NFSv4.1: Fix some issues with pnfs_generic_pg_test

1. If the intention is to coalesce requests 'prev' and 'req' then we
   have to ensure at least that we have a layout starting at
   req_offset(prev).

2. If we're only requesting a minimal layout of length desc->pg_count,
   we need to test the length actually returned by the server before
   we allow the coalescing to occur.

3. We need to deal correctly with (pgio->lseg == NULL)

4. Fixup the test guarding the pnfs_update_layout.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index 539b94cb6c0f..0f42e02436ee 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -1064,19 +1064,21 @@ pnfs_generic_pg_test(struct nfs_pageio_descriptor *pgio, struct nfs_page *prev,
                 gfp_flags = GFP_NOFS;
         }
 
-        if (pgio->pg_count == prev->wb_bytes) {
+        if (pgio->pg_lseg == NULL) {
+                if (pgio->pg_count != prev->wb_bytes)
+                        return true;
                 /* This is first coelesce call for a series of nfs_pages */
                 pgio->pg_lseg = pnfs_update_layout(pgio->pg_inode,
                                                    prev->wb_context,
-                                                   req_offset(req),
+                                                   req_offset(prev),
                                                    pgio->pg_count,
                                                    access_type,
                                                    gfp_flags);
-                return true;
+                if (pgio->pg_lseg == NULL)
+                        return true;
         }
 
-        if (pgio->pg_lseg &&
-            req_offset(req) > end_offset(pgio->pg_lseg->pls_range.offset,
+        if (req_offset(req) > end_offset(pgio->pg_lseg->pls_range.offset,
                                          pgio->pg_lseg->pls_range.length))
                 return false;