tap: crash in multi-thread environment

In tap tx routine, virtio_interface_tx_inline, there used to be an
interface spinlock to ensure packets are processed in an orderly fashion
  clib_spinlock_lock_if_init (&vif->lockp);

When virtio code was introduced in 19.04, that line is changed to
  clib_spinlock_lock_if_init (&vring->lockp);
to accommodate multi-queues.

Unfortunately, althrough the spinlock exists in the vring, it was never
initialized for tap, only for virtio. As a result, many nasty things can
happen when running tap interface in multi-thread environment. Crash is
inevitable.

The fix is to initialize vring->lockp for tap and remove vif->lockp as it
is not used anymore.

Change-Id: I82b15d3e9b0fb6add9b9ac49bf602a538946634a
Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>
(cherry picked from commit c2c89782d34df0dc7197b18b042b4c2464a101ef)

2 files changed, 4 insertions, 1 deletions

diff --git a/src/vnet/devices/virtio/virtio.c b/src/vnet/devices/virtio/virtio.c
index 90acb75fa6d..a3fd05dbb55 100644
--- a/src/vnet/devices/virtio/virtio.c
+++ b/src/vnet/devices/virtio/virtio.c
@@ -83,9 +83,12 @@ virtio_vring_init (vlib_main_t * vm, virtio_if_t * vif, u16 idx, u16 sz)
 
   if (idx % 2)
     {
+      vlib_thread_main_t *thm = vlib_get_thread_main ();
       vec_validate_aligned (vif->txq_vrings, TX_QUEUE_ACCESS (idx),
 			    CLIB_CACHE_LINE_BYTES);
       vring = vec_elt_at_index (vif->txq_vrings, TX_QUEUE_ACCESS (idx));
+      if (thm->n_vlib_mains > 1)
+	clib_spinlock_init (&vring->lockp);
     }
   else
     {
@@ -230,6 +233,7 @@ virtio_vring_free_tx (vlib_main_t * vm, virtio_if_t * vif, u32 idx)
   if (vring->avail)
     clib_mem_free (vring->avail);
   vec_free (vring->buffers);
+  clib_spinlock_free (&vring->lockp);
   return 0;
 }
 
diff --git a/src/vnet/devices/virtio/virtio.h b/src/vnet/devices/virtio/virtio.h
index 57bb8d6c167..55b6271b337 100644
--- a/src/vnet/devices/virtio/virtio.h
+++ b/src/vnet/devices/virtio/virtio.h
@@ -135,7 +135,6 @@ typedef struct
 {
   CLIB_CACHE_LINE_ALIGN_MARK (cacheline0);
   u32 flags;
-  clib_spinlock_t lockp;
 
   u32 dev_instance;
   u32 hw_if_index;