NFSv4/pnfs: Fix the layout barrier update

If we have multiple outstanding layoutget requests, the current code to
update the layout barrier assumes that the outstanding layout stateids
are updated in order. That's not necessarily the case.

Instead of using the value of lo->plh_outstanding as a guesstimate for
the window of values we need to accept, just wait to update the window
until we're processing the last one. The intention here is just to
ensure that we don't process 2^31 seqid updates without also updating
the barrier.

Fixes: 1bcf34f ("pNFS/NFSv4: Update the layout barrier when we schedule a layoutreturn")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/pnfs.c

@@ -966,10 +966,8 @@ void
 pnfs_set_layout_stateid(struct pnfs_layout_hdr *lo, const nfs4_stateid *new,
 			const struct cred *cred, bool update_barrier)
 {
-	u32 oldseq, newseq, new_barrier = 0;
-
-	oldseq = be32_to_cpu(lo->plh_stateid.seqid);
-	newseq = be32_to_cpu(new->seqid);
+	u32 oldseq = be32_to_cpu(lo->plh_stateid.seqid);
+	u32 newseq = be32_to_cpu(new->seqid);
 
 	if (!pnfs_layout_is_valid(lo)) {
 		pnfs_set_layout_cred(lo, cred);
@@ -979,19 +977,21 @@ pnfs_set_layout_stateid(struct pnfs_layout_hdr *lo, const nfs4_stateid *new,
 		clear_bit(NFS_LAYOUT_INVALID_STID, &lo->plh_flags);
 		return;
 	}
-	if (pnfs_seqid_is_newer(newseq, oldseq)) {
+
+	if (pnfs_seqid_is_newer(newseq, oldseq))
 		nfs4_stateid_copy(&lo->plh_stateid, new);
-		/*
-		 * Because of wraparound, we want to keep the barrier
-		 * "close" to the current seqids.
-		 */
-		new_barrier = newseq - atomic_read(&lo->plh_outstanding);
-	}
-	if (update_barrier)
-		new_barrier = be32_to_cpu(new->seqid);
-	else if (new_barrier == 0)
+
+	if (update_barrier) {
+		pnfs_barrier_update(lo, newseq);
 		return;
-	pnfs_barrier_update(lo, new_barrier);
+	}
+	/*
+	 * Because of wraparound, we want to keep the barrier
+	 * "close" to the current seqids. We really only want to
+	 * get here from a layoutget call.
+	 */
+	if (atomic_read(&lo->plh_outstanding) == 1)
+		 pnfs_barrier_update(lo, be32_to_cpu(lo->plh_stateid.seqid));
 }
 
 static bool