2021-07-26 12:00:36

by trondmy

[permalink] [raw]
Subject: [PATCH 1/2] NFSv4/pNFS: Fix a layoutget livelock loop

From: Trond Myklebust <[email protected]>

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 <[email protected]>
---
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