nfsd: only call inode_query_iversion in the I_VERSION case

inode_query_iversion() can modify i_version.  Depending on the exported
filesystem, that may not be safe.  For example, if you're re-exporting
NFS, NFS stores the server's change attribute in i_version and does not
expect it to be modified locally.  This has been observed causing
unnecessary cache invalidations.

The way a filesystem indicates that it's OK to call
inode_query_iverson() is by setting SB_I_VERSION.

So, move the I_VERSION check out of encode_change(), where it's used
only in GETATTR responses, to nfsd4_change_attribute(), which is
also called for pre- and post- operation attributes.

(Note we could also pull the NFSEXP_V4ROOT case into
nfsd4_change_attribute() as well.  That would actually be a no-op,
since pre/post attrs are only used for metadata-modifying operations,
and V4ROOT exports are read-only.  But we might make the change in
the future just for simplicity.)

Reported-by: Daire Byrne <daire@dneg.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs3xdr.c

@@ -291,14 +291,13 @@ void fill_post_wcc(struct svc_fh *fhp)
 		printk("nfsd: inode locked twice during operation.\n");
 
 	err = fh_getattr(fhp, &fhp->fh_post_attr);
-	fhp->fh_post_change = nfsd4_change_attribute(&fhp->fh_post_attr,
-						     d_inode(fhp->fh_dentry));
 	if (err) {
 		fhp->fh_post_saved = false;
-		/* Grab the ctime anyway - set_change_info might use it */
 		fhp->fh_post_attr.ctime = d_inode(fhp->fh_dentry)->i_ctime;
 	} else
 		fhp->fh_post_saved = true;
+	fhp->fh_post_change = nfsd4_change_attribute(&fhp->fh_post_attr,
+						     d_inode(fhp->fh_dentry));
 }
 
 /*

fs/nfsd/nfs4xdr.c

@@ -2426,12 +2426,8 @@ static __be32 *encode_change(__be32 *p, struct kstat *stat, struct inode *inode,
 	if (exp->ex_flags & NFSEXP_V4ROOT) {
 		*p++ = cpu_to_be32(convert_to_wallclock(exp->cd->flush_time));
 		*p++ = 0;
-	} else if (IS_I_VERSION(inode)) {
+	} else
 		p = xdr_encode_hyper(p, nfsd4_change_attribute(stat, inode));
-	} else {
-		*p++ = cpu_to_be32(stat->ctime.tv_sec);
-		*p++ = cpu_to_be32(stat->ctime.tv_nsec);
-	}
 	return p;
 }
 

fs/nfsd/nfsfh.h

@@ -261,10 +261,16 @@ static inline u64 nfsd4_change_attribute(struct kstat *stat,
 {
 	u64 chattr;
 
-	chattr =  stat->ctime.tv_sec;
-	chattr <<= 30;
-	chattr += stat->ctime.tv_nsec;
-	chattr += inode_query_iversion(inode);
+	if (IS_I_VERSION(inode)) {
+		chattr =  stat->ctime.tv_sec;
+		chattr <<= 30;
+		chattr += stat->ctime.tv_nsec;
+		chattr += inode_query_iversion(inode);
+	} else {
+		chattr = stat->ctime.tv_sec;
+		chattr <<= 32;
+		chattr += stat->ctime.tv_nsec;
+	}
 	return chattr;
 }