net: forbid the reentrant RX

The memory API allows DMA into NIC's MMIO area. This means the NIC's
RX routine must be reentrant. Instead of auditing all the NIC, we can
simply detect the reentrancy and return early. The queue->delivering
is set and cleared by qemu_net_queue_deliver() for other queue helpers
to know whether the delivering in on going (NIC's receive is being
called). We can check it and return early in qemu_net_queue_flush() to
forbid reentrant RX.

Signed-off-by: Jason Wang <jasowang@redhat.com>

diff --git a/net/queue.c b/net/queue.c
index 0164727e39ad507857225d93a0886f5c24dfaad3..19e32c80fda730604fe7febf421f53cfdece567a 100644 (file)
--- a/net/queue.c
+++ b/net/queue.c
@@ -250,6 +250,9 @@ void qemu_net_queue_purge(NetQueue *queue, NetClientState *from)
 
 bool qemu_net_queue_flush(NetQueue *queue)
 {
+    if (queue->delivering)
+        return false;
+
     while (!QTAILQ_EMPTY(&queue->packets)) {
         NetPacket *packet;
         int ret;