From: Trond Myklebust <trond.myklebust@hammerspace.com>
Date: Mon, 26 Jul 2021 07:58:49 -0400
Subject: [PATCH] NFSv4/pNFS: Fix a layoutget livelock loop
Git-commit: e20772cbdf463c12088837e5a08bde1b876bfd25
Patch-mainline: v5.15-rc1
References: git-fixes

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>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfs/pnfs.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -317,10 +317,14 @@ pnfs_set_plh_return_info(struct pnfs_lay
 		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 || (s32)seq - (s32)lo->plh_return_seq > 0)
 		lo->plh_return_seq = seq;
-	}
 }
 
 static void