pNFS: Fix a deadlock between read resends and layoutreturn

We must not call nfs_pageio_init_read() on a new nfs_pageio_descriptor
while holding a reference to a layout segment, as that can deadlock
pnfs_update_layout().

Fixes: d67ae825 ("pnfs/flexfiles: Add the FlexFile Layout Driver")
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Cc: stable@vger.kernel.org # v4.0+

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -28,6 +28,9 @@
 
 static struct group_info	*ff_zero_group;
 
+static void ff_layout_read_record_layoutstats_done(struct rpc_task *task,
+		struct nfs_pgio_header *hdr);
+
 static struct pnfs_layout_hdr *
 ff_layout_alloc_layout_hdr(struct inode *inode, gfp_t gfp_flags)
 {
@@ -1293,6 +1296,7 @@ static int ff_layout_read_done_cb(struct rpc_task *task,
 					hdr->pgio_mirror_idx + 1,
 					&hdr->pgio_mirror_idx))
 			goto out_eagain;
+		ff_layout_read_record_layoutstats_done(task, hdr);
 		pnfs_read_resend_pnfs(hdr);
 		return task->tk_status;
 	case -NFS4ERR_RESET_TO_MDS:

fs/nfs/pnfs.c

@@ -2286,6 +2286,10 @@ void pnfs_read_resend_pnfs(struct nfs_pgio_header *hdr)
 	struct nfs_pageio_descriptor pgio;
 
 	if (!test_and_set_bit(NFS_IOHDR_REDO, &hdr->flags)) {
+		/* Prevent deadlocks with layoutreturn! */
+		pnfs_put_lseg(hdr->lseg);
+		hdr->lseg = NULL;
+
 		nfs_pageio_init_read(&pgio, hdr->inode, false,
 					hdr->completion_ops);
 		hdr->task.tk_status = nfs_pageio_resend(&pgio, hdr);