Problem to avoid processes getting stuck in "vmopar". From Ian's

mail:

	The problem seems to originate with NFS's postop_attr
	information that is returned with a read or write RPC.
	Within a vm_fault context, the code cannot deal with
	vnode_pager_setsize() shrinking a vnode.

	The workaround in the patch below stops the nfsm_postop_attr()
	macro from ever shrinking a vnode. If the new size in the
	postop_attr information is smaller, then it just sets the
	nfsnode n_attrstamp to 0 to stop the wrong size getting
	used in the future. This change only affects postop_attr
	attributes; the nfsm_loadattr() macro works as normal.

	The change is implemented by adding a new argument to
	nfs_loadattrcache() called 'dontshrink'. When this is
	non-zero, nfs_loadattrcache() will never reduce the
	vnode/nfsnode size; instead it zeros n_attrstamp.

There remain other was processes can get stuck in vmopar.

Submitted by:	Ian Dowse <iedowse@maths.tcd.ie>
Reviewed by:	dillon
Tested by:	Vadim Belman <voland@lflat.org>

4 files changed, 16 insertions, 7 deletions

diff --git a/sys/nfsserver/nfs.h b/sys/nfsserver/nfs.h
index e07a4f5..5c5a823 100644
--- a/sys/nfsserver/nfs.h
+++ b/sys/nfsserver/nfs.h
@@ -616,7 +616,7 @@ int	nfs_request __P((struct vnode *, struct mbuf *, int, struct proc *,
 			 struct ucred *, struct mbuf **, struct mbuf **,
 			 caddr_t *));
 int	nfs_loadattrcache __P((struct vnode **, struct mbuf **, caddr_t *,
-			       struct vattr *));
+			       struct vattr *, int));
 int	nfs_namei __P((struct nameidata *, fhandle_t *, int,
 		       struct nfssvc_sock *, struct sockaddr *, struct mbuf **,
 		       caddr_t *, struct vnode **, struct proc *, int, int));
diff --git a/sys/nfsserver/nfs_srvsubs.c b/sys/nfsserver/nfs_srvsubs.c
index 5934465..95f7d5b 100644
--- a/sys/nfsserver/nfs_srvsubs.c
+++ b/sys/nfsserver/nfs_srvsubs.c
@@ -1203,11 +1203,12 @@ nfs_uninit(vfsp)
  *    copy the attributes to *vaper
  */
 int
-nfs_loadattrcache(vpp, mdp, dposp, vaper)
+nfs_loadattrcache(vpp, mdp, dposp, vaper, dontshrink)
 	struct vnode **vpp;
 	struct mbuf **mdp;
 	caddr_t *dposp;
 	struct vattr *vaper;
+	int dontshrink;
 {
 	register struct vnode *vp = *vpp;
 	register struct vattr *vap;
@@ -1323,9 +1324,18 @@ nfs_loadattrcache(vpp, mdp, dposp, vaper)
 		vap->va_gen = fxdr_unsigned(u_int32_t,fp->fa2_ctime.nfsv2_usec);
 		vap->va_filerev = 0;
 	}
+	np->n_attrstamp = time_second;
 	if (vap->va_size != np->n_size) {
 		if (vap->va_type == VREG) {
-			if (np->n_flag & NMODIFIED) {
+			if (dontshrink && vap->va_size < np->n_size) {
+				/*
+				 * We've been told not to shrink the file;
+				 * zero np->n_attrstamp to indicate that
+				 * the attributes are stale.
+				 */
+				vap->va_size = np->n_size;
+				np->n_attrstamp = 0;
+			} else if (np->n_flag & NMODIFIED) {
 				if (vap->va_size < np->n_size)
 					vap->va_size = np->n_size;
 				else
@@ -1338,7 +1348,6 @@ nfs_loadattrcache(vpp, mdp, dposp, vaper)
 			np->n_size = vap->va_size;
 		}
 	}
-	np->n_attrstamp = time_second;
 	if (vaper != NULL) {
 		bcopy((caddr_t)vap, (caddr_t)vaper, sizeof(*vap));
 		if (np->n_flag & NCHG) {
diff --git a/sys/nfsserver/nfsm_subs.h b/sys/nfsserver/nfsm_subs.h
index b13c009..0990fe4 100644
--- a/sys/nfsserver/nfsm_subs.h
+++ b/sys/nfsserver/nfsm_subs.h
@@ -212,7 +212,7 @@ struct mbuf *nfsm_rpchead __P((struct ucred *cr, int nmflag, int procid,
 #define	nfsm_loadattr(v, a) \
 	do { \
 		struct vnode *ttvp = (v); \
-		if ((t1 = nfs_loadattrcache(&ttvp, &md, &dpos, (a))) != 0) { \
+		if ((t1 = nfs_loadattrcache(&ttvp, &md, &dpos, (a), 0)) != 0) { \
 			error = t1; \
 			m_freem(mrep); \
 			goto nfsmout; \
@@ -226,7 +226,7 @@ struct mbuf *nfsm_rpchead __P((struct ucred *cr, int nmflag, int procid,
 		nfsm_dissect(tl, u_int32_t *, NFSX_UNSIGNED); \
 		if (((f) = fxdr_unsigned(int, *tl)) != 0) { \
 			if ((t1 = nfs_loadattrcache(&ttvp, &md, &dpos, \
-				(struct vattr *)0)) != 0) { \
+				(struct vattr *)0, 1)) != 0) { \
 				error = t1; \
 				(f) = 0; \
 				m_freem(mrep); \
diff --git a/sys/nfsserver/nfsrvstats.h b/sys/nfsserver/nfsrvstats.h
index e07a4f5..5c5a823 100644
--- a/sys/nfsserver/nfsrvstats.h
+++ b/sys/nfsserver/nfsrvstats.h
@@ -616,7 +616,7 @@ int	nfs_request __P((struct vnode *, struct mbuf *, int, struct proc *,
 			 struct ucred *, struct mbuf **, struct mbuf **,
 			 caddr_t *));
 int	nfs_loadattrcache __P((struct vnode **, struct mbuf **, caddr_t *,
-			       struct vattr *));
+			       struct vattr *, int));
 int	nfs_namei __P((struct nameidata *, fhandle_t *, int,
 		       struct nfssvc_sock *, struct sockaddr *, struct mbuf **,
 		       caddr_t *, struct vnode **, struct proc *, int, int));