Close a race in NFS lookup processing that could result in stale name cache

entries on one client when a directory was renamed on another client.  The
root cause for the stale entry being trusted is that each per-vnode nfsnode
structure has a single 'n_ctime' timestamp used to validate positive name
cache entries.  However, if there are multiple entries for a single vnode,
they all share a single timestamp.  To fix this, extend the name cache
to allow filesystems to optionally store a timestamp value in each name
cache entry.  The NFS clients now fetch the timestamp associated with
each name cache entry and use that to validate cache hits instead of the
timestamps previously stored in the nfsnode.  Another part of the fix is
that the NFS clients now use timestamps from the post-op attributes of
RPCs when adding name cache entries rather than pulling the timestamps out
of the file's attribute cache.  The latter is subject to races with other
lookups updating the attribute cache concurrently.  Some more details:
- Add a variant of nfsm_postop_attr() to the old NFS client that can return
  a vattr structure with a copy of the post-op attributes.
- Handle lookups of "." as a special case in the NFS clients since the name
  cache does not store name cache entries for ".", so we cannot get a
  useful timestamp.  It didn't really make much sense to recheck the
  attributes on the the directory to validate the namecache hit for "."
  anyway.
- ABI compat shims for the name cache routines are present in this commit
  so that it is safe to MFC.

MFC after:	2 weeks

1 files changed, 4 insertions, 4 deletions

diff --git a/sys/nfsclient/nfs_subs.c b/sys/nfsclient/nfs_subs.c
index 19fde06..d00a025 100644
--- a/sys/nfsclient/nfs_subs.c
+++ b/sys/nfsclient/nfs_subs.c
@@ -978,8 +978,8 @@ nfsm_loadattr_xx(struct vnode **v, struct vattr *va, struct mbuf **md,
 }
 
 int
-nfsm_postop_attr_xx(struct vnode **v, int *f, struct mbuf **md,
-		    caddr_t *dpos)
+nfsm_postop_attr_xx(struct vnode **v, int *f, struct vattr *va,
+		    struct mbuf **md, caddr_t *dpos)
 {
 	u_int32_t *tl;
 	int t1;
@@ -990,7 +990,7 @@ nfsm_postop_attr_xx(struct vnode **v, int *f, struct mbuf **md,
 		return EBADRPC;
 	*f = fxdr_unsigned(int, *tl);
 	if (*f != 0) {
-		t1 = nfs_loadattrcache(&ttvp, md, dpos, NULL, 1);
+		t1 = nfs_loadattrcache(&ttvp, md, dpos, va, 1);
 		if (t1 != 0) {
 			*f = 0;
 			return t1;
@@ -1020,7 +1020,7 @@ nfsm_wcc_data_xx(struct vnode **v, int *f, struct mbuf **md, caddr_t *dpos)
 				  VTONFS(*v)->n_mtime.tv_nsec == fxdr_unsigned(u_int32_t, *(tl + 3))); 
 		mtx_unlock(&(VTONFS(*v))->n_mtx);
 	}
-	t1 = nfsm_postop_attr_xx(v, &ttattrf, md, dpos);
+	t1 = nfsm_postop_attr_xx(v, &ttattrf, NULL, md, dpos);
 	if (t1)
 		return t1;
 	if (*f)