nfs: Fetch MOUNTED_ON_FILEID when updating an inode

2ef47eb1 (NFS: Fix use of nfs_attr_use_mounted_on_fileid()) was a good
start to fixing a circular directory structure warning for NFS v4
"junctioned" mountpoints.  Unfortunately, further testing continued to
generate this error.

My server is configured like this:

anna@nfsd ~ % df
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1       9.1G  2.0G  6.5G  24% /
/dev/vdc1      1014M   33M  982M   4% /exports
/dev/vdc2      1014M   33M  982M   4% /exports/vol1
/dev/vdc3      1014M   33M  982M   4% /exports/vol1/vol2

anna@nfsd ~ % cat /etc/exports
/exports/          *(rw,async,no_subtree_check,no_root_squash)
/exports/vol1/     *(rw,async,no_subtree_check,no_root_squash)
/exports/vol1/vol2 *(rw,async,no_subtree_check,no_root_squash)

I've been running chown across the entire mountpoint twice in a row to
hit this problem.  The first run succeeds, but the second one fails with
the circular directory warning along with:

anna@client ~ % dmesg
[Apr 3 14:28] NFS: server 192.168.100.204 error: fileid changed
              fsid 0:39: expected fileid 0x100080, got 0x80

WHere 0x80 is the mountpoint's fileid and 0x100080 is the mounted-on
fileid.

This patch fixes the issue by requesting an updated mounted-on fileid
from the server during nfs_update_inode(), and then checking that the
fileid stored in the nfs_inode matches either the fileid or mounted-on
fileid returned by the server.
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/inode.c

@@ -1593,6 +1593,19 @@ int nfs_post_op_update_inode_force_wcc(struct inode *inode, struct nfs_fattr *fa
 }
 EXPORT_SYMBOL_GPL(nfs_post_op_update_inode_force_wcc);
 
+
+static inline bool nfs_fileid_valid(struct nfs_inode *nfsi,
+				    struct nfs_fattr *fattr)
+{
+	bool ret1 = true, ret2 = true;
+
+	if (fattr->valid & NFS_ATTR_FATTR_FILEID)
+		ret1 = (nfsi->fileid == fattr->fileid);
+	if (fattr->valid & NFS_ATTR_FATTR_MOUNTED_ON_FILEID)
+		ret2 = (nfsi->fileid == fattr->mounted_on_fileid);
+	return ret1 || ret2;
+}
+
 /*
  * Many nfs protocol calls return the new file attributes after
  * an operation.  Here we update the inode to reflect the state
@@ -1619,7 +1632,7 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
 			nfs_display_fhandle_hash(NFS_FH(inode)),
 			atomic_read(&inode->i_count), fattr->valid);
 
-	if ((fattr->valid & NFS_ATTR_FATTR_FILEID) && nfsi->fileid != fattr->fileid) {
+	if (!nfs_fileid_valid(nfsi, fattr)) {
 		printk(KERN_ERR "NFS: server %s error: fileid changed\n"
 			"fsid %s: expected fileid 0x%Lx, got 0x%Lx\n",
 			NFS_SERVER(inode)->nfs_client->cl_hostname,

fs/nfs/nfs4proc.c

@@ -185,7 +185,8 @@ const u32 nfs4_fattr_bitmap[3] = {
 	| FATTR4_WORD1_SPACE_USED
 	| FATTR4_WORD1_TIME_ACCESS
 	| FATTR4_WORD1_TIME_METADATA
-	| FATTR4_WORD1_TIME_MODIFY,
+	| FATTR4_WORD1_TIME_MODIFY
+	| FATTR4_WORD1_MOUNTED_ON_FILEID,
 #ifdef CONFIG_NFS_V4_SECURITY_LABEL
 	FATTR4_WORD2_SECURITY_LABEL
 #endif