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From:   trondmy@kernel.org
To:     linux-nfs@vger.kernel.org
Subject: [PATCH 1/2] NFSv4/pNFS: Fix a layoutget livelock loop
Date:   Mon, 26 Jul 2021 07:59:19 -0400
Message-Id: <20210726115920.8518-1-trondmy@kernel.org>
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From: Trond Myklebust <trond.myklebust@hammerspace.com>

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>
---
 fs/nfs/pnfs.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index 4ed4586bc1a2..51049499e98f 100644
--- 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
-- 
2.31.1