Author: rmacklem
Date: Wed Oct 22 20:47:11 2014
New Revision: 273481
URL: https://svnweb.freebsd.org/changeset/base/273481

Log:
  Clip the settings for the NFS rsize, wsize mount options
  to a power of 2. For non-power of 2 settings, intermittent
  page faults have been reported. Although the bug that causes
  these page faults/crashes has not been identified, it does
  not appear to occur when rsize, wsize is a power of 2.
  
  Reported by:  tcber...@gmail.com
  MFC after:    2 weeks

Modified:
  head/sys/fs/nfsclient/nfs_clvfsops.c

Modified: head/sys/fs/nfsclient/nfs_clvfsops.c
==============================================================================
--- head/sys/fs/nfsclient/nfs_clvfsops.c        Wed Oct 22 18:55:44 2014        
(r273480)
+++ head/sys/fs/nfsclient/nfs_clvfsops.c        Wed Oct 22 20:47:11 2014        
(r273481)
@@ -552,7 +552,7 @@ static void
 nfs_decode_args(struct mount *mp, struct nfsmount *nmp, struct nfs_args *argp,
     const char *hostname, struct ucred *cred, struct thread *td)
 {
-       int s;
+       int i, s;
        int adjsock;
        char *p;
 
@@ -621,18 +621,36 @@ nfs_decode_args(struct mount *mp, struct
 
        if ((argp->flags & NFSMNT_WSIZE) && argp->wsize > 0) {
                nmp->nm_wsize = argp->wsize;
-               /* Round down to multiple of blocksize */
-               nmp->nm_wsize &= ~(NFS_FABLKSIZE - 1);
-               if (nmp->nm_wsize <= 0)
-                       nmp->nm_wsize = NFS_FABLKSIZE;
+               /*
+                * Clip at the power of 2 below the size. There is an
+                * issue (not isolated) that causes intermittent page
+                * faults if this is not done.
+                */
+               i = NFS_FABLKSIZE;
+               for (;;) {
+                       if (i * 2 > nmp->nm_wsize) {
+                               nmp->nm_wsize = i;
+                               break;
+                       }
+                       i *= 2;
+               }
        }
 
        if ((argp->flags & NFSMNT_RSIZE) && argp->rsize > 0) {
                nmp->nm_rsize = argp->rsize;
-               /* Round down to multiple of blocksize */
-               nmp->nm_rsize &= ~(NFS_FABLKSIZE - 1);
-               if (nmp->nm_rsize <= 0)
-                       nmp->nm_rsize = NFS_FABLKSIZE;
+               /*
+                * Clip at the power of 2 below the size. There is an
+                * issue (not isolated) that causes intermittent page
+                * faults if this is not done.
+                */
+               i = NFS_FABLKSIZE;
+               for (;;) {
+                       if (i * 2 > nmp->nm_rsize) {
+                               nmp->nm_rsize = i;
+                               break;
+                       }
+                       i *= 2;
+               }
        }
 
        if ((argp->flags & NFSMNT_READDIRSIZE) && argp->readdirsize > 0) {
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