commit 5a6c59a6a8ccb63ae1b124fb6b5b611b19528ea9
Author: Mateusz Guzik <mjguzik@gmail.com>
Date:   Tue Oct 27 17:17:13 2020 -0400

    vfs: NDREINIT

diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
index 85f54e0ecfc9..6b110f78925d 100644
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -508,11 +508,15 @@ namei(struct nameidata *ndp)
 	 * While NDINIT may seem like a more natural place to do it, there are
 	 * callers which directly modify flags past invoking init.
 	 */
-	cnp->cn_origflags = cnp->cn_flags;
+	KASSERT(cnp->cn_flags != 0, ("%s: passed in cn_flags are 0\n", __func__));
+	KASSERT(cnp->cn_debugflags == 0,
+	    ("%s: ndp already has debugflags != 0 (%" PRIx64 "), missed NDREINIT?\n",
+	    __func__, cnp->cn_debugflags));
+	cnp->cn_debugflags = cnp->cn_flags;
+	if (ndp->ni_startdir != NULL)
+		cnp->cn_debugflags |= DBG_HADSTARTDIR;
 #endif
 	ndp->ni_cnd.cn_cred = ndp->ni_cnd.cn_thread->td_ucred;
-	KASSERT(ndp->ni_resflags == 0, ("%s: garbage in ni_resflags: %x\n",
-	    __func__, ndp->ni_resflags));
 	KASSERT(cnp->cn_cred && td->td_proc, ("namei: bad cred/proc"));
 	KASSERT((cnp->cn_flags & NAMEI_INTERNAL_FLAGS) == 0,
 	    ("namei: unexpected flags: %" PRIx64 "\n",
@@ -523,6 +527,7 @@ namei(struct nameidata *ndp)
 	MPASS(ndp->ni_startdir == NULL || ndp->ni_startdir->v_type == VDIR ||
 	    ndp->ni_startdir->v_type == VBAD);
 
+	ndp->ni_resflags = 0;
 	ndp->ni_lcf = 0;
 	ndp->ni_vp = NULL;
 
@@ -1509,7 +1514,7 @@ NDVALIDATE(struct nameidata *ndp)
 	u_int64_t used, orig;
 
 	cnp = &ndp->ni_cnd;
-	orig = cnp->cn_origflags;
+	orig = cnp->cn_debugflags & ~(DBG_HADSTARTDIR);
 	used = cnp->cn_flags;
 	switch (cnp->cn_nameiop) {
 	case LOOKUP:
@@ -1546,7 +1551,7 @@ NDVALIDATE(struct nameidata *ndp)
 	panic("%s: mismatched flags for op %d: added %" PRIx64 ", "
 	    "removed %" PRIx64" (%" PRIx64" != %" PRIx64"; stored %" PRIx64" != %" PRIx64")",
 	    __func__, cnp->cn_nameiop, used & ~orig, orig &~ used,
-	    orig, used, cnp->cn_origflags, cnp->cn_flags);
+	    orig, used, cnp->cn_debugflags, cnp->cn_flags);
 }
 #endif
 
