NFSv4.2: Serialise O_DIRECT i/o and fallocate()

Ensure that all O_DIRECT reads and writes complete before calling
fallocate so that we don't race w.r.t. attribute updates.

Fixes: 99f2378 ("NFSv4.2: Always flush out writes in nfs42_proc_fallocate()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: Trond Myklebust

fs/nfs/nfs42proc.c

@@ -114,6 +114,7 @@ static int nfs42_proc_fallocate(struct rpc_message *msg, struct file *filep,
 	exception.inode = inode;
 	exception.state = lock->open_context->state;
 
+	nfs_file_block_o_direct(NFS_I(inode));
 	err = nfs_sync_inode(inode);
 	if (err)
 		goto out;