NFSv4/pNFS: Fix a layoutget livelock loop

If NFS_LAYOUT_RETURN_REQUESTED is set, but there is no value set for
the layout plh_return_seq, we can end up in a livelock loop in which
every layout segment retrieved by a new call to layoutget is immediately
invalidated by pnfs_layout_need_return().
To get around this, we should just set plh_return_seq to the current
value of the layout stateid's seqid.

Fixes: d474f96104bd ("NFS: Don't return layout segments that are in use")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index ef14ea0b6ab8dc7b331792c73278d6439fa399ba..da5cacad6979e5df5d3afab1f0f02924660ee6c0 100644 (file)
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -347,11 +347,15 @@ pnfs_set_plh_return_info(struct pnfs_layout_hdr *lo, enum pnfs_iomode iomode,
                iomode = IOMODE_ANY;
        lo->plh_return_iomode = iomode;
        set_bit(NFS_LAYOUT_RETURN_REQUESTED, &lo->plh_flags);
-       if (seq != 0) {
-               WARN_ON_ONCE(lo->plh_return_seq != 0 && lo->plh_return_seq != seq);
+       /*
+        * We must set lo->plh_return_seq to avoid livelocks with
+        * pnfs_layout_need_return()
+        */
+       if (seq == 0)
+               seq = be32_to_cpu(lo->plh_stateid.seqid);
+       if (!lo->plh_return_seq || pnfs_seqid_is_newer(seq, lo->plh_return_seq))
                lo->plh_return_seq = seq;
-               pnfs_barrier_update(lo, seq);
-       }
+       pnfs_barrier_update(lo, seq);
 }
 
 static void