netdev-offload: Fix deadlock/recursive use of the netdev_hmap_rwlock rwlock.

When doing performance testing with OVS v3.1 we ran into a deadlock
situation with the netdev_hmap_rwlock read/write lock. After some
debugging, it was discovered that the netdev_hmap_rwlock read lock
was taken recursively. And well in the following sequence of events:

 netdev_ports_flow_get()
   It takes the read lock, while it walks all the ports
   in the port_to_netdev hmap and calls:
   - netdev_flow_get() which will call:
     - netdev_tc_flow_get() which will call:
       - netdev_ifindex_to_odp_port()
          This function also takes the same read lock to
          walk the ifindex_to_port hmap.

In OVS a read/write lock does not support recursive readers. For details
see the comments in ovs-thread.h. If you do this, it will lock up,
mainly due to OVS setting the PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
attribute to the lock.

The solution with this patch is to use two separate read/write
locks, with an order guarantee to avoid another potential deadlock.

Fixes: 9fe21a4fc12a ("netdev-offload: replace netdev_hmap_mutex to netdev_hmap_rwlock")
Reported-at: https://bugzilla.redhat.com/show_bug.cgi?id=2182541
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

0 files changed, 0 insertions, 0 deletions