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[net,4/4] net: dsa: sja1105: fix broken backpressure in .port_fdb_dump

Message ID 20210810111956.1609499-5-vladimir.oltean@nxp.com
State New
Headers show
Series Fix broken backpressure during FDB dump in DSA drivers | expand

Commit Message

Vladimir Oltean Aug. 10, 2021, 11:19 a.m. UTC 
rtnl_fdb_dump() has logic to split a dump of PF_BRIDGE neighbors into
multiple netlink skbs if the buffer provided by user space is too small
(one buffer will typically handle a few hundred FDB entries).

When the current buffer becomes full, nlmsg_put() in
dsa_slave_port_fdb_do_dump() returns -EMSGSIZE and DSA saves the index
of the last dumped FDB entry, returns to rtnl_fdb_dump() up to that
point, and then the dump resumes on the same port with a new skb, and
FDB entries up to the saved index are simply skipped.

Since dsa_slave_port_fdb_do_dump() is pointed to by the "cb" passed to
drivers, then drivers must check for the -EMSGSIZE error code returned
by it. Otherwise, when a netlink skb becomes full, DSA will no longer
save newly dumped FDB entries to it, but the driver will continue
dumping. So FDB entries will be missing from the dump.

Fix the broken backpressure by propagating the "cb" return code and
allow rtnl_fdb_dump() to restart the FDB dump with a new skb.

Fixes: 291d1e72b756 ("net: dsa: sja1105: Add support for FDB and MDB management")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/dsa/sja1105/sja1105_main.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
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Patch

diff --git a/drivers/net/dsa/sja1105/sja1105_main.c b/drivers/net/dsa/sja1105/sja1105_main.c
index 8667c9754330..b188a80eeec6 100644
--- a/drivers/net/dsa/sja1105/sja1105_main.c
+++ b/drivers/net/dsa/sja1105/sja1105_main.c
@@ -1635,7 +1635,9 @@  static int sja1105_fdb_dump(struct dsa_switch *ds, int port,
 		/* We need to hide the dsa_8021q VLANs from the user. */
 		if (priv->vlan_state == SJA1105_VLAN_UNAWARE)
 			l2_lookup.vlanid = 0;
-		cb(macaddr, l2_lookup.vlanid, l2_lookup.lockeds, data);
+		rc = cb(macaddr, l2_lookup.vlanid, l2_lookup.lockeds, data);
+		if (rc)
+			return rc;
 	}
 	return 0;
 }