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>

1 files changed, 12 insertions, 3 deletions

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) {