NFS: Fix a wraparound issue with nfsi->cache_change_attribute

Fix wraparound issue with nfsi->cache_change_attribute. If it is found
to lie in the future, then update it to lie in the past. Patch based on
a suggestion by Neil Brown.

..and minor micro-optimisation: avoid reading 'jiffies' more than once in
nfs_update_inode().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 13 insertions, 8 deletions

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 4ef454763886..93269c3dd0f3 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -939,6 +939,7 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
         struct nfs_inode *nfsi = NFS_I(inode);
         loff_t cur_isize, new_isize;
         unsigned int    invalid = 0;
+        unsigned long now = jiffies;
         int data_stable;
 
         dfprintk(VFS, "NFS: %s(%s/%ld ct=%d info=0x%x)\n",
@@ -964,7 +965,11 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
          * Update the read time so we don't revalidate too often.
          */
         nfsi->read_cache_jiffies = fattr->time_start;
-        nfsi->last_updated = jiffies;
+        nfsi->last_updated = now;
+
+        /* Fix a wraparound issue with nfsi->cache_change_attribute */
+        if (time_before(now, nfsi->cache_change_attribute))
+                nfsi->cache_change_attribute = now - 600*HZ;
 
         /* Are we racing with known updates of the metadata on the server? */
         data_stable = nfs_verify_change_attribute(inode, fattr->time_start);
@@ -990,7 +995,7 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
                         inode->i_size = new_isize;
                         invalid |= NFS_INO_INVALID_ATTR|NFS_INO_INVALID_DATA;
                 }
-                nfsi->cache_change_attribute = jiffies;
+                nfsi->cache_change_attribute = now;
                 dprintk("NFS: isize change on server for file %s/%ld\n",
                                 inode->i_sb->s_id, inode->i_ino);
         }
@@ -1001,14 +1006,14 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
                 dprintk("NFS: mtime change on server for file %s/%ld\n",
                                 inode->i_sb->s_id, inode->i_ino);
                 invalid |= NFS_INO_INVALID_ATTR|NFS_INO_INVALID_DATA;
-                nfsi->cache_change_attribute = jiffies;
+                nfsi->cache_change_attribute = now;
         }
 
         /* If ctime has changed we should definitely clear access+acl caches */
         if (!timespec_equal(&inode->i_ctime, &fattr->ctime)) {
                 invalid |= NFS_INO_INVALID_ACCESS|NFS_INO_INVALID_ACL;
                 memcpy(&inode->i_ctime, &fattr->ctime, sizeof(inode->i_ctime));
-                nfsi->cache_change_attribute = jiffies;
+                nfsi->cache_change_attribute = now;
         }
         memcpy(&inode->i_atime, &fattr->atime, sizeof(inode->i_atime));
 
@@ -1037,18 +1042,18 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
                                 inode->i_sb->s_id, inode->i_ino);
                 nfsi->change_attr = fattr->change_attr;
                 invalid |= NFS_INO_INVALID_ATTR|NFS_INO_INVALID_DATA|NFS_INO_INVALID_ACCESS|NFS_INO_INVALID_ACL;
-                nfsi->cache_change_attribute = jiffies;
+                nfsi->cache_change_attribute = now;
         }
 
         /* Update attrtimeo value if we're out of the unstable period */
         if (invalid & NFS_INO_INVALID_ATTR) {
                 nfs_inc_stats(inode, NFSIOS_ATTRINVALIDATE);
                 nfsi->attrtimeo = NFS_MINATTRTIMEO(inode);
-                nfsi->attrtimeo_timestamp = jiffies;
-        } else if (time_after(jiffies, nfsi->attrtimeo_timestamp+nfsi->attrtimeo)) {
+                nfsi->attrtimeo_timestamp = now;
+        } else if (time_after(now, nfsi->attrtimeo_timestamp+nfsi->attrtimeo)) {
                 if ((nfsi->attrtimeo <<= 1) > NFS_MAXATTRTIMEO(inode))
                         nfsi->attrtimeo = NFS_MAXATTRTIMEO(inode);
-                nfsi->attrtimeo_timestamp = jiffies;
+                nfsi->attrtimeo_timestamp = now;
         }
         /* Don't invalidate the data if we were to blame */
         if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)