unionfs_vn_create_on_upper(struct vnode **vpp, struct vnode *udvp,
 		goto unionfs_vn_create_on_upper_free_out1;
 	}
 	vp->v_writecount++;
+	CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",  __func__, vp,
+	    vp->v_writecount);
 	*vpp = vp;
 
 unionfs_vn_create_on_upper_free_out1:
@@ -1087,6 +1089,8 @@ unionfs_copyfile(struct unionfs_node *unp, int docopy, struct ucred *cred,
 	}
 	VOP_CLOSE(uvp, FWRITE, cred, td);
 	uvp->v_writecount--;
+	CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d", __func__, uvp,
+	    uvp->v_writecount);
 
 	vn_finished_write(mp);
 
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 9b7cbe4..a8bb661 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -4591,16 +4591,22 @@ sys_fhopen(td, uap)
 	if (error)
 		goto bad;
 
-	if (fmode & FWRITE)
+	if (fmode & FWRITE) {
 		vp->v_writecount++;
+		CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",
+		    __func__, vp, vp->v_writecount);
+	}
 
 	/*
 	 * end of vn_open code
 	 */
 
 	if ((error = falloc(td, &nfp, &indx, fmode)) != 0) {
-		if (fmode & FWRITE)
+		if (fmode & FWRITE) {
 			vp->v_writecount--;
+			CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
+			    __func__, vp, vp->v_writecount);
+		}
 		goto bad;
 	}
 	/* An extra reference on `nfp' has been held for us by falloc(). */
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index ce2d701..d4b60f1 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -245,8 +245,11 @@ restart:
 	if ((error = VOP_OPEN(vp, fmode, cred, td, fp)) != 0)
 		goto bad;
 
-	if (fmode & FWRITE)
+	if (fmode & FWRITE) {
 		vp->v_writecount++;
+		CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",
+		    __func__, vp, vp->v_writecount);
+	}
 	*flagp = fmode;
 	ASSERT_VOP_LOCKED(vp, "vn_open_cred");
 	if (!mpsafe)
@@ -309,6 +312,8 @@ vn_close(vp, flags, file_cred, td)
 		VNASSERT(vp->v_writecount > 0, vp, 
 		    ("vn_close: negative writecount"));
 		vp->v_writecount--;
+		CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
+		    __func__, vp, vp->v_writecount);
 	}
 	error = VOP_CLOSE(vp, flags, file_cred, td);
 	vput(vp);
diff --git a/sys/ufs/ufs/ufs_extattr.c b/sys/ufs/ufs/ufs_extattr.c
index 777f385..210d05a 100644
--- a/sys/ufs/ufs/ufs_extattr.c
+++ b/sys/ufs/ufs/ufs_extattr.c
@@ -335,6 +335,8 @@ ufs_extattr_enable_with_open(struct ufsmount *ump, struct vnode *vp,
 	}
 
 	vp->v_writecount++;
+	CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d", __func__, vp,
+	    vp->v_writecount);
 
 	vref(vp);
 
diff --git a/sys/vm/vnode_pager.c b/sys/vm/vnode_pager.c
index 609205a..c5b6c17 100644
--- a/sys/vm/vnode_pager.c
+++ b/sys/vm/vnode_pager.c
@@ -272,6 +272,8 @@ vnode_pager_dealloc(object)
 	if (object->un_pager.vnp.writemappings > 0) {
 		object->un_pager.vnp.writemappings = 0;
 		vp->v_writecount--;
+		CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
+		    __func__, vp, vp->v_writecount);
 	}
 	vp->v_object = NULL;
 	vp->v_vflag &= ~VV_TEXT;
@@ -1241,9 +1243,13 @@ vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
 	if (old_wm == 0 && object->un_pager.vnp.writemappings != 0) {
 		ASSERT_VOP_ELOCKED(vp, "v_writecount inc");
 		vp->v_writecount++;
+		CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",
+		    __func__, vp, vp->v_writecount);
 	} else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
 		ASSERT_VOP_ELOCKED(vp, "v_writecount dec");
 		vp->v_writecount--;
+		CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
+		    __func__, vp, vp->v_writecount);
 	}
 	VM_OBJECT_UNLOCK(object);
 }
-- 
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