[ovs-dev] [PATCH] dpif-netdev: Force port reconfiguration to change dynamic_txqs.

Ilya Maximets i.maximets at ovn.org
Tue Mar 24 23:50:45 UTC 2020

In case number of polling threads goes from exact number of Tx queues
in port to higher value while set_tx_multiq() not implemented or not
requesting reconfiguration, port will not be reconfigured and datapath
will continue using static Tx queue ids leading to crash.

 Assuming that port p0 supports up to 4 Tx queues and doesn't support
 set_tx_multiq() method.  For example, netdev-afxdp could be the case,
 because it could have multiple Tx queues, but doesn't have
 set_tx_multiq() implementation because number of Tx queues always
 equals to number of Rx queues.

 1. Configuring pmd-cpu-mask to have 3 pmd threads.

 2. Adding port p0 to OVS.
    At this point wanted_txqs = 4 (3 for pmd threads + 1 for non-pmd).
    Port reconfigured to have 4 Tx queues successfully.
    dynamic_txqs = (4 < 4) = false;

 3. Configuring pmd-cpu-mask to have 10 pmd threads.
    At this point wanted_txqs = 11 (10 for pmd threads + 1 for non-pmd).
    Since set_tx_multiq() is not implemented, netdev doesn't request
    reconfiguration and 'dynamic_txqs' remains in 'false' state.

 4. Since 'dynamic_txqs == false', dpif-netdev uses static Tx queue
    ids that are in range [0, 10] while device only supports 4 leading
    to unwanted behavior and crashes.

Fix that by marking for reconfiguration all the ports that will likely
change their 'dynamic_txqs' value.

It looks like the issue could be reproduced only with afxdp ports,
because all other non-dpdk ports ignores Tx queue ids and dpdk ports
requests for reconfiguration on set_tx_multiq().

Reported-by: William Tu <u9012063 at gmail.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2020-March/368364.html
Fixes: e32971b8ddb4 ("dpif-netdev: Centralized threads and queues handling code.")
Signed-off-by: Ilya Maximets <i.maximets at ovn.org>

Since the issue could be reproduced only with afxdp ports, this should
be backported only down to 2.12.

 lib/dpif-netdev.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index a798db45d..e456cc9be 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -4941,9 +4941,17 @@ reconfigure_datapath(struct dp_netdev *dp)
     /* Check for all the ports that need reconfiguration.  We cache this in
      * 'port->need_reconfigure', because netdev_is_reconf_required() can
-     * change at any time. */
+     * change at any time.
+     * Also mark for reconfiguration all ports which will likely change their
+     * 'dynamic_txqs' parameter.  It's required to stop using them before
+     * changing this setting and it's simpler to mark ports here and allow
+     * 'pmd_remove_stale_ports' to remove them from threads.  There will be
+     * no actual reconfiguration in 'port_reconfigure' because it's
+     * unnecessary.  */
     HMAP_FOR_EACH (port, node, &dp->ports) {
-        if (netdev_is_reconf_required(port->netdev)) {
+        if (netdev_is_reconf_required(port->netdev)
+            || (port->dynamic_txqs
+                != (netdev_n_txq(port->netdev) < wanted_txqs))) {
             port->need_reconfigure = true;

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