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: NTrond Myklebust <Trond.Myklebust@netapp.com>

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)