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index 5c07afcc02e7..34d00d23806c 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -256,6 +256,7 @@ vn_open_cred(struct nameidata *ndp, int *flagp, int cmode, u_int vn_open_flags,
 			if (vn_start_write(ndp->ni_dvp, &mp, V_NOWAIT) != 0) {
 				NDFREE(ndp, NDF_ONLY_PNBUF);
 				vput(ndp->ni_dvp);
+				NDREINIT(ndp);
 				if ((error = vn_start_write(NULL, &mp,
 				    V_XSLEEP | PCATCH)) != 0)
 					return (error);
diff --git a/sys/sys/namei.h b/sys/sys/namei.h
index 09b95510443a..59bc5c1b58cd 100644
--- a/sys/sys/namei.h
+++ b/sys/sys/namei.h
@@ -46,7 +46,7 @@ struct componentname {
 	/*
 	 * Arguments to lookup.
 	 */
-	u_int64_t cn_origflags;	/* flags to namei */
+	u_int64_t cn_debugflags;/* debug flags used by namei */
 	u_int64_t cn_flags;	/* flags to namei */
 	struct	thread *cn_thread;/* thread requesting lookup */
 	struct	ucred *cn_cred;	/* credentials */
@@ -166,7 +166,7 @@ int	cache_fplookup(struct nameidata *ndp, enum cache_fpl_status *status,
 #define	NOCAPCHECK	0x00100000 /* do not perform capability checks */
 /* UNUSED		0x00200000 */
 /* UNUSED		0x00400000 */
-/* UNUSED		0x00800000 */
+#define	DBG_HADSTARTDIR	0x00800000 /* DEBUG: caller passed ni_startdir != NULL */
 #define	HASBUF		0x01000000 /* has allocated pathname buffer */
 #define	NOEXECCHECK	0x02000000 /* do not perform exec check on dir */
 #define	MAKEENTRY	0x04000000 /* entry is to be added to name cache */
@@ -180,8 +180,8 @@ int	cache_fplookup(struct nameidata *ndp, enum cache_fpl_status *status,
  * Flags which must not be passed in by callers.
  */
 #define NAMEI_INTERNAL_FLAGS	\
-	(HASBUF | NOEXECCHECK | MAKEENTRY | ISSYMLINK | ISLASTCN | ISDOTDOT | \
-	 TRAILINGSLASH)
+	(DBG_HADSTARTDIR | HASBUF | NOEXECCHECK | MAKEENTRY | ISSYMLINK | \
+	 ISLASTCN | ISDOTDOT | TRAILINGSLASH)
 
 /*
  * Namei results flags
@@ -215,8 +215,16 @@ int	cache_fplookup(struct nameidata *ndp, enum cache_fpl_status *status,
  */
 #ifdef INVARIANTS
 #define NDINIT_PREFILL(arg)	memset(arg, 0xff, sizeof(*arg))
+#define NDINIT_DEBUG(arg)	{ (arg)->ni_cnd.cn_debugflags = 0; }
+#define NDREINIT_DEBUG(arg) {						\
+	if ((arg)->ni_cnd.cn_debugflags & DBG_HADSTARTDIR)			\
+		panic("NDREINIT on ndp with DBG_HADSTARTDIR");			\
+	(arg)->ni_cnd.cn_debugflags = 0;					\
+}
 #else
 #define NDINIT_PREFILL(arg)	do { } while (0)
+#define NDINIT_DEBUG(arg)	do { } while (0)
+#define NDREINIT_DEBUG(arg)	do { } while (0)
 #endif
 
 #define NDINIT_ALL(ndp, op, flags, segflg, namep, dirfd, startdir, rightsp, td)	\
@@ -225,18 +233,25 @@ do {										\
 	cap_rights_t *_rightsp = (rightsp);					\
 	MPASS(_rightsp != NULL);						\
 	NDINIT_PREFILL(_ndp);							\
+	NDINIT_DEBUG(_ndp);							\
 	_ndp->ni_cnd.cn_nameiop = op;						\
 	_ndp->ni_cnd.cn_flags = flags;						\
 	_ndp->ni_segflg = segflg;						\
 	_ndp->ni_dirp = namep;							\
 	_ndp->ni_dirfd = dirfd;							\
 	_ndp->ni_startdir = startdir;						\
-	_ndp->ni_resflags = 0;							\
 	filecaps_init(&_ndp->ni_filecaps);					\
 	_ndp->ni_cnd.cn_thread = td;						\
 	_ndp->ni_rightsneeded = _rightsp;					\
 } while (0)
 
+#define NDREINIT(ndp)								\
+do {										\
+	struct nameidata *_ndp = (ndp);						\
+	NDREINIT_DEBUG(_ndp);							\
+	_ndp->ni_startdir = NULL;						\
+} while (0)
+
 #define NDF_NO_DVP_RELE		0x00000001
 #define NDF_NO_DVP_UNLOCK	0x00000002
 #define NDF_NO_DVP_PUT		0x00000003