NFSv4.1: nfs4_fl_prepare_ds must be careful about reporting success.

Various places assume that if nfs4_fl_prepare_ds() turns a non-NULL 'ds',
then ds->ds_clp will also be non-NULL.

This is not necessasrily true in the case when the process received a fatal signal
while nfs4_pnfs_ds_connect is waiting in nfs4_wait_ds_connect().
In that case ->ds_clp may not be set, and the devid may not recently have been marked
unavailable.

So add a test for ds_clp == NULL and return NULL in that case.

Fixes: c23266d ("NFS4.1 Fix data server connection race")
Signed-off-by: NeilBrown <[email protected]>
Acked-by: Olga Kornievskaia <[email protected]>
Acked-by: Adamson, Andy <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>

Author: NeilBrown

fs/nfs/filelayout/filelayoutdev.c

@@ -282,7 +282,8 @@ nfs4_fl_prepare_ds(struct pnfs_layout_segment *lseg, u32 ds_idx)
 			     s->nfs_client->cl_minorversion);
 
 out_test_devid:
-	if (filelayout_test_devid_unavailable(devid))
+	if (ret->ds_clp == NULL ||
+	    filelayout_test_devid_unavailable(devid))
 		ret = NULL;
 out:
 	return ret;