Commit 
a7d42ddb3099727f58366fa006f850a219cce6c8 ("nfs: add mirroring
support to pgio layer") moved pg_cleanup out of the path when there was
non-sequental I/O that needed to be flushed.  The result is that for
layouts that have more than one layout segment per file, the pg_lseg is not
cleared, so we can end up hitting the WARN_ON_ONCE(req_start >= seg_end) in
pnfs_generic_pg_test since the pg_lseg will be pointing to that
previously-flushed layout segment.
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Fixes: a7d42ddb3099 ("nfs: add mirroring support to pgio layer")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
                mirror = &desc->pg_mirrors[midx];
                if (!list_empty(&mirror->pg_list)) {
                        prev = nfs_list_entry(mirror->pg_list.prev);
-                       if (index != prev->wb_index + 1)
-                               nfs_pageio_complete_mirror(desc, midx);
+                       if (index != prev->wb_index + 1) {
+                               nfs_pageio_complete(desc);
+                               break;
+                       }
                }
        }
 }