NFS: Zero-stateid SETATTR should first return delegation

If a write delegation isn't available, the Linux NFS client uses
a zero-stateid when performing a SETATTR.

NFSv4.0 provides no mechanism for an NFS server to match such a
request to a particular client. It recalls all delegations for that
file, even delegations held by the client issuing the request. If
that client happens to hold a read delegation, the server will
recall it immediately, resulting in an NFS4ERR_DELAY/CB_RECALL/
DELEGRETURN sequence.

Optimize out this pipeline bubble by having the client return any
delegations it may hold on a file before it issues a
SETATTR(zero-stateid) on that file.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 4a6cfb497103a3de116b6efd7c3aff613612b7b7..3e824110b47038b733e043f8ad5616eddc4d11ca 100644 (file)
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3293,8 +3293,10 @@ static int _nfs4_do_setattr(struct inode *inode,
 
        /* Servers should only apply open mode checks for file size changes */
        truncate = (arg->iap->ia_valid & ATTR_SIZE) ? true : false;
-       if (!truncate)
+       if (!truncate) {
+               nfs4_inode_make_writeable(inode);
                goto zero_stateid;
+       }
 
        if (nfs4_copy_delegation_stateid(inode, FMODE_WRITE, &arg->stateid, &delegation_cred)) {
                /* Use that stateid */