NFSv2: Fix write regression

BugLink: https://bugs.launchpad.net/bugs/1845405

[ Upstream commit d33d4beb ]

Ensure we update the write result count on success, since the
RPC call itself does not do so.
Reported-by: Jan Stancek <jstancek@redhat.com>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/nfs/proc.c

@@ -610,8 +610,10 @@ static int nfs_proc_pgio_rpc_prepare(struct rpc_task *task,
 
 static int nfs_write_done(struct rpc_task *task, struct nfs_pgio_header *hdr)
 {
-	if (task->tk_status >= 0)
+	if (task->tk_status >= 0) {
+		hdr->res.count = hdr->args.count;
 		nfs_writeback_update_inode(hdr);
+	}
 	return 0;
 }