Index: src/sys/kern/vfs_bio.c
===================================================================
RCS file: /home/chs/netbsd/cvs/src/sys/kern/vfs_bio.c,v
retrieving revision 1.296
diff -u -p -r1.296 vfs_bio.c
--- src/sys/kern/vfs_bio.c	11 Jun 2020 19:20:46 -0000	1.296
+++ src/sys/kern/vfs_bio.c	30 Jul 2020 17:34:08 -0000
@@ -1516,6 +1516,36 @@ getnewbuf(int slpflag, int slptimeo, int
 }
 
 /*
+ * Invalidate the specified buffer if it exists.
+ */
+void
+binvalbuf(struct vnode *vp, daddr_t blkno)
+{
+	buf_t *bp;
+	int err;
+
+	mutex_enter(&bufcache_lock);
+
+ loop:
+	bp = incore(vp, blkno);
+	if (bp != NULL) {
+		err = bbusy(bp, 0, 0, NULL);
+		if (err == EPASSTHROUGH)
+			goto loop;
+		bremfree(bp);
+		if (ISSET(bp->b_oflags, BO_DELWRI)) {
+			SET(bp->b_cflags, BC_NOCACHE);
+			mutex_exit(&bufcache_lock);
+			bwrite(bp);
+		} else {
+			brelsel(bp, BC_INVAL);
+			mutex_exit(&bufcache_lock);
+		}
+	} else
+		mutex_exit(&bufcache_lock);
+}
+
+/*
  * Attempt to free an aged buffer off the queues.
  * Called with queue lock held.
  * Returns the amount of buffer memory freed.
Index: src/sys/sys/buf.h
===================================================================
RCS file: /home/chs/netbsd/cvs/src/sys/sys/buf.h,v
retrieving revision 1.133
diff -u -p -r1.133 buf.h
--- src/sys/sys/buf.h	20 Apr 2020 21:39:05 -0000	1.133
+++ src/sys/sys/buf.h	30 Jul 2020 16:01:48 -0000
@@ -287,6 +287,7 @@ buf_t	*incore(struct vnode *, daddr_t);
 int	allocbuf(buf_t *, int, int);
 void	brelsel(buf_t *, int);
 void	brelse(buf_t *, int);
+void	binvalbuf(struct vnode *, daddr_t);
 
 /*
  * So-far indeterminate ops that might belong to either
Index: src/sys/ufs/ffs/ffs_inode.c
===================================================================
RCS file: /home/chs/netbsd/cvs/src/sys/ufs/ffs/ffs_inode.c,v
retrieving revision 1.130
diff -u -p -r1.130 ffs_inode.c
--- src/sys/ufs/ffs/ffs_inode.c	26 Jul 2020 00:21:24 -0000	1.130
+++ src/sys/ufs/ffs/ffs_inode.c	30 Jul 2020 17:33:26 -0000
@@ -208,6 +208,7 @@ ffs_truncate(struct vnode *ovp, off_t le
 {
 	daddr_t lastblock;
 	struct inode *oip = VTOI(ovp);
+	struct mount *omp = ovp->v_mount;
 	daddr_t bn, lastiblock[UFS_NIADDR], indir_lbn[UFS_NIADDR];
 	daddr_t blks[UFS_NDADDR + UFS_NIADDR], oldblks[UFS_NDADDR + UFS_NIADDR];
 	struct fs *fs;
@@ -220,6 +221,8 @@ ffs_truncate(struct vnode *ovp, off_t le
 	int sync;
 	struct ufsmount *ump = oip->i_ump;
 	void *dcookie;
+	long bsize;
+	bool wapbl = omp->mnt_wapbl != NULL;
 
 	UFS_WAPBL_JLOCK_ASSERT(ump->um_mountp);
 
@@ -255,11 +258,11 @@ ffs_truncate(struct vnode *ovp, off_t le
 #ifdef QUOTA
 			(void) chkdq(oip, -extblocks, NOCRED, FORCE);
 #endif
-			vinvalbuf(ovp, 0, cred, curlwp, 0, 0);
 			osize = oip->i_din2->di_extsize;
 			oip->i_din2->di_blocks -= extblocks;
 			oip->i_din2->di_extsize = 0;
 			for (i = 0; i < UFS_NXADDR; i++) {
+				binvalbuf(ovp, -1 - i);
 				oldblks[i] = oip->i_din2->di_extb[i];
 				oip->i_din2->di_extb[i] = 0;
 			}
@@ -269,8 +272,15 @@ ffs_truncate(struct vnode *ovp, off_t le
 			for (i = 0; i < UFS_NXADDR; i++) {
 				if (oldblks[i] == 0)
 					continue;
-				ffs_blkfree(fs, oip->i_devvp, oldblks[i],
-				    ffs_sblksize(fs, osize, i), oip->i_number);
+				bsize = ffs_sblksize(fs, osize, i);
+				if (wapbl) {
+					error = UFS_WAPBL_REGISTER_DEALLOCATION(omp,
+					    FFS_FSBTODB(fs, oldblks[i]), bsize, NULL);
+					if (error)
+						return error;
+				} else 
+					ffs_blkfree(fs, oip->i_devvp, oldblks[i],
+					    bsize, oip->i_number);
 			}
 			extblocks = 0;
 		}
@@ -501,8 +511,6 @@ ffs_truncate(struct vnode *ovp, off_t le
 	 * All whole direct blocks or frags.
 	 */
 	for (i = UFS_NDADDR - 1; i > lastblock; i--) {
-		long bsize;
-
 		bn = ffs_getdb(fs, oip, i);
 		if (bn == 0)
 			continue;