pNFS: Ensure we check layout segment validity in the pg_init() callback

If we have a layout segment cached in pgio->pg_lseg, we should check it
for validity before reusing it in a new RPC request. Otherwise, if we
recoalesce, we can end up looping forever.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/filelayout/filelayout.c

@@ -933,6 +933,7 @@ static void
 filelayout_pg_init_read(struct nfs_pageio_descriptor *pgio,
 			struct nfs_page *req)
 {
+	pnfs_generic_pg_check_layout(pgio);
 	if (!pgio->pg_lseg) {
 		pgio->pg_lseg = fl_pnfs_update_layout(pgio->pg_inode,
 						      req->wb_context,
@@ -959,6 +960,7 @@ filelayout_pg_init_write(struct nfs_pageio_descriptor *pgio,
 	struct nfs_commit_info cinfo;
 	int status;
 
+	pnfs_generic_pg_check_layout(pgio);
 	if (!pgio->pg_lseg) {
 		pgio->pg_lseg = fl_pnfs_update_layout(pgio->pg_inode,
 						      req->wb_context,

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -846,6 +846,7 @@ ff_layout_pg_init_read(struct nfs_pageio_descriptor *pgio,
 	int ds_idx;
 
 retry:
+	pnfs_generic_pg_check_layout(pgio);
 	/* Use full layout for now */
 	if (!pgio->pg_lseg)
 		ff_layout_pg_get_read(pgio, req, false);
@@ -894,6 +895,7 @@ ff_layout_pg_init_write(struct nfs_pageio_descriptor *pgio,
 	int status;
 
 retry:
+	pnfs_generic_pg_check_layout(pgio);
 	if (!pgio->pg_lseg) {
 		pgio->pg_lseg = pnfs_update_layout(pgio->pg_inode,
 						   req->wb_context,

fs/nfs/pnfs.c

@@ -2072,11 +2072,23 @@ void pnfs_error_mark_layout_for_return(struct inode *inode,
 }
 EXPORT_SYMBOL_GPL(pnfs_error_mark_layout_for_return);
 
+void
+pnfs_generic_pg_check_layout(struct nfs_pageio_descriptor *pgio)
+{
+	if (pgio->pg_lseg == NULL ||
+	    test_bit(NFS_LSEG_VALID, &pgio->pg_lseg->pls_flags))
+		return;
+	pnfs_put_lseg(pgio->pg_lseg);
+	pgio->pg_lseg = NULL;
+}
+EXPORT_SYMBOL_GPL(pnfs_generic_pg_check_layout);
+
 void
 pnfs_generic_pg_init_read(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
 {
 	u64 rd_size = req->wb_bytes;
 
+	pnfs_generic_pg_check_layout(pgio);
 	if (pgio->pg_lseg == NULL) {
 		if (pgio->pg_dreq == NULL)
 			rd_size = i_size_read(pgio->pg_inode) - req_offset(req);
@@ -2107,6 +2119,7 @@ void
 pnfs_generic_pg_init_write(struct nfs_pageio_descriptor *pgio,
 			   struct nfs_page *req, u64 wb_size)
 {
+	pnfs_generic_pg_check_layout(pgio);
 	if (pgio->pg_lseg == NULL) {
 		pgio->pg_lseg = pnfs_update_layout(pgio->pg_inode,
 						   req->wb_context,

fs/nfs/pnfs.h

@@ -234,6 +234,7 @@ void pnfs_put_lseg_locked(struct pnfs_layout_segment *lseg);
 
 void set_pnfs_layoutdriver(struct nfs_server *, const struct nfs_fh *, struct nfs_fsinfo *);
 void unset_pnfs_layoutdriver(struct nfs_server *);
+void pnfs_generic_pg_check_layout(struct nfs_pageio_descriptor *pgio);
 void pnfs_generic_pg_init_read(struct nfs_pageio_descriptor *, struct nfs_page *);
 int pnfs_generic_pg_readpages(struct nfs_pageio_descriptor *desc);
 void pnfs_generic_pg_init_write(struct nfs_pageio_descriptor *pgio,