[PATCH 4.19 15/49] NFS: Zero-stateid SETATTR should first return delegation

From: Greg Kroah-Hartman
Date: Mon Sep 21 2020 - 12:42:31 EST

From: Chuck Lever <chuck.lever@xxxxxxxxxx>

[ Upstream commit 644c9f40cf71969f29add32f32349e71d4995c0b ]

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/

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@xxxxxxxxxx>
Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
fs/nfs/nfs4proc.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 929f1d72bfd39..b2a2ff3f22a46 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3129,8 +3129,10 @@ 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 */